The AM Forum

Fabio's final tube exit temperature was about 84 degrees the other day. I figured it's time to build a rig for the summertime.

Here's my new flame named "Rico Suave." (Ree-co - Swa' vay)   Rico will be a 24 pill PDM class E rig.  I work on it a little each day. It all adds up. The RF tank circuit is now installed using vacuum variables and turns counters. He will have a sequencer, all full digital drive - even a digital VFO with frequency readout.

Rico will be self contained with everything in a 24" tall, 19" wide cabinet.   Of course, the guts will be viewable thru Plexiglas.

The heatsink in the front will house the PDM modulator MOSFETS. The rear heatsink is for the (24) 11N90 MOSFET RF finals.

I plan to have Rico Suave band switchable for quick 160M and 75M capability.

Pictures will be posted as he gets built and tested.  Most of the parts are on order.   See the PDM generator pictured below and the beginning of the PDM filter.  The vacuum variable caps are mounted on fiberglass sheet cuz the main tuning cap (C1) must float above ground. The coupling shaft for C1 is well insulated.  

The 4" hole in the front Plexiglas is so I can stick my hand in there to feel how hot the pills are running - and make occasional measurements, etc.

Notice the burn marks on the front heatsink. Those are the remains of my last 20 pill class E rig I built about 6 years ago... I jacked the HV up too high and paid the price. It did run FB for 9 months however....  ;D

Wish me luck!

T

Excellent Tom!  You may consider 40 meters for spring and summer as I hope to stir up some activity on 40 and 20 meters. 

John

Neat stuff Tom.

But I wonder what all those big electrolytics are for?

To pad the rig for occasional 18 khz operation?   ;D   (The 5KVA power transformer is also located in the back, below the electrolytic caps)



BTW, Bruce, I understand you built one of the digital VFO's and the big blue readout ?   Is there standard documentation enuff to built one somewhere?   I could dig thru the E site, but thought you might have it posted handy somewhere...

Wow. It just looks so....so.....vacant compared to a Fabio or Dr Love. You know, you could've just gotten a Flex radio and joined in the SMUG....  ;D

Some comments you could hear:

"Nice cabinet, when's he gonna put a radio in it?"

"Did he paint it with invisible paint?"

"He needs to feed that thing some red meat"

"Plexi-King, my ass"

"Oh yeah - this is that kid who ran a Gotham vertical hyper-tuned with 3 feet of coax, it all makes sense now..."


All kidding aside, I'm sure you'll have fun with it, Tommy.  You always do. ;)

"I got a 24 pill! a 24 pill! And a muddy watta slappa! !"   ;D  ;D


or, will it be Tom and Rico's most excellent adventure..................

Tom,
That inductor is way to big unless you plan to work 600M.

Hi Tom,

Looks like a good start!  You probably won't need too much of that inductor....  and it is more efficient to use 2 inductors than one.  Don't short out any turns under any circumstances.  With my rig, I use 2 inductors at 90 degree angles to one another, and short out the 160 meter coil when on 80 meters.  Anytime there are shorted turns, you get unnecessary heat and power loss.  You could leave the end "hanging out" for 75, but individual coils is much better.  You could also put the inductors one above the other and that would work as well.

Suggestions:  Don't provide any ground paths from the power supply to anything other than the modulator heat sink.  Create a single, contiguous ground plane with the modulator heat sink and the filter ground (extend the heat sink if necessary with a piece of stiff aluminum), and build the filter over this with all PWM filter capacitors tied into this ground plane.  Doing this will minimize "coupling around" the filter through the ground.

Are you interested in an experiment?  You could use magnetics rather than air would inductors for the last 2 inductors in the PWM filter.  Now, if you did that, you would need to break the filter into 2 paths following the first input inductor.  Yes, it would most likely be possible to construct a single filter using magnetics, but the current is quite high under heavy positive peak modulation, and the filter must be designed around this, and not the carrier (unmodulated) DC current.. Stacking cores does not double the current, and I fear you be stacking many of them to create a single-path filter.

So, you would have an air wound input inductor of some (relatively small - maybe 12uH) inductance as the input inductor, and then break out into 2 paths.  Each filter would serve 2 modules.  You would significantly reduce the size of the filter.  Magnetics has a new material called X flux, which is just about as good as Hi Flux, but is quite a bit less expensive.  I have 24 of them here for my next transmitter, which will use an air core inductor as the input and magnetics for everything else.  The filter will be very small as compared to using air for everything.  Just an option I though I'd mention...

Tom, with that big rig I'd tend towards an analog L/C VFO instead of a DDS...  I built one of the N3ZI DDS kits and I'm not too thrilled with the phase noise performance.  I don't have anything here to accurately measure phase noise, but I hooked it to my Agilent service monitor and it's sayin there's a 500 Hz or so FM deviation on the signal.  Compare that with a 6BQ7 Franklin VFO I whipped together for a HB RX project, the Agilent sez 50 hz FM deviation.   Course the voltage out on the 6BQ7 VFO is a lot more, but I can certainly hear the noise difference when listening to both in a RX.

Otherwise the N3ZI kit is quite nice and simple.

Here is a picture of my pulse width modulator that modulates the same transmitter you're building.  This one uses air core inductors.  The PWM output section is visible mounted on the heat sink, and the overload shutdown board can be seen to the right, above the large knife switch.  The overload board is not mounted to anything other than the heavy wires going in and out, which are more than sufficient to hold the board in place.

The heat sink surface was extended with a piece of aluminum, and the filter constructed over the resulting ground plane.

(http://www.classeradio.com/rig_back_1.jpg)

Will this turn into a TV series with the love life of Fabio and Dr Love and who is the new kid on the block?

Phred

OK, Johnny, on the digital phase noise. I wonder if Bruce or Steve have measured the noise on these VFOs?  I haven't studied it all yet, but intend to soon.  If need be, I could easily go with an analog watt or so from my ricebox as RF drive for the new digital drive board, if need be.

Steve, I will probably stick with the air PDM coils simply cuz that's what I am most familiar with from the last PDM E rig. I do like your idea of mounting the complete filter on the heatsink/ groundplane of the PDM modulator.

Yes, the tank coil is too big. I figured I wud tap it (not short it) for both 160M and 75M and see where it worked out. I can easily cut the coil and shorten it later.  I have bigger 3/8" coil stock too, but thought it wasn't enuff for 160M.  I still need to know what the approximate inductance will be on 160M and 75M??

Frank, the new PDM driver board requires a 12V pulse out of the PDM gen. My old Rev C board puts out 5V. Maybe you have a simple chip/circuit I can add to amplify it to 12V?  I don't want to have to build a new PDM gen just for that minor issue.


It's good we post our thoughts and solutions here to make this an ongoing construction project. Putting it all together is not easy the first time through and this will help others who are on the fence.  This project is somewhat overwhelming when looked at overall, but when taken in small chunks it can be digested.  


Just axe Rico Suave.  (Ree-co    Swa'- vay)

T

Tom, An IXDD414 would make a great level shifter and easily drive a long cable. Plenty of drive so you could terminate the far end at 50 ohms so there is no ring.
Short run you could use a smaller clock driver 4427 I think is noninverting.
You will be a lot cleaner with a solid ground system under the whole modulator.
This way you don't have high frequency currents floating around the cabinet.

Nope, not me...
I use Steve's hartley, and NO readout..
I don't need one, as I use an SDR reciever...
Just hit the spot button, and tune by sight.

 ;D

The N3ZI DDS is nearly useless....

Noisy as h*ll, and you still need a follower amp to get usefull levels..

My O-pinion.

The NORCAL kit was much better...
But until they get off their year long vacation... those kits are unobtainium.

OK on using the IXDD414 Frank for the PDM gen leveler.  I'll order one and install it.

Guess I'll stay with an analog VFO then, Bruce. I guess it was Wayne/SSJ who just built one as well as Steve.



I was just looking to pimp my new digital ride a little:

No they didn't Tom....

They bought "sold for CB" type frequency counters, with the big blue displays.
To go with the Hartley oscillators they built.

Hey Tommy, I've been messing recently with Franklin VFOs.  By far superior to any Hartley or Colpiss I've ever built.

It has two advantages - you can bandswitch easily since the tank only has two terminals - one goes right to ground with no funky taps  (L or C) for feedback.  Also it's very stable due to the very light coupling from the tank to the active elements.

The 6BQ7 VFO I previously mentioned achieved <50 hz/hour drift with no temp compensation tricks.  You can build one just as easily using JFETs.  Use one of those cast aluminum boxes for rigidity...

BTW did you ever get that package I sent ya a while back?

Bruce, OK, I see.  So they went analog for the VFO itself. When Steve mentioned, "all digital drive" I assumed he meant the VFO too.  I'll stay with the ricebox "VFO" drive then since I use it for everything else.

Johnny -  Yes, I got the package, but sorry, can't remember what it was. Was it a CD? I've had trouble wid my CD player and couldn't play it if it was...  Tom Vu get thousand of package a day from well-wisher, so you understand... ;D

T

Hi Tom,

The oscillator itself is a hartley and everything else is digital.  I find it far preferable to using a rice box for a variety of reasons, not the least of which is simply ease of switching and much lower heat generation.  Rice boxes (at least all the ones I've seen) get quite warm, even in receive.  And, you tie up a whole multi-function piece of equipment just for VFO service..... and there's the human error factor (power up too high, not selected, etc. etc. etc.).

On the PWM generator, you could use an IXDD414 and it would work quite well.  Here is the output circuit from REV D of the PWM generator.  The output of the PWM generator chip is fed (in 12V mode) directly to a complementary pair of transistors (a 2n3904/3906 pair).  I have about 8 feet of 50 ohm coax between my PWM generator and the PWM output.

(http://www.classeradio.com/pwm_generator_output.jpg)

Hey, Tom - I would like to come to your shack the day you are ready to fire everything up  :D  Can also go over a whole lot of things.  Always fun to see a new rig being "born"  8)

Then sushi afterwards !

Was 4-pack of DVD roms Tom

here's the official music video to Tom's rig:

http://www.youtube.com/watch?v=xeX9zoWSut8

I should do a mixdown of this , bet I get plenty of LOL's.  8)


then a ambulance ride! get down!  :P

I eat it raw, like sushi.   ;D

NOT good to read this, John. I built the N3ZI DDS to be a VFO for a Class D TX. Would this shift be heard over the air? Or wuld this be unacceptable as a L.O. in a RX?
Also reading feedback from others here who have built the N3ZI. Noisey and not enough ooomph???  Norcal still hard to get?

Good vid Tim
FRED

HAHAHAHA!!  Gawd that video was funny enuff to bring tears to my eyes, Derb.  I haven't heard that in years.  Yep, that's the official Rico Suave Class E song. Just like when they play a song when the WWF or MMA fighters come out.    

I can see it being played in the background when Rico gets fired up for the first time on the air... ;D

T

Are these digital panel meters OK for using with RF?  At only $9 each, they're cheaper than analog meters and pretty cool looking for monitoring the four module's current and voltage.

Is anyone using them now or at work?


0-100A Blue 3.5" Digital meter:

http://cgi.ebay.com/3-5-Inch-Blue-LED-Digital-AMP-Panel-Meter-DC-100A-Shunt_W0QQitemZ370301414274QQcategoryZ25411QQcmdZViewItemQQ_trksidZp4340.m8QQ_trkparmsZalgo%3DMW%26its%3DC%26itu%3DUCC%26otn%3D20%26ps%3D63%26clkid%3D8360502073947355137

0-199V Digital Meter:

http://cgi.ebay.com/NEW-3-Digital-Blue-LCD-DC-0-199-9V-Volt-Panel-Meter_W0QQitemZ270490090047QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3efa773a3f
T

I thought about those too...

However.....

My handheld digital VOM  will NOT read correctly trying to measure the DC from the PWM modulator....

Maybe I needed more bypassing or some such...

But it has always been said to use an analog meter... so I've stuck with them

I pay $8 each for my panel meters....

I don't care what brand they are....

I'm not going to pay more than $20 each for a panel meter for any reason.. !

Heck I'm not building a nuke reactor here!


If you decide to try those Tom, please let me know how they work!

That would make an E-Rig look super spiffy!   ;D

Fred, prolly up to a hundred or two watts the N3ZI kit oughta be OK and won't cause too much neighborly trouble.

It needs a better frequency reference.

I would use analog meters.  You can see a whole lot more  ;)

Here's a schematic.  A lot of people have asked for it.

http://www.classeradio.com/class_e_24_fet.pdf (http://www.classeradio.com/class_e_24_fet.pdf)

For Printing:

http://www.classeradio.com/class_e_24_fet_top_half.pdf (http://www.classeradio.com/class_e_24_fet_top_half.pdf)

http://www.classeradio.com/class_e_24_fet_bottom_half.pdf (http://www.classeradio.com/class_e_24_fet_bottom_half.pdf)

I tried posting a .jpg of the schematic, but it was not readable - too many components to shrink to 8 inches wide!

Steve,

The schematic makes everything clear, thanks!

Questions:

What are the voltage ratings for C-shunt (.15u) and C-Bypass (1500pf) ?

Could the FOUR 12V regulators for the digital drivers be substituted by using ONE 10A 12V regulated supply?

I see that the input tranzorbs have been eliminated. Are they used on the input of the phase splitter board if used with a ricebox?

BTW, reading the "official" site archives back in 2008, Frank/GFZ came up with a nice PC board to hold the digital driver chip and RF MOSFET leads and associated parts. Has anyone fabricated this board? Any idea how to knock one out easily?  This board  wud complete the board set and get rid of the clap-trap mess on the RF heatsink.  I attached it below.


BTW, the link above on AMfone for class E had me wondering where all the "meat" was.  The REAL good construction info and threads are located at the "Official" Class E Website:  

http://www.classeradio.com/

We should probably have a link to get there to avoid confusion to others, as it did me. I spent a day reading the "official" site and will continue to until I digest the latest dope. For newcomers, this is probably the best way to get up to speed. Then pick out a schematic or rig config and start writing down what is needed to pull it off.


T

GFZ  universal digital driver/final board:

Hi Tom,

The shunt capacitors (1500pF) are very specific parts, so the voltage rating (500 volts) is part of the specification.  No other parts should be used other than the ATC100C series 1500pF caps.

The bypass caps - I use 150 volt or better.  The current rating is the key.  I use 2 or preferably 3 orange drops in parallel.

Right on the transzorbs - but there IS  a transzorb across each group of drivers to protect them in the unlikely event of a failure getting back into the drivers.  You don't want an avalanche (sp?) condition.

Regards,

Steve

The TransZorbs are across the driver power supplies to prevent, in the unlikely event of a failure, any high voltage getting back into the driver power supply and cascading through the system.

On the power supply question, you could use a single supply for all of the drivers.  Those simple switching regulators are very nice; small and efficient which is why I use them.  Usually, big supplies are either poorly regulated, or are analog (linear), and waste a lot of power in the form of heat.  I have seen some good switchers out there - maybe that's what is proposed here  ;)

Regards,

Steve

OK on all Steve.  Then I'll use a single 12V switching supply for the DD Vcc.


Today I stopped down at the local scrap yard and found a few sheets of brass at $2 /pound. These make great capacitor bank connections as well as RF MOSFET connections.

It's a small step, but here's the BEER CAN main cap bank ready for action. A little here, a little there. After a while it adds up to big db... ;)

This is 35,000 ufd at 150V for Rico Suave.  


Hmmm.....  Now that I look at it, should a bar be soldered across at the center - shorting the the five center stubs together  - or is it correct as-is?

T

How about using  computer power supply for a driver source?

I like this project, hope to follow it to completion here.

Good idea.  Though I picked up a switched 12V, 20 amp supply for $38 on e-Bay tonight.  It will power the digital driver as well as some other low power 12V points on the other boards.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270487051020&ssPageName=ADME:L:OU:US:1123

I've been ordering parts and digging out what I'll need. There sure is a lot to building this rig.

I've been looking into making the digital driver and RF final area as compact, RF-friendly and stable as possible. I think eliminating those driver transformers and wires is a good step. They will be replaced with a QIX phase splitter board and the digital drive 1XX414 drivers on the heatsink.  Short leads and fat conductors.  

I'm cornvinced 24 pills using robust devices like the 11N90 will put out more power than we are accustomed to when the layout is tighter.  This includes the output transformer layout and lead length. We'll have to see.  Thanks for your layout advice and new ideas, Frank.

T

There is a whole new world to observe out there when you can see 1GHz on your scope. Open up your rice box and look at the final amplifier strip. There is a good reason for a clean layout.

I wanted to keep this project updated as it progressed. The new 24 pill PDM rig is now about 60% finished. The sequencer, shutdown board, PDM generator, PDM power board, 135V power supply and control wiring are all set. The RF modules and interconnecting wiring need to be wired.

Notice there are two PDM power boards and room for a second shutdown board. The reason is that I may add another 24 pill RF set of modules to make it a 48 piller in the future. Depends on how stiff the on-air competition continues to be.... ;)

Notice the RF unit has 10A meters mounted (viewed thru the panel Plexiglas) and is fully digital driven. There is a small A/D board mounted that will permit direct drive from the ricebox RF driver with 1 watt.  The ferrite core transformers are mounted and held down with plexiglas.

I hope to have something working in a few weeks or so.

73,

T


1)  24 pill RF deck with digital drive, output transformers and 10A old buzzard meters.

2) Two PDM power modulator boards

3) Sequencer and Overload board ready to be mounted in top modulator cabinet

1) Top view of power supply wiring. There is a sheet of plexiglas mounted above the filter caps that supports the relays and associated components.

2) Lower cabinet ready for RF deck tenants

3) RF deck. Full digital drive.  Huge heatsink.

N3ZI has a new improved DDS VFO. http://www.pongrance.com/super-dds.html (http://www.pongrance.com/super-dds.html)
More expensive but much better specs than the old one.

If you want one.....

I'll send you one for the shipping cost....
Built, but needs improvements   :)

I'll never use it ....

Thanks for the generous offer, Bruce.  (and the VFO info, Terry)

Do these VFOs generate phase noise that may be heard down the band with a big QRO signal? What is the disadvantage of using one?

I understand it is important to run them at X2 freq to keep the VFO signal from interfering when in receive mode.

The reason I went with the A/D converter is to be able to keep transceive capability, which I like. Separates can be a pain to zero beat, etc.  But I'm always looking for new dope to change my ideas.

T

Yeah they generate a ton of crud...
AND only generate 200mV +/- pk-pk output.

so would need filtering and amplification to drive, well, anything really...
At the very least.

They are a very simple kit, not a lot of parts, so they are good for just general use aound the shack, when you need a quick signal for testing, but I would not recomend them for a QRO rig.

bruce

Running the VFO at 2X  (or more) does give the advantage of not interfering with RX.
And any drift, or what have you is also divided by half, making it at least appear more stable on freq.

Makes getting 2 square-waves out of phase a tad bit easier too...
Not much, but a little  :D

I think the older N3ZI DDS has too much phase noise for a big rig Tom.  Not sure about the new one.

It seems to me that most of the troubles guys have with Class E rigs center around them using riceboxes for drivers.  They have problems with key up spikes, forget to turn the power down, or whatever, and BAM a bunch of fried FETS.  Steve's design is robust enough that barring drive issues there's not much that can fry a FET otherwise.

My suggestion:  bit the bullet and build a 7 MHz VFO.  Use the Franklin design - it's more stable than anything else I've built - 10 hz/hour drift using a tube.  Cut a hank of good stiff B&W coil stock, find a good quality variable cap, and firgure a series polystyrene cap to get the tuning/resonant range you want.  I think you have some of those National dial drives from your telescope projects - this would be an oustanding place to use one.  Hang a 7474 divide-by-2 off the output and yer done.

Tom,
Since you have an HP606 I suggest you check the reactance of an orange drop cap at RF. Put it in series with a 10 ohm resistor. You are trying to bypass a 5 ohm source so you need lower than 1/2 ohm reactance. I would put some ceramic caps in parallel with the OD cap. Those RF chip caps work well at RF much more stable than dork knobs. If you want to save some money get the ones without foil and lay them between the source and drain leads.

John,

That sounds like a great idea.   I could use the A/D converter already in there to take  1 watt and convert it to digital drive. Do you have a working schematic of a suggested Franklin?  I wonder if it will need a buffer before the A/D?

Will the A/D converter generate its own phase noise or is this not an issue?

What is the reason for using a tube vs: a signal transistor or FET?   



Frank:  What's an OD cap?  What orange drop bypass caps do you mean, the bypass caps at RF deck's modulation input (.15's?)    Or the 1500 pf ATC caps at the RF drains?     I already have quality ATC caps coming for the drain bypass.  I only have 0.15 orange drops for the input modulation bypasses, however.

T

the OD is orange drop and they are not a good bypass at RF. Check them you will see. The only high value film cap that was worth a darn was made by Sanders Associates. I put a bunch of .005uf discs in parallel with the OD to get a HF good bypass
Do a reactance sweep with your HP606 you will see. I bet you see the reactance take off above about 800KHz.
Build a VFO with a FET with a second one as a source follower

OK, OD is orange drop.... duh...

So you're saying the 0.15 cap at the bottom of each RF output transformer  (where the PDM power comes in)  needs to have additional bypass caps for the higher RF freqs.  How about a 1000pf doorknob there in addition to the 0.15 orange drop?   I'd hate to spring for expensive ATC caps there - I need 8 of them for the full job.

T

You can use FETs for the Franklin oscillator, Tom.  The big advantages are (a) very light coupling to the tank so the drift is focused there, not in the active devices and (b) one terminal tank (one end grounded) making bandswitching really easy.

I think your "A/D converter" isn't really an "A/D converter" but rather a Schmitt trigger that just squares off the sine wave.  A real A/D converter will convert a voltage into a binary number representation.  No reason I can see for that in a class E xmitter.

Anyway, if you use a good Schmitt trigger (74AHS series is one) you won't notice the phase noise, particularly since you're dividing by two.

Skizmatic:  http://homepage.eircom.net/%257Eei9gq/lo.GIF

Thanks for the schematic, Johnny.

I printed it out and it's on my list of thangs to do for now.

The "A/D" converter is a phase splitter to drive the two p-p RF modules.  I don't know how the sine to square wave conversion gets done until I get a schematic from Steve/ QIX.

As alternatives, I have an old tube Collins PTO I may convert over to an FET.  Or, if anyone knows of a analog VFO kit out there, let me know.

T

Here's what the RF deck looks like all wired up.  Pictured are (24) 11N90 RF Mosfets driven by (eight) smaller  IXDD414 drivers.    Full digital drive.  I need to build up a VFO yet.

The rig is maybe 65% finished.

T

  

Tom,

Here's Steve's  VFO circuit...

It is Hartley vfo, into 74ac112 Flip-Flop that squares off the sine wave, into 2 phases 180 deg .

Then there is adjustment for duty cycle of those square waves...

Just what you need....

Or, you can get Steve to send you the newer schematic....

But I still use this one in my own rig, and works fine...

http://classeradio.com/vfo_2_band.pdf

I can see some room for improvement with the oscillator.... I wouldn't tap directly off the tank to the buffer amp with that 8K resistor, nor would I use a twisty gimmick for the coupling - that's begging for some mechanical instability.  The strategy of using min coupling to the tank is sound, but a 10 pF or so trimmer solidly mounted would be a definite improvement, as would coupling from the emitter of the oscillator transistor to the buffer.

THe most important thing is using good components in the tank, though.  Air-dux or B&W stock (as heavy a wire as you have) is great.  A high C/L ratio works best for stability.  Minimize the trimmer capacity as much as you can, they're another source of drift.  Use good quality fixed polystyrenes instead and connect the tuning cap to various coil taps until you get the tuning range you need.  A 10 pF N750 disc cap in parallel with the tuning cap will help knock out any residual drift.   I didn't need any temp compensation in the Franklin I built using a 6BQ7 - and I got a good 20 volts of RF outta the thing at 100V B+.

Johhny and Bruce -

Ya know, I actually have an old Collins tube PTO that I replaced with an FET.   I modified it to tune 3.5 - 5.5, but cud change it to 7mhz easily.  I shud use that little battle ship as the core and add a buffer stage to that.

I checked it out the other day and worked FB.

T

Tom,

   That VFO since it runs 7-8 Mhz continuously is a natural for a "Huff & Puff" VFO stabilizer. There are many H&P discreet circuits, but to me one stands out, and that is the X-Lock 2.0 from Cumbria designs.
This is a PIC based H&P which will lock your VFO to a +/- 10 Hz window. The cost is about 20 Euros.
It samples the frequency and then creates an error voltage to correct the frequency with an AFC like control circuit. The kit uses an LED as a varicap to use with solid state oscillators.

      I use one on a tube VFO which works very well for me. With a tube VFO it will be necessary to have good regulation of the B+ and filament voltage. I use dual 1N4005 diodes as 'varicaps' which work very well without VFO rectification.

      The links below take you to the Cumbria Design web site, and to what I did to make this X-Lock work with a Lakeshore "Band Hopper" 5-5.6 Mhz VFO.


       Once you try X-Lock, you won't go back. This H&P is that good.


http://www.cumbriadesigns.co.uk/x-lock.htm

http://pages.prodigy.net/jcandela/Band%20Hopper/

Jim
WD5JKO

Be careful with these huff-n-puff circuits though.  You can't use 'em to polish a turd.

If the VFO drifts to the point where it's outside the ability of the loop to maintain lock, it's gonna go spinning into orbit and probably suddenly jump a couple KHz or more.  With a RX you can tell when this happens.  Not so with a transmitter till you turn it back after your old buzzard and everyone's laughing at you.

I find it easier just to do it right in the first place... but if you get the VFO drift within reason one of these circuits will make it rock stable.

I have a receiver with this feature (a Sylvania R-1414, as well as a HP 8640B with the same arrangement) that use the 100 hz digit off the freq counter to maintain lock.  I wasn't at all impressed - you hafta unlock it before you tune and if it's locked on the edge of its tuning range, it'll lose lock with the attendant frequency jump.

That's a fact  ;)  But, by the same token, the oscillator works very well and is amazingly stable as long as you're not bouncing it over a bumpy road  ;D   The thing that might be helpful would be temperature compensation.

I went for K.I.S.S. ; reliable and simple.  But, there are better basic oscillator circuits out there....If you want to do the extra work!  8)

Regards,

Steve

I haven't tried that Franklin with the FETs I posted, but the one I made with a 6BQ7 was by far the most stable VFO I've ever made.  No temp compensation either.  About 100 hz drift from turn on, and about 5 min later 10 hz/hour drift.  You can knock the thing on the table and it'll shift about 100-200 hz - mostly because of the bigassed airwound coil.

Mebbe I'll mess with it this weekend and build one up.  I'm not a big fan of the Colpiss anymore...

That RF stage is slick. Gonna make all the keyclowns cry.

Fine work Mr. VU!!!!

I've decided to add a VFO to the rig.  Instead of driving Rico Suave with a ricebox, the VFO will be used with a divide by 2 digital circuit and a phase splitter to drive the class E RF finals.  A ricebox is prone to key up spikes and full power mistakes that can blow out the RF fets in a microsecond.  The low level VFO circuitry as shown below is more controlled and stable as a driver.

It was not an easy task to get the unit mechanically stable. The first variable capacitor I used had a mechanical resonance and had to be replaced.  There is also a fine tuning capacitor.  I plan to add a frequency counter to the output.

Tests show the unit to be very stable and drift is less than 10hz over a 10 minute period. I can also push and pull on the cabinet and the frequency barely moves around.   With the divide by 2 for 75M and divide by 4 for 160M, it will be even more stable in all aspects.

I still need to add the digital divide / phase splitter board into the next compartment. The VFO is fully shielded from the digital board and outside whirl.

This should be a nice addition to the new rig and make it completely homebrew from VFO to antenna.


I've posted the schematic for those interested.

T


Picture #3:  

Top - VFO  
Middle - PDM Modulator    
Bottom RF Deck

VFO and splitter/ digital driver schematic-

http://www.classeradio.com/vfo_2_band.pdf

I find the huff n puff in the HP8640B a problem that adds to phase noise. Much better to let the generator warm up for a 1/2 hour so it is stable.

Tom,

That is NOT the schematic of the board you're using.

bruce

only huffin an puffin going on will be when that things keyed down on the channel.

how about a built in SBE warbler - push a button and the vfo strobes about within about a KC range - would drive slopbuckets kray zee   :D  but nobody on am would notice unless they have a sync detector, then you'd drive them kray zee too.  :(

Hmmm.....  let me check into that, Bruce. Thanks.

T

Yup - my sync AM does NOT work on Timtron's SBE -- gotta go regular AM and go wide.  Then it ain't half bad

Al

Bruce,

Yes, the present splitter board I have is set up for a ricebox.

But it can be configured for a VFO as shown in the schematic.

The board doesn't include a VFO which I already hand wired and is working FB.

T

Tom,

Yup, just wanted you to be aware that the board I sent you does not go with that schematic...

Though the VFO section (only) of that schematic CAN be used with the board....

We all built that circuit up completely dead-bug, or perfboard style.

Works ok-fine, hi-hi, fb, om...    ::)

We're progressing slowly but surely.

Here's the red PDM filter for your viewing pleasure.

The inductors are 28.8 uh, 28.8 uh and 14.1 uh.   I measured them using a signal generator and scope - put a cap across the coil and found the parallel resonance point. Very accurate.  Thanks to Jay, W1VD, for modeling the values for this "infinite impedance" PDM filter for me. In simulation it appears to have excellent ripple characteristics.

Notice the positioning of the coils so that they are all at rights angles to one another. This will keep coupling small and the filter will have good isolation.  I could always add shielding if needed later.  The coils each use #6 wire for good Q. The aluminum ground plane below is important as well as the distance each coil is from any objects. (At least one coil diameter.)

The coils are wound on 4.5" PVC pipe and have a good length to diameter ratio giving optimum Q.

I will need to build a second PDM filter, a duplicate of this one, if I plan to add on and make this a 48 piller later... ;)

T  

I wish I was not as indoctrinated and set in my ways as Mr. Vu. When he builds he just rolls it and straps.

I kept my racks and my big plate iron, let em cool off for a year or two and maybe I'll hire a machine shop to cut my stuff and start up again. On ice for now. I need to operate and have fun on the air for a while.  :D

Yep, "operate and have fun on the air for a while."  I'm not sure I've been keeping to that 2010 resolution lately, Derb... ;)

Lots of this building is right on my edge of abilities and understanding. So, I learn a lot and get stretched all the time. I'm always sending out emails looking for advice from the gurus here...

So, likewise, you're doing what you can there and the big iron you have coming soon will be a great filler for operating while you decide what to do with your homebrew stash of parts. A mix of both is good. Once you get a big mawl on that sounds really good (Raytheon) the pressure will be off and you can slowly put together what you want at a leisurely pace.

I know the Derb BJB will be back in FB form to strap the summer static - soon.

T

Nice filter layout Tom. (Nice to see layouts that don't look like they fell off the back of a cow.)
Keep an eye on temperature rise with the caps you might need more lower values in parallel.

Thanks, Frank.

Well, actually, you're seeing the results of your advice over the years.  That last 4X1 PDM filter system I built is laid out like this one. I'm simply using your information on layout and general practices.... ;)

Those orange caps should be OK. They are the same ones I used with the last 20 pill MOSFET rig I built six years ago, just different configs. They didn't get warm back then.

You will notice in the third filter picture I have the diode (and filter cap) that dumps spikes into the power supply  - it's mounted near the output, ready for action.  I might even mount a trap there to further attenuate the residual 140kc switching frequencies. I still have the old series trap lying around. We'll see if it's needed first.

T
 

I added the last transorbs, RF bypass caps, input RF drive connections and assorted stuff. The 24 pill RF deck is officially ready to fire up and test. However, I will hold off until the rest of the safety infrastructure is wired up and the rig is a complete package.  Then we just gots to flip the switch and play the Rico Suave tune... ;D

Looking at all the work required for just 24 pills, I'm not sure I wanna do this again to make it 48... :o

I hope this series of posts is giving others the encouragement needed to do their own class E rig project!

T

Tom,
The diode on the output of the filter. Put a cap to ground right at the cathode. Reason. The wire back to the power supply will have some inductance. This will limit transient current. A cap will provide a nice place to dump any HF transient.
Come up slow and measure every gate. I'd measure every gate before I put any drain voltage on the final. Then feed it a few volts and see how the gate waveform changes. It is all about that wiggle as the gate goes through 5 volts or so. Also keep an eye on the driver  voltage and make sure there is no high frequency crap on the 12 volt rail. Good luck

Yep, there's already a 0.5 at 2KV cap on the diode's cathode to gnd. Did you mean to make the lead shorter? It's about 2" long now.  Refer to the 3rd picture of the PDM filter.

OK on the fire-up precautions. It will be a week or two yet cuz I wanna wire everything up first and have protection, etc. Still have a ways to go before I start the final assembly.   

T

2 inches is better than 2 feet. Also the Damper diodes need a local bypass an OD in parallel with one of those  680uf/500 volters would be nice if it will fit (if there is any distance back to the supply).

Damper diodes?  You don't mean the diodes on the output of the PDM modulator?

Or do you mean the single diode that dumps the residual PDM filter spikes into the power supply as mentioned before?  I have 0.5 uf to gnd at the diode cathode. Are you saying to put a big 580 uf cap there too?  It does makes sense since the PS is about 3' away in cable length.

T

Tom,
I'm a dope, diodes go to ground in a floating modulator. But it would be a good idea to have a cap at the drains of the modulator FETs. A 680uf would be a nice low Z source. Otherwise you have the inductance of the wire back to the supply limiting current during short pulses. I think there is a cap on the output board but not that big.

Yep, there are a pair of 560 uf caps - one at each end of the modulator FET drain bus already.  Steve had that covered.


Well, now all I have left is to build the phase splitter / driver board and then start integrating the whole system together. That in itself is a big project considering the many supplies, shutdown board, interconnections, digital meters hook up, etc.

Got my blue-digit freq counter for the VFO yesterday, so got all the parts to finish the job.

T

One of the guys building a class E rig wanted to know the capacitor values of the PDM filter.  Bear in mind this filter is designed for 24 pills and has an output load designed for 1.75 ohms.  If using a different load impedance (more or less MOSFETS) then the filter values will change.




(I cannot post the SwitcherCad schematic cuz it's in .asc format, not allowed here)


Six Element Butterworth infinite impedance low pass filter:

The values are:  L1= 28.8 uh    L2= 28.8 uh    L3= 14.1 uh

C1=10.7uf    C2=7.3 uf    C3 = 1.6 uh.

Remember that the C3 value is in parallel with the input RF deck bypass caps. These are 0.15 uf X 4 caps = 0.6 uf.  So, use a 1uf cap for the filter C3 position and allow the other 0.6uf to come from the RF bypass caps at the foot of each output transformer.

Use the picture I posted in this thread to see how the filter is wired and laid out.

T

Here's the completed and working VFO. I added a digital display and it works FB.  

The top and side covers of the VFO have been removed for pics. Easy to service and seems stable in all regards. Ready to drive the E-rig with digital pulsed RF.

The second set of pictures shows the VFO output, the VFO buffer output and finally the digital board's output.  I don't like the overshoot that's occuring on the output of the digital board. Anyone know what may be causing this?  I had the same overshoot with no leads attached to the board's output, just terminated with 100 ohms - and I had a short lead feeding the input.   It looks the same at the earlier clock chips too.

This VFO was not an easy thing to get working. I struggled trying to get enuff VFO analog output for the digital board for almost a day.

T

1) VFO out

2) VFO Buffer out as in goes into the digital board.

3) Overshoot/ringing of the final digital output at 12v p-p.  What could cause this?  The carrier sounds clean in the receiver and is stable.

I just tried the digital board with an external sine wave signal generator. The digital board output still has overshoot.  Maybe the sinewave drive needs to be more square/pulse-looking to generate a clean, square output.

T

VFO and splitter/ digital driver schematic-

http://www.classeradio.com/vfo_2_band.pdf

That is truly nasty... !

Tom... please send me the schematic Steve sent you to build the board!

Thanks...

Bruce,

Here's the "Two-Band VFO" schematic I scanned for you.

I tried an HP external sine generator and the digital board output looked the same. So it's not the VFO / buffer.  Does the sinewave have to be squared off to drive the board properly or can a pure sine do it?  I notice Steve talks about adjusting to get a sine saturation waveform.

T

I wondered WHY you posted this schematic link......

Because this link does NOT go with the board!

The one you scanned does...

Pure sine wave up to the base of Q2.

At the emmiter of Q2, it is clipped...

Not at all what your scope pattern shows....


Your last two pictures should look very much like the two pics at the bottom of this page...

http://classeradio.com/vfo.htm

But no... the sine does not have to be squared off....

You basically just need about a 3 volt positive pulse to clock the flip-flop.

Anything negative will be wasted to ground via a resistor.

Sumpin not right in the set-up Tom...

Hi - here is the correct schematic, and a link to the same  8)

The oscillator section should produce about 3 volts (or a bit more) - sufficient for a logic 1, and enough to drive the first flip-flop.

Link: http://www.classeradio.com/vfo_2_band_rev_c.pdf (http://www.classeradio.com/vfo_2_band_rev_c.pdf)  The old schematic on the class E web site had also been replaced, since we have the new one.  The old one is completely valid, but the new schematic goes with the boards that I made.  Note: the next board rev will contain *minor* revisions, so a new schematic will be available for that one.

Picture:
(http://www.classeradio.com/vfo_2_band.jpg)

The input will not affect the output waveform unless the input is causing the flip-flop to unlatch due to ringing.  It is hard to know if the waveform REALLY looks like that, or if this is a measurement anomaly.  I say this because all fast edges shown in your pictures appear to have ringing.  Can you look at any fast edges cleanly?  check the output of the 74AC112.  What does it look like?

Is that measurement right at the board itself?

I have found that the SLIGHTEST inductance in the measurement system (the probes, grounding, etc) will cause ringing where none is actually present.  I have build a number of these VFOs, and the output is a clean square wave.  This is what I get:

(http://www.classeradio.com/vfo_output_waveform.jpg)
Ignore the high duty cycle.  It should be more like 30 or 35%.  The important place to measure the duty cycle is at the gates of the RF amplifier MOSFETs.  It should be about 40% to 45% THERE, which means it will be smaller at the VFO because every IXDD414 adds a bit of storage time!!

I use a Tektronix 475A with 100mHz Tektronix probes.

As an aside, I have some 20 foot runs of coax (and some much shorter) running from the VFO to various transmitters.   Even the output at the far end is quite good, so it should be excellent at the input side.  I put a selector switch on my VFO, allowing me to select between up to 5 different RF amplifiers.  I got tired of disconnecting cables when changing transmitters  ;)   That's a nice feature to have!

Sorry you had trouble getting the oscillator section of your VFO to produce enough output (reference from a previous reply to this thread).  Your experience is not typical  ???  Did you finally use 2n3904 transistors (as specified in the design) or continue with the 2n2222?  Both should work, but the 2n2222 has a higher input C, and appears to be a little slower, so some values might need adjustment.

Regards,

Steve

fwiw, and I am not sure it is an important point, but apparently there is significant difference over time in the 2N2222 transistor!
The early metal can ones apparently are best, and have better specs than any of the later plastic paks. The PN2222 is allegedly actually a different transistor physically (inside, the way it is made), as are subsequent ones marked 2N2222...

                        _-_-bear

That's my understanding also.  I don't use the 2n2222 myself, but Tom did (at least at the start) in his VFO oscillator.  I like the 2n3904 for a number of reasons, but particularly because there is a good compliment - the 2n3906 - which I use all the time in conjuction with the 2n3904.  They are also really cheap and plentiful  :D

Thanks for all the replies.

Steve, I will try some different scope probes and even try a direct, short wire to the scope just to make sure it's not adding to the waveform ringing. It COULD be the probe and I'll see some improvement which will indicate this. I see the same waveform throughout the whole board.  I did notice this false ringing effect when measuring the PDM waveform of my old 4X1 PDM pulse. It was all in the test setup and the pulse was actually square. We'll see later today.

I am using a 2N2222 for the VFO osc and a 2n3904 as the buffer.  The VFO sig is pretty good at 12v p-p, but the buffer drops way off.  I'm out of 904's but will try one for the vfo osc as soon as I get one.  Right now I am getting barely 2.2V out of the buffer to the digital driver board - the bare minimum to keep the digital board and relay circuit happy.  But the real problem with the ringing is hopefuly the test set up.

Otherwise, the VFO is working FB.

I'm testing the shutdown board and power supplies now. Actually, the whole 24 pill rig is to the point where I could JS clip lead it all together and fire it up, but I decided to test it all one component at a time.  The PDM modulator and RF deck need to be tested next.

I'll post with results later.

T

What a difference a probe makes.

I tried two different additional probes. The first pic uses a Tek 6027 UHF probe and the second uses a Tek HV probe.  The difference from the original waveform pics yesterday is big. Looks like that other Tek probe has inductance.

The third pic shows the VFO buffer output.


It appears the duty cycle of the digital board output is around 30% or so?


Pic 1:  Digital board output probe 1

Pic 2: Dig board output HV probe

Pic 3: VFO buffer output to Dig Board probe 1


BTW, a straight wire probe (no compensation) was the worst.


I still need a little more buffer output to play with the VFO waveform pot. Right now it's on the hairy edge of just enuff voltage to drive the digital board. Any waveform compression and the digital board drops out.  Maybe using a 2N3904 in the VFO osc will help - when I get one later.


Looks like everything was FB all the time.


T

So how do these probes look on the square wave calibrator output?  Make sure the compensation cap is adjusted properly in the probe or neither will give you a true picture.

If you are using a Tektronix P-6015A (or similar) the compensation setup requires several steps.

To precisely set the compensation, use delayed sweep to expand the critical points on the square wave calibrator signal.

Of course you want to make sure your built in scope calibrator is doing its thing first so take a look at it with an X1 probe.

Tom,
Why do you have the duty cycle set so low? The two pots on the board should allow you to get closer then 50%

I want 99% final efficiency like some of the class E guys have.... ;D

 Actually, Steve sent me fixed resistors instead of pots for the duty cycle adjusments. I figgered they were optimized, but looks like I will have to dick around with them.

T

Do you have the correct frequency coming out? You could be double clocking the flip flops with internal noise.

Yep, the input to the board is 7770 according to the counter and scope.  The output is 3885 according to the scope and counter. I hear the carrier loud and clear on 3885.

I double checked it with 7770 from an HP sine RF generator instead of the VFO.  I think a little adj with the duty cycle and some more VFO output and I'll be there.

T

What?????????  If you got fixed resistors, they were supposed to be pots.  You'll have to remove them and I'll send you the appropriate pots.  That was surely a mistake!!!!!!!!!!!!!!!  You *must* have pots.  The duty cycle has to be adjustable.

On the duty cycle:  The duty cycle coming from the VFO on 75 meters will be lower than 40% - even closer to 30%.  This is because the IXDD414 drivers in the transmitter add a bit of delay and tends to stretch the on pulse.  I've run a lot of experiments, and for optimum efficiency a duty cycle of 40-something (40 to 45 percent) is best at the gates of the RF amplifier MOSFETs.  I think I'm running about 40% on my rig that's like Tom's, although I'd have to measure it to refresh my memory.

Sorry about the parts mix-up.  I have already modified the parts list to call out 2k pots instead of 2k resistors - that's why the problem happened.  The word POT was omitted from the parts list. That's what field tests are for  8)  (and Tom is a field test site - the VFO kit has not been officially released).

Regards,

Steve

Sounds like the flip flops are working fine. Now you just need to fix the duty cycle.

Tom when you remove the fixed resistors stick a tooth pick in the hole while the solder is soft so you can get the pot leads in.  This way you won't need solder wick and have the chance of damaged pads or traces. You can sharpen the tooth pick to the right diameter.

OK Steve -

No problem.  I'll wait for the pots.  While you're at it, please slip in a couple of 2N3904's and I'll swap the 2N2222 in the VFO too.  Then I'll play with the gimmick cap and the 8.2K feedback resistor to try for more output.


That's a neat idea to use a toothpick, Frank. I usually use wick.  But these boards are pretty rugged and I've never lost a trace with them yet. The plated thru holes are FB.

T

wick works fine if you can get it in the right position without over heating the board. I find boards take less damage when you just open up the hole to insert new component. The excess solder just becomes part of the new joint.

I blow em out with a Rat-Shack solder blowin' iron...

Supposed to suck.

but it blows betta.

That's what I use, too.  You can remove an IC from a board and not damage the etch in any way.  Works great !

The right tool for the job is always a joy to use.
Love my HAKKO 808 Desoldering Gun.
(http://www.hakkousa.com/AHPDirect/images/s808.jpg)

rubber bulb Solder suckers  generate a lot of ESD. We threw them away at work about 15 years ago. wick is much safer.
A commerical solder sucker is fine as long as it is esd rated.

So does the dry air from the woodstove...

All the ground pins cut off the soldering irons...

Metal workdesk....

Cardboard to lay the pcb on while soldering.

ESD   CAN ruin some certain parts...

Doesn't happen very often in the home workshop.

Never here that I'm aware of.

So why get over-worried about it?

 ;D

Is this the Radio shark gem you guys are talking about?  Not bad for $10.
http://www.radioshack.com/product/index.jsp?productId=2062731

That Hakko 808 looks quite nice in the ads. It's $200 on eBay.   I wonder what size tips are used for PCB work like the e-rig boards?  There's lots to choose from.

Steve, do you use the RS unit to suck the solder out or blow it thru like Bruce mentioned?


I bought a bundle of Wick on e-Bay a few years ago. Thought I'd be set for life. Turns out the bastard sold me a slug. It was plain copper shield with no flux in it. Tough to use. QC reject... :-[  Hmmm... maybe I can soak it in some.

T

That's the baby !  Works great  8)

I've seen my share of blown parts due to ESD. It is a very big problem in the modern world. I never handle any HPSDR hardware without a ESD strap. Some guys have blown parts by not using the right equipment.
I've even seen RF fets like MRF150s damaged by ESD.
We get trained every year on ESD. We even recorded SEU events in our hardware. Not a problem with a 6146.

Thats the one!..

Been using this one for 15 years plus....

Darn near ready to fall apart!

But still blows good! :o

Tom,

what value resistors do you have on your inputs to the IXDD414's ?

On the 2-band VFO driver board?  There are none. Check the schematic on page four of this thread.

T

on my last job, getting caught with a board in your hand without your esd strap on your wrist and plugged into the mat on the bench OR wrapped in a ESD bag was a termination offense after the 2nd action. They let you have one chance, after that you was gone escorted out the door.

I'm guessing Bruce meant the IXDD414s at the RF amplifier that drive the RF MOSFETs.  There should be a 300 ohm resistor at the input of each IXDD414, and when combined will form a 50 ohm load (this is done for both phases).  Unless I missed something in the implementation and there are more than 6 IXDD414s per phase..

Yes, I'm using the 300 ohm resistors as per the design for 24 pills posted back on an earlier page here. This equals 300/6 = 50 ohms load per phase.  (One 414 per two fets)

Steve, I'm testing the power PDM boards now.  That floating charge pump is confusing. Can the modulator be tested as a stand alone unit considering the floating ground and charge pump?  I have a good signal going into the opti-coupler but nothing coming out at pin 5 - and the charge pump regulator is not regulating at 12V, but instead showing 16V at real ground or 0V at floating ground.   The charge pump seems to be the issue.  How is the unit tested in light of this or am I missing something?

T

Correct me please Steve if I'm wrong but... 
With nothing connected to the modulator output there appears to be no ground return for the floating supply regulator. The RF deck would be the ground return in operation.  For test purposes I'd tie the floating and real grounds together with a 1K 10Watt resistor just to get that regulator biased on.

Correct  8)   Tom, you can test the modulator drivers, etc. by simply grounding the output of your PWM filter (or the output of the modulator board).  Obviously, no hi voltage can be applied to the modulator !!!!  This will bring the charge pump diode into conduction, and the power supply on the PWM output board will function properly.

There's a nice feature of using the charge pump approach - if there is no load on the modulator, it doesn't produce any output!

You can also check it with 12 volts on the drains from the LV supply just to see it function. bootstrap driver takes some getting use to but they function well.  We used them in the F111 weapon system release drivers because N channel FETs had lower RDS on back in the day.

Yes, I now see how it functions.

I grounded the floating ground and both PDM power boards worked FB.  Nice square waves at the FET gates with almost no overshoot. I'll wait until I put the transmitter together to test the drains/outputs, etc.  TNX!

Well, I just cleared the bench and put on the 24 pill RF deck for testing. This is the last component before wiring it all together and then getting the many T/R and sequencer functions working right.  Then time to breathe life into Rico Suave.

T

"Clear!"


 ;D

Hooked up the 24 pill RF deck today and fired it up. I saw good pulse drive thru the 414's into the final fets. I put 15V on the final MOSFETS and saw output into a 4 ohm resistive load.  However, my outside RF connections were clip leads - long and JS for the input and output so I saw signs of parasitics.   Otherwise everything worked.  This is good.

I'll do the final tests on the RF deck when it's properly hooked into the tank circuit and has shielded input cables, etc.

So, everything has been tested in component form and works FB as far as I could test.  This includes the HV supply, PDM generator, PDM power boards, shutdown board, VFO and driver board, RF deck, smaller power supplies, sequencer, metering, T/R switching and tank circuit.

Now on to mounting, integrating and final troubleshooting the various components to make Rico Suave a real live rig. 

T

Houston....WE HAVE LIFT-OFF!! :o

heheheh... no lift-off yet, Tina.   The major components are still scattered all over the shack needing to be mounted in the rig and wired up together. It may be another two weeks before first light.



Threading the wires thru the cores - output transformer layout:

Here's the PHASING diagram to hook up the output transformers to the fets for a 4 module (24 fet) rig.  The two left modules are fed at 0 degrees and the two right modules are fed at 180 degres out of phase. This phasing arrangement can be used with either a digital gate drive or analog gate drive configuration.

The drives marked "0 degrees" or "180 degrees" go to either the 414 driver chips or gates of the 11N90 MOSFETS.  

In my case, the four primary wires marked "Drains" are #10 wire (one loop for each of four modules) and the one secondary wire marked "tank" is #6 wire, (one wire threaded thru to combine all four modules) -  although these are not critical wire diameters.


This physical phasing layout info is not clearly shown anywhere, so print it out if you plan on using this general rig plan.

T




Attached Below:

1)  Diagram of output phasing

2)  Picture of the actual output transformers: (BTW, in this picture, two of the the output transformers are wired incorrectly. Refer to the diagram for the correct wiring... ;)  )

The meter polarities are also wired backwards in this picture. That's what initial testing is all about.

I would have swapped #3 and #2

To help balance.

Bruce,

It's simple enuff to change it.  Please elaborate about the effects of balance.

I did it this way to keep the drive areas segregated on each side of the heatsink - no other reason.

What might happen if I left it the way it is?

T

The secondary lead is so long I don't think it is worth the trouble.

Oh I;m not real sure Tom...

Just all the diagrams I've seen do it that way...

0deg, 180deg, 0deg, 180deg  etc...

your "0 deg" phased modules are 2 transformers away from ground end...

Thats the only real reasoning...

Frank or Steve would be the ones to ask for sure if it makes any difference at all.


I've found that usually if there is any unbalance between phases, you can almost guess that the module who's transformer is closer to ground is the one drawing slightly more current.(or was it the other way around?)

It doesn't matter about the phasing.  I do it - 0 deg, 0 deg, 180 deg, 180 deg in my transmitter to keep the leads shorter.

Works just fine  8)

Here's the latest shot of Rico Suave almost wired up and ready to do some initial testing. All the components have been individually tested, but working together is another thang.

All these wires are DC/bypassed, so length is not a problem. I will tie wrap and neaten everything up later, once everything is mounted inside the cabinets.  

Pictured are the VFO/Driver, shutdown board, sequencer, 12V supply,  +- 18V supply, HV supply, PDM generator, PDM power board and RF deck.  (PDM filter not pictured)

I will later be able to easily pull everything out for servicing, just as pictured. I am not bolting down any modules. They will be bonded electrically.

T



There's a lot to building a 24 pill class E PDM rig! Don't let anyone tell you it's easy the first or second time. It takes lots of time and concentration. Despite having the nice PC boards, it's no Heathkit... ;D  But well worth the effort.

While we were taking E-rig pictures, Fabio started mumbling about getting some attention. Notice his slight green hue.

Included is Fabios new SS MOSFET audio driver designed by Frank/GFZ.  It's now safely mounted under Plexiglas.

Also see Fabio's 3-diode circuit high level limiter I've been fussing with lately.

T


Pic 1:  Look closely for the ghost reflection of the GFZ driver board.

Is that 10 FETs in the PDM modulator output?! What are you planning on modulating after this is built, a second bank of 24 and combine them???????  That's quite a few amps of modulator you got there Rico.

Yep, Mark, if I can find more room for a second PDM filter and squeeze a second RF deck in there, Rico has the chance of becoming a 48 piller.  It's been in the plans since the beginning. We'll have to see how the rig runs at 24 pills first.  There's already a 40 piller out there and I've heard  of plans for even bigger stuff in the wind, so gotta keep up with the E-Jones, caw mawn... ;D

T

The gods must have planned some fun for me tonight. Talk about rotten luck and life not being fair sometimes...

Rico Suave is almost all wired and ready for full RF testing. All the infrastructure and outside whirl connections are ready to fire him up. The modules are still spread out, but easily placed into the rack intact, once tested.

Anyway, I had the power off and was snaking my RF deck cables to the VFO/Driver digital board to connect up. This was one of the last items before firing it up for RF.  Suddenly I heard a big snap and smelled smoke. Yaz got up and wanted to leave the room.  The exposed ends of my RF deck driver input cables had brushed against the 240AC terminal strip on the back of the rig. I had forgotten to unplug the rig.  I was Yallowfied!

At first I figgered it was nothing, but then realized the two cables went directly to the twelve  RF 414 driver chips. I did an inspection and found six of the chips were burnt and broken up with soot on the heatsink. Who knows what else got wasted? The many bypass caps, the twenty four MOSFETs fed by these driver chips?  I don't mind an RF crapout, but to lose them from a space-out like this?

After a couple of hours of tight work testing all the solid state devices I found just one half of the RF deck was affected and the other half was OK.  Fortunately the MOSFETS were still OK, but assorted components with the six driver chips had to be replaced.

It was really rotten luck cuz I had already run the cables and decided to reroute them again to make it prettier.  The only good thing I gained is the confidence that the rig is servicable when these things occur. Usually RF decks can be a real pain to work on.

I fired the system up and found good driver RF at the MOSFET gates. Tmw I might try some HV on the finals and see what happens.


The moral:  Double check to be sure there are no exposed voltage points (including 120/240) when you think everything is shut off.... sigh.   I plan to put a plate around that terminal strip tmw. I already added 18V transorbs to the RF deck input. That may have saved it in the first place.

T

<<snip>> "There's a lot to building a 24 pill class E PDM rig! Don't let anyone tell you it's easy the first or second time. It takes lots of time and concentration. Despite having the nice PC boards, it's no Heathkit...   But well worth the effort." <<snip>>


Not to mention the $10,000.00 worth of crimp on wire ends and hook up wire!!  ;D  ;D

Tom,
First, really sorry to here about the lab accident.  I know from whence you speak and feel your pain. It especially smarts when you know it was avoidable. UGGHH.  Still happens to me now and then, but I'll refrain from publicizing such events. All success and sunshine here at QFX labs!  Yep,... wanna buy some swamp land with that?


I noticed you are using 32 beads in your output. I went around a while with Steve on this and settled on 64 at a minimum for 24 pills. You might want to check with Steve again since he did those calculations.   If 32 is the right number maybe I'll consider 48 pills! 
Later,
Mark

What a drag Tom :( I know from mistakes. Try not to get too discourage and move on. I have had to learn patience with the current project. I tend to be compulsive and want my project finished; but the slow pace is due to the detail work. I get frustrated cause I want to get MM on the air. Mark has the patience of a saint when it comes to the detail work. I finished the wiring on the triode and driver board yesterday. Everything in the pressurized tube assembly is finished. I'm waiting on meters and a few part to finish the tank, band switch etc. The biggest part of the project is milling the supports for the vac caps for C1 and C2; and the gear and chain assembly for the sub band switch (driver band switch). These will be made out of 3/8 aluminum plate. We have critical spacing due to the fact the parts are so large and have to maintain 1 inch spacing to keep B+ from jumping to ground etc. What seemed like a large chassis quickly becomes crowded once you stuff it with part.
Let me know when Rico comes on the air so the farmers in CT can wrap foil arund there sheep. ;D

you  want to shoot for 150Gauss per bead for low loss.
I used 16 type A material (ui=600) in my push pull 22 fet final.
They might get luke warm after it sits at 48V/1200 watts for 5 minutes on 75m so 8 per stack sounds good for me.
My 160 meter rig running at 80 volts I have 10 beads type a material for a push pull final. I've never felt them warm up running 300 watts carrier and it will do almost 200% positive peak. This rig has been on the air since 1996.
16 beads per stack would support a high voltage. I think it is a bit much.

Ouch! Glad you and Yaz were uninjured. Don't want to see you on the local action news!!!!

I just love "wireless" communications!!

Thanks for the get-well greeting cards, guys... ;)

Thirty-two cores appears to be enuff, Mark. That's what I ran with the other 20 pill rig six years ago - no heat after an OB xmission.


Yep, this stuff can be real fragile to mistakes. It will run forever once running, but cannot take random shorts or external voltages inserted into it's inner workings... ;D  The tube stuff will usually survive.

I try to make everything servicable. This means running longer harness wires that will permit the boards to be flipped over easily when in-circuit.  I also cut square 16" X 16" holes (with access doors) on each side of the cabinet for inner access. I can actually replace FETS on the RF deck without pulling the rig apart.  I'm tired of building with things cramped and impossible to get at. Some day we old buzzards will not like the twisted positions needed to get at this stuff.

Might make some more progress over the next few days if all goes well.

T

Hopefully there are still guys following this old thread and thinking of building up a big class E rig. We're getting near to the end of this project with testing to follow. Hope you all have enjoyed riding along.

Well, had a few more problems today.  One of the shielded cables shorted that goes to the input of the PDM modulator. I had heated the inner conductor too much and it broke thru the insulation.  This caused my PDM 414 driver to short out. I went through two drivers before finding the problem.

Got the whole system to key up smoothly with the sequencer. There are about eight relays that kick in. The big 12V coil primary relay arrived today and worked beautifully.  All levels from the VFO on up are within specs.

We're now at the point where there is gate drive to both the RF deck and PDM modulator. All systems appear to be working except for the high-current shutdown part of the shutdown board - I'm awaiting a new chip from Steve for that.

So, tomorrow I hope to put the HV on and see what I have. It's been a slow process with lots of minor issues along the way to get to this point.

Here's some shots of the rig cobbled together ready for a test. The cables to each module are intentionally long so I can pull each module completely out of the cabinet to work on. It still needs covers and dressing up. I will test and perfect everything first before tie wrapping and making the wires look good. I expect to be pulling modules in and out for a long time yet during testing and troubleshooting.


Notice the side cabinet access for the RF deck. This will have a door later on.  Also notice the two layers on top - the control circuitry on top and the PDM modulator below.  The RF deck sits in the bottom of the cabinet. There is room to add another 24 RF pills next to the first RF deck.  The bottom of the rack holds only the RF deck and tank circuit, so there is room to play in there.

T

Here's one of the cooler shots. Notice the schematic and glasses in the background. Just like a how-to magazine... ;D

Hmmmmmmm.. I just noticed a couple of things that you may want to consider fixing before attempting normal operations.

There appears to be a "driver bus" rather than individual coax cables running to each IXDD414.  This did not work in my own transmitter.  It works OK with 4 MOSFETs and 2 IXDD414s per side, but when I went to 6 MOSFETs per module with 3 IXDD414s, there were parasitics caused by the long, unshielded driver input bus.

I corrected the problem by running an individual coax cable to each driver, with termination (300 ohms in this case - 6 devices per phase).  I would recommend fixing this.  Also, do ground the shields at the driver coax cable common point - where they all come together.  It should resemble this:
(http://www.classeradio.com/12_fet_closeup.jpg)

Second - hey, what's all that extra wire connecting the output transformers???   ::)  This will surely introduce inductance that's not supposed to be there.  The primary and secondary wires should all be exactly the same length for each transformer, and be as short as possible.  Similar to this:
(http://www.classeradio.com/topview.jpg)

The transformers started out like this:
(http://www.classeradio.com/step10.jpg)

The shunt capacitors are way over at one end of the drain bus.  They should be in the middle, or use 2 capacitors of 1/2 the total value and put one at each end.  For 160 meters, you can add additional shunt capacitance at the end, as long as this is not the total capacitance of the shunt capacitor.

The entire transmitter, with all the construction steps is shown here:
http://www.classeradio.com/24_fet.htm (http://www.classeradio.com/24_fet.htm)

Tom,
I have also had problems as I told you with parallel drivers going into weird oscillations as they ping -pong against each other. I had a LF oscillation in my 160 meter rig when I first built it. A long cable feeding the drive needs a good load on it. The shielded wire you are using looks like about 20 ohms impedance so you may get away with parallel drive if you load each end of each bus with a low value resistor. You need to take a careful look at the drive to make sure it is stable before you add drain voltage or you will be replacing parts. Steve's method of multiple drive cables reduces the drive impedance but adds complication.  Your predriver can handle some current so you might get lucky adding load resistors to clean up the pulse. A small series resistor at the pre drive end of each cable will reduce reflections at the expense of a bit less drive voltage. 

OK - Thanks for the suggestions, guys.

It's close to firing up, so this is good info. I put a simulated 1.75 resistive load on the input tank and tuned it to give MFJ analyzer 50 ohms on the output, so that shud be a close start.

Yes, I was aware of the bypass caps being on the end, Steve. It was a matter of servicability and crowding in that caused me to do it. But guess I'll move them to the center now, since I got caught.

The same with the feed cables to the driver chips - I wanted to simpify things, but maybe I'll try doping it more as Frank suggested.    Frank, what value series predrive resistor?  10 ohms or something like that?  Or since it's on the table, I cud always run extra cables and do BOTH.

As for the longer primary xfmr leads - they needed to be longer cuz of the physical position of the transformers. In the old E rig, I did it like yours and servicing was a nightmare cuz the transformers were right over the fets. I'm hoping the extra 2-3" will be forgiven on 75M....  ;D

Do you think firing it up with the PS at 1/2 voltage (~ 70V total, 25V on Mosfets) will prevent fet damage if I have parasitics or shud I go even lower by adding a test Variac?


** I'll do the mods and take a picture and post it before firing up.

T

Tom,
Adding any L in a low Z circuit adds ringing so be aware of that.
Make sure the gate drive is clean before you put any voltage on the drains. Also make sure the the signal on the input of the drivers is nice and square. I would set the PDM generator output to a low voltage and work your way up to carrier. I would modulate at each output voltage to make sure everything is stable.

Hi Tom,

There are some simple things you can do to improve the situation without changing the basic layout.  First, I would really make changes to the output transformers.  This should be a simple thing, but those long lead will cause problems.  You may not even be able to balance the modules correctly.

So, some suggestions.  The RF output doesn't have to come from the center of the bus.  Because you are dealing primarily with fundamental frequency (and not lots of harmonics like the shunt capacitors handle), it is not as crutial to take the output from the direct center.

Given this, and knowing your layout, you should be able to bring the transformer primary within 1/2 inch of the drain bus and connect it there.  The bypass capacitor should be similar - maybe 1/2 inch of transformer primary and short leads on the bypass caps.  Come of the ends - just make the leads SHORTer.

The secondary should be dressed to be as short as possible between transformers.  At the ends, it's not as critical.  You don't want a lot of phase shift along the line between the modules.

Anyway, some ideas.

Regards,

Steve

OK, Steve and Frank -

Yes, I wondered about using the end of the bus for the pri connection - will do and make them shorter.

Maybe I can tighen up the sec between transformers somewhat too.

I'll make all the changes mentioned in the last few posts and post a close-up picture later.

I can't fire this thing up until Monday when I get that LM-239 chip anyway. I'm also adding the 100A and 200V digital meters today. That shud finish the construction - at least until I get beat up during testing time... ;)

Thanks.

T

Steve and Frank -

Here's the mods I made.  There are separate cables per driver, the bypass caps are near the middle and I shortened up the xfmr primary connections to the end of the bus.

I can see now how the predriver input bus was facing the output busses of both the driver and gates of the fets, creating a possible feedback loop. Now the connections are smaller and shielded better.

I didn't add any resistance in series with the pre-driver cables yet. If I have parasitics, that's the first thing I'll do.

Watsa?

T

Tom,
I would have run the cables back to the predriver chip. Now you have a bunch of 20 ohm cables hanging off a single cable. Big Z bump. Maybe you could add 2 driver chips where the terminal strip is located if there is a degraded pulse at the joint.

Frank,

The VFO output uses a 414 driver chip and has four foot long cables going to the rig. After doing the mods, I see no difference in the RF drive waveform. The waveform at the predriver chips in the rig and at the gates of the MOSFETs looks very good, like a class E waveform. I see little signs of deformities, so guess we're all set.

Tina said his E rig burned up tonight becuz of an RF parasitic... so guess it's something to be careful of... ;)

I will take your suggestion of slowly ramping up the voltage of the PDM pulse to test the finals at a low power level.

T

You want to drive the gates with a square wave which will degrade a bit when you add drain voltage miller effects.  Long leads cause ringing there is no hiding from that. Remember what I said about the source leads. Everything matters.

Hmmm.... I looked at the 414 output from the VFO when disconnected and it's a nice squarewave. But when I hook up the 4' cable going to the rig's input the waveform looks half way between a sinewave and squarewave. (like a class E waveform)  

Steve mentioned he runs up to 20'? cables from the VFO driver output to the rig. What does yours look like at the rig, Steve?


My old 20 pill E rig using analog drive waveform looked like a standard call E waveform, cuz that's what the driver was.

So, how much will the efficiency change by my using this E-waveform  as compared to a squarewave? Will it make it more prone to parasitics cuz the on time is higher?

I can't see how adding a 414 at the rig input (after the 4' cable) will help cuz I already have one driving the finals 6" away and that helps clean up the waveform very little into the MOSFET gates. ie, It's still basically a class E waveform at the RF final gates.

I'll try some load resistors at the input and see if that helps clean it up. Hopefully there is plenty of current capability in the 414 driver.  I have little heatsinks on them now.

T

The harder (more square) you drive the gate the better it is.

After effecting a boatload of repairs and upgrades in the smaller rigs; inside and out (antenna repairs), Murphy bit me in the arse :P I lost a couple of fets in the big rig. I have been meaning to upgrade to digi drive and install Steve's overload protection circuit. I am populating a new heat sink and tearing down the old project for a complete overhaul. As if I don't have enough projects already. :P

It's all about layout

Brent,

Will the shutdown board protect against parasitics?  I doubt it. Except for no VFO drive, it just senses DC current and has no idea what freq it's at. Maybe it wud be wise to add in the swr input. That might do it.

But, if there is no load at the parasitic freq, big voltages can occur....  what do you say, Frank?

Yes, hopefully the digital drive will make the whole lash-up more stable. I'm about to find out here myself.

I'll try the load resistors later today and see if it gets better.

T

The HossTraders Manchester, NH WX has finally cleared out a hi-hi FB sunny gap for us. Thur, Fri always looked good. Sat was questionalble, but looks good now!

T

No Tom, but at least the pulse train will shut down faster than the old overload circuit....the digi gate drive is the biggest benefit. The old 2 fet analog driver stuff was always unpredictable. I am adding shunt resistors on the 40 meter deck and running cables like yourself to each driver chip. Since the small deck is 10 fet, I will use 250 ohm terminations per cable.

I am trying to track down and odd problem with the 8 fet 160/80 deck (also digi drive. I noticed a slow change (maybe thermal) in current draw between the modules as the deck runs for a bit. Starts out 4 amps per module and then creeps to 4.5 and 3.5 per module? I have 1000pf atc chip caps as shunt in the center of each bus. I changed out the doorknobs to ATC's to see if it was the problem. I am measuring about 375 volt peaks on the drains.
Any Ideas Frank...Steve?

Brent

Just make shorter transmissions... ;D   

When you blew out the RF module, what did the waveform look like on the scope - did it have the normal hairly fuzz of parasitics look? And how many seconds did it run like that before blowing? 

I tried mine the other day without the latest mods, but with a 2 ohm load on the RF deck and saw parasitics.  I used only 12VDC, so no damage. Hopefully everything will be tame when I test it soon. I just calibrated the shutdown board, so getting close. I decided to add swr sensing. I have an old Bird slug set up that I can keep in reverse and sample some voltage for the board.

T

Wasn't watching Tom. Just the typical shotgun effect and a blue flash. I can't really confirm the parasitic issue, but its a likely due to uneven pep drive voltages of the past. Was just talking with Al W1VTP and BANG!
Since Mark is building similar rig...I will construct rf deck when he does his. In the mean time I still got Baby E to keep me on the band. ;)
B

Just pulled up one of my class e final simulations and added .1uh in series with the drain lead of 1 phase. The drain signal went from nice and clean to high frequency ring on both turn on and turn off. This adds a lot of extra dissipation in the device die and reflects this crud back at the gate. If this crud is generated at the switch point the device oscillates around the switch point making it unhappy. Driving the gate harder helps overcome this problem but the real fix is layout reducing leakage inductance and strays. 
So if your layout looks like it fell off the back of a cow I wish you luck

Heck, no problem.  If it blows up I'll use the parts to build a GFZ Joystick.... ;D


In the meantime, I'll pull out the output transformers again and make them more compact with less wire.

T

More improvements:

I stacked the cores tightly and was able to take about 7" off the secondary and about 2" off each primary winding.  The only extra lead lengths now are the 2"  primary connections to each drain bus. The bypass cap leads are about 1/2" to each capacitor.

I also added some .02 disc caps to the transformer bypass caps for good measure.

That's about all I can do to shorten up the output transformer.

Got the digital blue 100A  and 200V meters working. Look pretty.

Still need to build a high swr sense circuit.

T

Just FWIW guys,
                       I designed and built a stripline IPA for my 220 repeater some years back. (I used an NPN bipolar device, dont remember the number) I was popping the tops off of pills right and left. I found that it would go into a parasitic oscilation whenever and only if it felt like it. I bypassed the 12v feed at the end of the stripline six ways from sunday and it would still do it occasionally.  I found that I had to bypass it for many different frequencies. I wound up using a 100pF, a .01uF,
a 220uF electrolytic, and are you ready for this..............a 1N5400 series diode.

The diode is what really did the trick. The diode really did the trick, it just tamed it down and stabilized it so well that it has been now running for close to 15 years without a problem. I guess slicing off the negative half cycle prevents it from going into full oscillation. Whatever it did, it now works FB.

I wonder if something like that would work for youse guys??


                                                         The Slab Bacon

Tom,
I'm concerned with the drain lead to the transformer could be as high as .050uh. Also you could flip the phase of the secondary to get shorter leads to the tank circuit if that helps. The joy stick layout is a bit anal. There are other ways. to get shorter leads.

Slab,

Good ideas. I made note of using extra varied caps and the diode. If I have problems I will add those items to the two supplies in the RF deck.

Frank:  My other 20 piller had a similar layout and worked well for nine months until I pushed the drain voltage up too high... :o

About those 2" pri leads... if I have problems, I will replace the wires with thick brass bus bar right to the transformers to reduce L.

T

Frank,


Please take a look at this schematic of the shutdown board. I want to drive the shutdown board with an external Bird rev slug for high swr protection. To the extreme left shows the  swr sensor inputs marked  "optional external inputs."  This is a balanced input to a LM-239 chip.  My Bird slug in the reverse swr mode will put out maybe 0.3 volts max positive voltage. I tried hooking it to these inputs many ways, but the high swr .3V will not trigger the stage no matter where I adjust the "external threshold" pot on the LM-239 stage. If I put 5 volts to the  input,  it triggers OK.

Shud I use an external transistor or op amp to amplify the 0.3V DC bird signal? The Bird output is unbalanced.  Since it needs DC to work, this is more complicated.  Can you come up wid a simple circuit to interface?  TNX.

http://www.classeradio.com/efficiency_meter_rev_d.pdf

T

Take the bird positive and connect it to the negative input. Then take the bird negative and connect it to the positive input. Then adjust the pot for the trip point you want. If that doesn't work you will need to change some resistor values around the comparator.

Tom, If it helps here's a peak amp I built up, and am still using, for element powered wattmeters.
You can remove the diode and cap in the peak detector to drive your comparator inputs.
You could even use the forth stage as the comparitor.

That's what I tried last night and NG.


What resistor values would you change to make it more sensitive?   Actually that board is so tiny to work on I'd almost rather add a transistor outboard as an interface gain stage.

Thanks for the schematic Buddley.

T

sorry I told you to connect the bird backwards. Plus to plus and minus to minus. Remove R732 to eliminate the voltage divider on th epositive input

I built up a single 2N3904 NPN transistor circuit that amplifies from 0.3 to 5V.  That shud give it plenty of drive.  The DC output is 0-5V.


I'll test this circuit in operation later and post how it works out.

T

Not to hijack the post, but I found the problem with current drop. Was a bad driver chip (IXDD414) in one of the banks. Also got the 40 meter 10 fet deck upgraded with coax distribution and termination resistors to the driver chips...had the deck on the air for a couple of hours and rock solid! ;D

Tina

Good going, Tina!

That's a good thang to know since mine is using the same drive config.

T

HTF did you manage to blow a driver chip?

Long B4 I had the correct amount of shunt and ATC caps. Bad cable to one of the phases etc...

Hey it's TINA!!! He can do it all!

Fired up Rico Suave for a contact on 75M today. Eric made a recording and Joe/PJP broke in with his KW-1 rig. I will have to upload it somewhere else cuz it's 5 meg.

I spent the last week trying to get the PDM pulses out of the homebrew VFO and sequencer board. I'm running Rico at a conservative 1/2 voltage = 250w out for now.

So far, so good. The VFO is stable and the full digital drive is very stable.

I spent a LOT of time bypassing, filtering and shielding various components before all was stable. Thanks to Jay/W1VD who sent me some "chip" capacitors so I could build a "zero lead length" type PC board for the transformer B+ bypassing. This made a big difference and got rid of any parasitics. Those orange drop caps are NG for RF.  I have three 0.1 chip caps per module to ground now.

I added four fuses, one for each MOSFET module. Also added fuses to every PC board for good measure. Notice how clean the transformer area is now that those big orange drop caps have been replaced by tiny chip capacitors.  I went on a days-long campaign adding filters, protection and bypassing bells and whistles. It appears to have paid off in general stability and good operation.  The E waveform looks textbook, but the jury is out until I goose it with X4 power.

I like the sound of the audio, though I am fighting a little hum from a ground loop. The E rig is about 15' in cable length from the audio rack and other gear.

Hope to ramp it up and get on with it more this week.

T





1) RF deck showing new filtering on the drivers and finals

2) Close up of the RF transformer bypassing.

3) More

Shielded cables in and out - and damper diode beer can added to PDM filter.  The beer can helped to quiet down the PDM spikes.

http://www.filexoom.com/showfile-19820/75m_rico_suave_e_rig_k1jj_wa2pjp___wa2cau.mp3

This is a recording made today by Eric/WA2CAU of Rico Suave and PJP. It's in 10KC bandpass. (5KC audio)  I did a brief description of the rig and you can hear the audio quality.

Eric's comments cannot be heard. There are several transmissions combined together.

The file is 5 meg and takes a minute to download.

T

I've been curious, does anyone work on 220 any more?

Ahhhhhhhhhhhhhhhhhh... I see one thing that could be the cause of all problems :-)  The first inductor of the PWM filter, and the first capacitor after the first inductor should be located immediately at the PWM output, and not carried away from the output board at all.  In fact, the inductor ideally should be located away from the remainder of the filter unless your PWM output board happens to be co-resident with the filter.

Once the PWM signal is processed by the first inductor, there will be no spikes to worry about.  But, carrying the PWM signal away from the PWM output board is not a good idea at all.  The PWM output signal is rich in harmonics, and these harmonics are of considerable power.  By carrying the pwm output signal away from the output board, there is also a danger of coupling "around" the filter, due to ground effects, ground inductance and the like.  See how it works, but it might, at some time in the future, be advantageous to move the first inductor and the first capacitor and put them at the PWM output.

Something else to consider with respect to the PWM filter.  This is probably not a big deal, but I did notice it immediately.  It is preferable to bring both wires interconnecting the inductors directly to the capacitors, and then have them go on to the next inductor.  In this way, there is no inductance added in series with the PWM filter capacitors.  The interconnecting wires are part of the inductance of the inductors, but you don't want an wiring in series with the capacitors.  Maybe it's not a problem - but I thought I'd point it out.

WOW I agree. You are switching a 130 volt squarewave. You should consider moving the output board to the filter plate for best performance. You are running a lot of juice through coax cable. I bet it will run warm. Consider pulling the guts out and sliding #8 or #6 in place.
Inductance in series with the caps hurts high frequency roll off. A big deal in tank circuits also.

Overhaul of the old 20 pill deck.
It begins :)

Hi Brent, Looks like a good start !!

I would put another screw, holding the source bus to the heat sink, between each of the existing screws.  Basically, 1 screw per MOSFET - located more or less between them (and at the ends of the bus, of course) works very well.

Hmmm...  That's probably why I had so much trouble filtering out the PDM pulses from the other boards.  I will reposition things to get L1 close to the PDM power borad output. The rig is running very FB at 400 watt carrier now, so the additional filtering I did only helps it become even more stable when the filter is set up correctly.

I'll also modify the capacitor leads between inductors as you suggested, Steve.

Last night after a 2 minute transmission the VFO broke into a nasty phase noise FMing according to the guys. It turned out that the 12V voltage regulator on the VFO driver board was running too hot, despite a small heatsink. I added four larger heatsinks to all the regulators and two 414's and it ran FB afterwards. Those regulators will shut down due to a thermal sensor internally.  I found that all the tabs in the four devices are at ground, so ONE heatsink plate could be bolted on for simplicity.  Tho, separates are better for servicing.

All in all, after a robust one hour on 75M last night, the rig ran superbly. The RF heatsink was barely luke warm and all appears very stable with no parasitics. The VFO is dead solid.

BTW, that 100 pf doorknob on the input of the L1 filter shown in the pic above  - I removed it, as it caused slight ringing in the pulse.


This is alien technology, I think... ;D


Brent:  That's a nice looking start. I see you left room for another 24 pills, caw mawn... ;)  Be sure to bypass the heck outa the vcc 414's bus.  I used several different types of caps there. Also used some input filtering using ferrite cores and bypass caps on the left edge of the heatsink. (see pic #1 above)

T

HF ringing is due to long lead length between switch and first inductor.

Hi Tom,

I reserved comment on the capacitor input to the PWM filter, theorizing you might have had some good reason for this capacitor that excaped me, but since this is not the case GET RID OF THE INPUT CAPACITOR ON THE PWM FILTER :-)  ;D  In fact, do everything you can to MINIMIZE the capacitance in the PWM filter input inductor and output stage.

Yes, do move the input filter inductor and first capacitor following the input inductor.  This will cure many ills.

The IXDD414s and regulators in the VFO / Phase Splitter board MUST be heat-sunk.  I thought this was shown in the documentation, but I'll surely check it.  If you notice, all of those components are at one edge of the board, so you can bolt all of them to a chassis or heat sink.  All are tab-grounded devices, so no insulators needed when screwing these components to a heat sink.

Steve,

I was able to shorten the PDM power board lead to about 6" total length from the board to the L1 input terminal. That's pretty good considering the previous routing.  The lead previously went tnru a terminal strip, thus the longer route. All that is gone now. I fixed the filter cap leads too.


You said to minimize capcitance - but can I still add some shield wrapped around this 6" PDM lead and grounded or will that add enuff capacitance to degrade things?

I did have small heatsinks on the driver board, but they were not big enuff. Now the devices get luke warm with the bigger sinks.


The 100 pf input PDM filter cap was gone as of last night.

T

Hi Tom,

It probably won't hurt anything, but only 6 inches of wire probably won't be an issue.  I don't run any shielding, and the wire running from the PWM output board to the coil is longer than 6 inches.  Since the coil isn't shielded either, I wouldn't bother  ;)

Tom,

Despite the fact that I didn't shield the approximately 8 inch wire running from the PWM output to the PWM input filter inductor - and the inductor itself (air wound) is also unshielded, I don't get into anything at all - anywhere, with the PWM signal.  If you bring an AM broadcast receiver into the vicinity of the rig when I'm transmitting, there is some white noise.  That's about it.

So, it probably won't be an issue with your rig either if you don't shield that 6 inch interconnecting wire.

Steve is there  max length (never exceed) on the output of the driver to the PDM filter? I may rethink the layout when I rebuild the filters.

Brent

Added additional screws to source buss and soldered legs of devices.

Brent,
I would solder the source leads a lot shorter up closer to the body of the part.

Brent,

It may be an illusion from your picture, but are the drain and gate leads clearing the grounded bus bar OK? I almost made the mistake of mounting my MOSFETS too close to the bus and had to sharply bend up the leads to clear. It all worked out, but I shud have spaced them 1/8" farther away.

T

Its an illusion..plenty of clearance. Frank I will redo the solder on source leads. I got the atc caps from Bruce yesterday. I am going to try and finish today. I'm still waiting on the .47pf bypass caps.

A long source lead adds inductance which shows up as negative feedback against the drive signal.

Today's Update:

Installed the feeds for the IXDD414's, transorbs, and shunt caps.

Been an interesting thread.  Thanks for all the photos,  Tom,  Steve,  Brent (and others ?)   Am just now going back and re-reading all.
 Someday will get together my act  and start my CLass E project.

72   Thanks     Vic

Finished Deck!
Minus a barrier strip for 12 volts (VCC rail for driver chips); OK..the relays for 160 :-\

Join the fun Vic....lots of the same rigs being built! ;D
Everyone does a slightly different layout

Brent W1IA

Thanks, Vic -   There will be more posts on the subject.   


Looks FB, Tina.

Brent -  It's hard to tell by the photos, but do you have bypass caps right at each 12V lead of the 414's?  It's important to do this. Caps at the end of the bus are good, but add them to the leads too.

T

Yup...I found some .47's electrolytics  at 35 volts; very small and effective..I installed them next to the leads on the 414's. Also put some small 10 uf electrolytics (orange) at the end of the busses. I may put some .001 and .1 's to round out the values. Very compact design grasshopper 8)

Brent,

Yes, that's the idea. Though, electrolytics are poor at RF. Take a look at my latest RF deck pic above. I stacked .001, 0.1 and .47 disc and film caps together - all connected directly to each VCC pin of each chip.   Frank hammered me to being anal about this.

The other thang is to use quality ceramic caps at the output transformer bypasses. (modulated B+) Get rid of those orange drops. Even using those expensive chip caps there is not overdoing it. I first used orange drops and saw parasitics. After I went with zero-lead length chip caps from Jay, it was as stable as a rock. Look at my latest pic closeup of the PC board I made to hold the 3/8" square chip caps that are better designed for RF.

Also, consider bypassing the incoming 414 VCC main lead from the power supply on the heatsink. And, bypass the modulated B+ at the heatsink for RF. I even slid some ferrites over these leads in addition to the RF bypassing.  (Remember to consider the capaciatnce added to the PDM filter output when adding to the modulated B+ lead if the cap is of significant value)

T

The .15's are mylar film...they ran in the old rig..cool as a cucumber. Ok on the .47's... :( Looks like I will have to replace them

My orange drops ran cool as a cucumber too.  But I had parasitics until I changed them out.

Do a GFZ experiement.  Put one in series with a 5 ohm carbon resistor and then put an RF sig gen signal across them. Use a scope probe to find how much RF divides across the resistor and cap at 3.9 mhz, etc.  If the impedance of the rig is 2.75 ohms, then you want the cap impedance to be < 1/10th = 0.275 ohms.   Is it? You want most of the RF across the resistor in this test. If not, you will get some degree of RF getting into your PDM modulated DC cable and the transformers will not be grounded well for RF = instability... NG.    

Jay/W1VD  has a source for these 0.1 uf chip caps for only about $1 each. Mount them on a PC board like I did and get zero lead length.  I used three in parallel for 0.3 uf total per module.  RF= dead meat.

All this quality bypassing is cumulative. Do everything you can in each circuit and the rig will never let you down in bad situations.

Hey, I'm just parroting what Frank taught me... ;D

T

OD caps suck at RF and most Films suck at RF because of the way the lead is terminated to the film. It causes a high ESL, effective series inductance. The fact that it runs cool means nothing. You in effect have an RF choke in series with the cap which limits the RF current so the cap stays cool. There should be ceramic caps with short leads in parallel to reduce the reactance of the bypass.
This is very important at the VCC of the 414 drivers so there is plenty of stored energy when the device turns on.
All these little issues mean the difference between clean drive and crap drive.
Also between blowing FETs and not blowing FETs.

If you're using circuit board ...
Might as well use the surface mount version of the IXDD414's...
For even less lead length.

 :D


Tom what are those "chip caps"  ?

Not that I plan on building any class-e rigs... but just for reference.

AVX .1 uf 200volt Jay bought a bunch of them when we were building BB IRB boards last year.

I assume you adjusted the last pole on the PDM filter too accommodate the total capacitance.
I need to take 2 steps backwards now....oh well. It will be worth it in the end.
 

Yep, sure did.

More info:  I'm finally getting around to the fine tuning aspect of the rig... I wondered how much additional stray capacitance is really there generated by going thru the shutdown board, leads, fets, transformers near the chassis, etc. (in addition to the 0.3 uf X 4 = 1.2uf)   I used a cap checker and found a total of 1.2125 ufd. So there's about .0125 uf additional stray. That's not bad. So adding in the bypass caps and adding in the measured stray uf is a good estimate - then subtract the result from the last PDM filter cap value...

Actually, I did it the easy way - I disconnected the last coil and simply padded the last cap until the total measured was right on.


BTW, if you're really anal about it, be sure to include the damper diode which has about 1100 pf itself.

T

Brent,

Here's a couple of new tips:

I'm in the fine-tuning phase of the rig now.  I was trying to cure the last tiny bit of hum in the system. It was hard to find. It was so slight that nobody wud hear it on the air, but still bothered me in the mod monitor. I cured it by tying a large shield strap from the PDM generator board ground to the chasis. The small wires did not do it - it needed the wide strap. I also did some more bypassing and better wiring routing within the PDM chassis box. Now the generator is cleaner and there is no instability of any kind. The tiny hum it was generating is gone and now the quiet room ambience is louder than any hum.  I've never had a rig with such a low level of hum before.

Also added an audio delay - now keyup and unkey are totally quiet with no signs of spikes on the scope. I was getting tired of that darn HV relay  'CLACK!!'

T

Finally got around to listening to the audio file... Sounds teriffic,  Tom.  Well balanced audio with nice sparkle.  FB work OM !     Vic

And the C and L in the wiring harnes to the rf deck.
\
s

correction. OD and film caps are fine in high Z tube circuits where a couple ohms of reactance don't matter. A different issue when you are playing in the low Z sand box.

I'm back from a road trip to Texas..what a drive Phew! :o Was different when I was getting paid to do it. Anyway, I will be putting in an effort to finish this project over the next couple of weeks. Looks like I'm a bachelor for a couple of months ;)

Guys:

One thing I do that makes T/R smoother is I ramp the PDM generator chip up from no output to normal output by using a capacitor on the UCC25701 disable pin. My transmitter comes smoothly up in about 1/4 second.

As I am running the old 6 FET model without a driver chip, I also avoid a T/R relay. Lastly I keep the HV on all the time. All this results in smooth T/R with about 10db loss in received RF to my FT1000...and a simple system as I am lazy.

Dan

A follow up on fine tuning Rico:

I got new reports of a spike on key up and some hum.

The hum was cured by the PDM generator feed forward circuit - it's amazing how well it worked! I was able to zero out all my hum to a totally flat carrier.  The small hum remaining from the audio will hopefully go away when I get the balanced audio cables set up.  Evidently it was HV pwr supply hum. I'm surprised others get away with their supplies using the same amount of filter C without needing the feed forward option on their E-rigs - while I had a bit of hum without it..  

I think I licked the key up pulse problem too. The VFO enable was coming on too late (#2) and amplitude goosing the finals on key up. I moved the VFO onto the #1 sequencer position and the spike went away.  I cud see it happening at the vfo driver output when the HV was on.  I still have a double carrier key up, but the first carrier is down about 30db and is simply the 414 RF drivers bleeding thru at about a watt or so.  I tried moving the ant relay delay to later position (#3) - to try to block the first carrier, but then the finals ran out of time to dump their RF during unkey. I could see the fuzziness at about 1/2 way thru unkey. With a longer ant relay hold, the scope picture looks clean on unkey.

I listened to the VFO and I hear it move barely 3-4 hz when I modulate it with a big tone. Hopefully if it still has problems we can ID it on the air with some more help from the guys.  

This fine tuning is very time consuming. We're almost there and Rico Suave will be rolled into the corner as an official rig.

Many thanks to all the guys who helped identify the various problems on the air. Sometimes this is the only way to identify the finer issues. The clues are invaluable to finding the problems.


Dan - Tnx for the suggestion. I did try the cap but it didn't help my particular spike problem. It later turned out to be the VFO keyup, so it was unrelated....

T

Well, Tom you certainly sound better than I've ever heard you on the air in the past - and that's saying something, because you usually sound quite good !!

I have documented construction of a 24 MOSFET RF amplifier (and schematics) on the class E web site including step-by-step pictures of each stage of construction at:

http://www.classeradio.com/24_fet.htm (http://www.classeradio.com/24_fet.htm)

for anyone who wants to check it out.

Tnx, OM.  Hey, except for a few "JJ mods" it's all your basic design. It was a long haul, but well worth it. This transmitter is a cut above any modulation transformer rig I have. There's no way to get this super fidelity, power and low heat when using tubes. Setting up the audio for this rig has caused me to rebuild my audio system and make big improvements. The audio chain now uses balanced cables, has less hum, is more low-end capable and has cleaner highs. The e-rig demanded this due to no blower noise masking the low level crud and cleaner response. Rico will make a great summertime complement to the harem though I will still be running Fabio at times…(4X1 rig)

Of course I would not have been able to pull this off without your trailblazing work offering a fully functioning system design – and even supplying the boards. That helped things immensely. Even standing on those shoulders, it still takes some time and creativity to implement it effectively. I’m sure the e-rigs will continue to evolve and become even better over time.  Thanks for the help, Steve.  

Also thanks to Frank/GFZ, Jay/VD, Mark/ QFZ and others for advice from time to time.

Brent -  You said you needed a sequencer and shutdown board interface control schematic. I have not seen anything out there and don’t even have one for my own rig yet. I plan to draw out what I have here over the next few days and post it. Mine uses a 4-step sequencer with five additional relays slaved to it to handle all e-rig related functions. I hesitated to make a schematic since the rig was still evolving and even had some sequencer changes yesterday to fix the pulse problem. But we’ll get ya fixed up soon, OM.

Later-

T

I finalized my sequencing and control ciruitry, so wanted to post this schematic for Brent and future builders. I've not seen one out there yet, so maybe someone can draw this one out on the computer and put it into the E-rig site.

I did it from memory cuz the wiring harness is hard to trace in the rig at this point. But it shud be pretty close.

T

*Update - I see one minor error. The HV relay that gets controlled by three series of relay contacts should have an external +12V included in the circuit or whatever it takes to key the external relay which in turn keys the main HV relay.

Thanks Tom. I solved some of the problems from previous post by keying my sequencer off the VFO RY1 relay. Also series the B+ through the overload board. Will let you know when mine will be on the air....few more days to go.

Yuuuuuz guyzzzs missed it? Look closely at my layout and see whats wrong with waldo?! My dyslexia got me again. Had to tear down and redo the rf deck.

The winner gets a membership to the Macaroni net! :o ;D

Hey Brent, that's pretty good.....

You hooked the drains of the MOSFETs up to the RF drivers.....  :P

Anyway, those things happen...... but with proper pre-flight testing, nothing will be lost except the time it will take to correctly wire the devices  :D   But you know all about that sort of testing anyway  ;)

I have built a LOT of transmitters over the past 40 years, and I can tell you I make mistakes all the time.  But, there is never a component failure because everything is brought up on variacs first.  I even bring up low voltage and low power stuff that way - saves damaging chips put in backwards (which happens) and stuff like that!

Anyway, won't be too bad to move the gate leads to the driver outputs.  All in a day's "fun"  ;D

Regards,

Steve

Oh yeah, blame the dyslexia  8)  It's really that Hawaiian disease Lack-a-nooky starting to set in.  Turns the best brains to complete mush (Brent's wife is away for an extended family visit -and, well, Brent *is* French after all!!!!)..

Well that explains the problem I ran into :-\ Thanks for the parts yesterday.
I have 3/4 completed the rebuild and will start on the efficiency board later. Sometimes you have to take 2 step backwards to make progress ::)

P.s. your Macaroni membership card is in the mail ;D

I will have to fly back to TX for a conjugal visit :D

Sounds like you're making progress, Brent. Yes, your method of wiring the sequencer is FB - there's many ways to get the same results.


Yep, we all make wiring mistakes. I have some legendary ones that almost put me to the edge of tearing down the project.

I seem to do the worse damage during final testing and modifications. Adding to the other meltdowns, three days ago I accidently touched the +12V against the VFO driver board freq counter output. It blew out two chips that I had to reorder from Mouser.  Just got it fixed last night.

Here's a good test:  Last night I put the e-rig on at full carrier into the dummy load. I then used a fiberglass rod and banged around in the RF deck looking for bad connections. Wouldn't you know it - TWO of the chip bypass caps on the drains came loose!   They had plagued me for weeks as jumping final currents and slight noise in the AM monitor.   I had not used enuff heat on the bus. I resoldered them all and the rig is now rock solid. Clean and stable even with hard banging... ;D

I'm working on adding pretty blue LEDs to illuminate the meters. Also installed a temperature sensor that controls a digital programable kiln module to trigger the cooling fans at 95F or higher.  Most of the time the fans are off.

Also added full balanced audio cables throughout the audio chain. With the feed forward hum working and the new audio, I can't hear a trace of hum - but we'll see about the VFO phase hum when I get it on the air.  Almost ready for some new tests.

Brent, when wiring the FETs, remember the MOSFET pin-out as GDS -  Gate-Drain-Source   - "Gawd Damned Slopbuckets!"

T


** Look for some final pics of Rico Suave rolled into the corner soon. (All analog meters, digital meters, freq counter, temp sensor working and showing full strap parameters)

I noticed it Brent but I didn't want the Macaroni Net Card!
Enjoy it Steve ;D

HA! I just finished the rebuild....it was worth it. I paralleled up some .047's to make the bypasses for the input to the transformers and solder the source legs closer to the fets on the bus. I found the mistake in the fets cause of another mistake. I put the feedback diode in the filter output backwards :o So in conclusions 2 mistakes make a fix ::) HA!
Now onto building the new efficiency board.
I'll send you an honorable mention card Buddly :P

Don't bother. I'll just take the cash equivalent!

To maintain continuity to this thread, here's the posting of Rico's final pictures:

http://amfone.net/Amforum/index.php/topic,24276.msg179668.html#msg179668

Hasta la vista, baby!

T

A couple of folks have asked about the 0.1 uF chip caps used for bypassing...

Vishay/Vitramon VJ1825Y104KXEAT (Digi Key part # 720-1132-1)

CAP CER .1UF 10% 500V X7R 1825

Frank and I have been using these caps in MRI MRF150 amplifiers for coupling and bypass and I've been using them in the Current Mode Class D transmitters for output coupling and bypassing of the IXDD414 drivers. So far they've proven to be quite robust.   

I have done extensive lightning testing using these parts and they take a beating. There is an interesting effect with XR7 dielectric though. Pulse transients can reduce the effective C to almost 1/2 value during the pulse but the cap recovers.

Yes, those chip caps appear to work quite well. I use three 0.1's in parallel (0.3uf) for each module's modulated B+ transformer bypass point. So far they remain cold and FB during operation.

These chip caps can be soldered directly to a PC board creating zero lead length. The perfect choice for the job.


It's not a well focused picture, but see the PC copper board with a gap cut with a Dremel tool. The caps are soldered over the gap. The grounded end is aluminum angle that is bolted to the chassis. Keep the transformer leads short and you'll have minimal stray inductance.   The short transformer connections are on the back of the PC board - not visible, but short. The long red leads are B+ and can be any random length. The RF path is thru the short leads from the transformer, (in back)  thru the wide copper path, thru the caps and to gnd thru the aluminum angle.

Tnx for the cap suggestion Jay.

T

Tom, Where do you have those transorbs connected in the driver circuit?

Frank,

I don't use transorbs in the driver circuit.  I once added them at the input to the RF deck 414 drivers (at the junction of the four cable split), but found they rounded out the edges of the driver pulse due to capacitance.  I didn't try them at the final fet gates to see if it was any better.

I figure that the digital drive circuit with a self-contained VFO is pretty idiot proof, so no ricebox overdriven accidents will happen anyway.  There are transorbs in all the other obvious places, though.

T

Put them in the driver VCC line. Internal IXDD414 substrate diodes clamp transients to VCC on positive and 1 diode drop below ground on the negative side. Digital drive you take advantage or internal part die protection designed in and you won't load the output signal. As I said before any FET failure and drain voltage appears on the driver VCC line. This will cascade and take out all drivers and FET gates. This is why I thought each driver chip vcc should have a series diode. Feeling lucky......sucker.
This is why I run squarewave drive on the 160 meter rig transformer coupled.

Yes, we had talked about this before.

I already have an 18V transorb across EACH 414 VCC bus module to heatsink ground. (four transorbs as per Steve's schematic)

T

Good, but any FET failure will conduct back through the 414 substrate to the transorbs. Wanna bet who wins if the power supply gets across the 414 VCC bus. If you are very lucky the vcc bond wire will fuse in 1 414. Worse case everything blows. So a buck worth of diodes or load one round in the magazine and giver her a spin.

So what diode ratings and where exactly would you put them... in series with the VCC  to each 414  +lead? One for EACH 414 = 12 diodes?

T

 Nice clean project.
 BTW  thanks for the comments on the signal from my power SDR Flex 3000
 I still need to do perform more tweaking on the EQ
 Thanks again to you and the group on 75 AM.
  73's
KB2RSK

Tom,
You want at least 200 volts PIV for a diode. Yes one in series with each 414 power lead. Transorb and bypass caps right at the 414. This way if a FET blows and puts HV on the driver output the diode will be reverse biased isolating the HV from the driver power bus. I bet 1N4007s would work fine, 3 amp diodes would be over kill but fine. This way if something goes wrong you take out 1 FET, 1 driver.
My 160 meter rig with transformer coupled square wave drive, when a FET blows, yes I'm blown 3 or 4 since '95 doing stupid things the CT of the driver transformer shorts the DC to ground. Most times the FET just explodes and the rig keeps on transmitting. This is due to the current mode feedback modulator. Imagine replacing all the drivers and FETs after ascrew up....That would send you back to tubes.

Frank,

Each vcc bus feeds three 414 drivers which in turn feeds six fets.  Can I use one diode per bus instead? (four diodes total for all twelve 414 drivers)   Or will this cause six fets and three drivers to blow if there is a failure?

T

I put a transzorb across the VCC for the each group of IXDD414s.  A series diode in series, at least with each group of IXDD414s +VCC line is not a bad idea at all - or if you're really paranoid, a diode in series with each IXDD414's supply.

I'm guessing you have transzorbs across the drain busses as well.  You have an overload shutdown that kills the main power supply along with the pulse train.

There is nothing at all wrong with "belts and suspenders"  :D

One thing that has really come far over the past few years is protection.  The old days of the catatrophic failures are behind us. Think about it - there would have to be a lot of things failed, and all at the same time, to get any sort of cascading situation going - and even then, you've taken steps (as outlined above and in posts by Frank and others) to stop it.   If something shorts out in the RF deck.  The overload shutdown immediately kills the DC to the RF amplifier before the real current gets going.  The instant the current rises faster than the voltage, the overload detect stops everything cold.

Those 18V transzorbs are amazing!  Bob K1KBW, using analog drive, had his driver putting out some 80 watts or so into an 8 MOSFET transmitter.  After a little while of this, the transzorbs finally gave up the ghost and shorted dead, but the gates were unscathed.  I've never had anything get through them under any circumstances..... but there's always a first time...

I use seperate power supplies for each module's IXDD414s in my designs, with 18V transzorbs on each power bus.

Never had a failure of any kind whatsoever the RF amplifier, modulator or driver despite my best efforts to transmit at full power into no load (many times), or on the wrong band or into a dead short or with no drive....  The only thing I've had to replace were 2 50 ampere bridge rectifiers in the power supply... and this was due to an open step-start resistor.  I put in a "real" resistor, and no more rectifier problems!!

Thanks for the suggestions.  I'll add some diodes to the 414 busses the next time the RF deck is pulled out.

T

I've done a lot of lightning testing of transorbs. We hit 3 series 15KW transorbs with 1/2 million watts of WF5A pulse with the diodes at 85 degrees C and they hung in. I hit them 10 times with no effect.
OTOH they have a low steady state dissipation rating (few watts). Shorting the drain to the gate of a FET will place the DC supply on the transorb through the substrate of the driver. I bet the shutdown circuit isn't fast enough. I bet you have less then 500ns time to get it disconnected. Since this is a short you have to stop the pulse train in the modulator and discharge the filter.
Let's see a couple bucks worth of diodes or hope this never happens. Your rig...

On 75 last night I suggested a quicker shut down possible if the drive signal could be forced to zero on both phases. Jay suggested this could be done with the enable of the IXDD414. So the simple addition of one IXDD414 controlled by Steve's overload board could be used to control the enable of all the driver chips for a quicker shut down. Killing the PDM still leaves the caps in the filter charged so there is still energy to dissipate if the drive is still running.

So then...as discussed...the 414 enable pins should have individual pull down resistors to ground and individual series diodes to the 'enable bus' just in case HV blasts through the FET and IXDD414?

Wish BP had disaster planning ...

Well, if you really want a nuke cert you need to do the same thing on the inputs of the 414s. I would put a cap 100 pf to 1000pf  across each input  diode.

An update. I rewired the SU-5 transformer thanks to Jay W1VD and got a quiet transformer. After I did the 20 amp brick rectifier took umbrage and shorted. Replaced with a 50 amp brick; now that the power supply was delivering its full current the step-start resistor opened up and I kept tripping the breaker. Replaced with a 10 ohm wire wound and problem solved. The transmitter was current starved and the audio actually cleaned up.

Brent W1IA