The AM Forum

Hello all,
Started the gathering of parts for the 75meter 1KW class E transmitter Model "DJS-1000-75E" :)
I have been talking with Steve some and looking at schematics and for the first one I think much of what I will use are predesigned boards.
Therefor much of this discussion in the beginning will be about gathering of parts, fabrication, layout, etc.....
I know there are many of you that have already build these types of units so any helpful techniques to avoid issues down the road are welcome
As I build the transmitter and post pictures and comments, I am sure conversations will go in many directions, but the plan is to take the entire journey on this thread of AMFONE.

tks
KK6IRZ/KA1WLZ

Started figuring out the VFO. Somewhat the VFO shown on classicradio.com but already know I will make some changes for keying and spot but generally speaking it will be close.
Have the Supply A and Supply B done.
Found four 27000uf 160V caps in my junk drawer and a Hammond HPS 2000VA Transformer, FET one the way, bla bla etc... so the gathering is one the way.

Hi All
I am building the phase splitter driver this weekend so if anyone has and rules of thumb or point of addressment I would love to hear it. I have attached my board design although just showing the top side. does not seem like anything to magical but I am sure I will get a surprise when I run it. :)
Look forward to hearing any helpful hints.

Thanks
Jeff
KK6IRZ/KA1WLZ

Hi Jeff...

This is going to be an interesting and very big build...
Many FETs and drivers etc: and testing along the way  ;D

I do listen at times to you guys on N1NTE and from memory where is only 2 stations running these TXs at that power level .... Steve and Brent ( who only operates during the winter months ) ...
Bob K1KBW runs 400 Watts and his signals are very strong most of the time....
He also has a WEB site with photos that maybe worth while looking at for ideas etc:

Have you build these circuits before ?
What is the VFO ?
There is also a duty cycle circuit ( on Steves WEB site ) that probably would be best to makeup...
If it was my TX would prefer both those circuits on the one board...instead of them all joined with jumper wires etc....

That will do for the moment...


Wayne

Hi Wayne
Yes it is going to be a fun build but I have many of the parts already in boxes and bins. I am of course getting much information from classeradio website but I remembe4r the days back in the late 90s early 2000 when this was the main building conversations on the East coast. I have always been dominantly a Tube guy and when I say dominantly I mean I have one solid state rig and a Garage full of tube gear.

I have seen Bob's stuff and looks like some nice builds although I think recently I saw him playing with a 24 FET version. I think in that version he used some Doug's output boards which I also plan on using for this build.

I have build many transmitters over the years from 10 watts to 100,000 watts. Mainly between 1992 and 2005. Have not build one of these rigs so it does provide a little new for me but have had many other products over the years with similar technologies just not always RF.

I have not decided yet on the VFO specifically, have though about a DDS but being this will only be for 80 meters I was thinking I may just build a Colpitts oscillator to operate 17 to 20Mhz and then slice it down to 3.5 to 4Mhz for operation. Or I could just stick a china generator into it HIHI.

The photo on my last reply actually is based on Steve's VFO schematic on the website. on that prototype board I will be using junk drawer parts so the pots are actually not shown on the board but there is a trace that a panel mount pot will tie to. :). This first board is just a prototype to get things started which would be the standard frequency cut in 1/2. I am just doing it to get some visuals on the waveforms. Later I will design and build a board with protection and whatever PTT controls I may decide to use.

I do appreciate your comments and advice on keeping things tight and complete on the board. I am looking forward to a fun weekend of playing. I may even build the power supply this weekend if I get motivated. I was lucky to find all I needed already in my horder stockroom hihi.

See Ya 73

Jeff

OK EVERYONE I JUST REALIZED I WAS SIGNED IN AS KA1WLZ WHICH IS MY OLD CALLSIGN

Dummy me.
Hi this is still Jeff but with my current call.

:) :)

Hi all

Thanks to Doug for sending me a set of his PA FET Boards they look great but there are 2 parts that are currently not available anywhere that I have checked. Maybe one of you have some spares.

Need 4 BUT WOULD LIKE TO GET 8 of the 100C152KT500X and Need 4 of the 900C224MT200X
I have everything to build the 24 FET PA except those 12 parts

CQ CQ CQ who's got the stash?
:)
 

The boards are beautiful snd compact. Downside is that they use some expensive, hard to get caps in a few places…

For the 1500pF caps, look at these MLC Micas made by CDE.
They are rated at about 10 Amps at 1.8mHz and higher at 80 meters, so their ratings are very similar to the ATC100C caps.

https://www.mouser.com/ProductDetail/Cornell-Dubilier-CDE/MC22FF152J-TF?qs=aUB389kaodB6G%2F9MgOGeXw%3D%3D

I am going to use 3-470pF ATC 100E chips in parallel I bought a few years ago.
The values are not exact as long as they are big enough to prevent a spike that would kill the 11C90s on each bus. Nominally, 250pF per device according to Steve

The 0.22uF chip capacitor looks tougher to find.
I wonder if a WIMA low ESR film cap might be bootstrapped in until you are able to order the 900C chips…

73, Mike K9MB

Hey Mike
Thanks for the info and yes there are choices for other parts that would do the job but being Doug made such a nice looking board I was hoping to stay with the designed parts. hihi we will see.
I am actually a fair part into the experimentation of lower lever items.
Built a FET Colpiitts oscillator with a range from 7 to 8 Meg very stable even spread-out on the bench so when it is finalized within an enclosure I expect it will be more than adequate divided down to 80 meters.
My phase driver is also on the bench and working and I have good smooth control of the duty cycle and have everything for the PA except this parts.

I am hoping to hear fromn Steve sometime with hopefully new on availability on the boards and parts he has but it is the holiday season so I would imagine he is busy with more important things that putting together board kits hihi LOL
Anyway thanks for the suggestions and I will check it out but for right now I will keep searching for the design originals :)

73s
Jeff
KK6IRZ \ KA1WLZ

Ok Guys found a stock pile for $5 each on the 100C152KT500 AND $6.30 ON THE 900C224MT200

Thanks to those who looked and thanks for the comment

It would be interesting to know the source you located for these capacitors.  Could you please provide a link or other information for those who are also building Class-E transmitters?  Thank you!

ah sorry
I use findchips.com
they monitor many different distributors but in this case I got them from Quest Components.
I think I got the last of what they had but maybe someone else will pop up.
When I first did the post there were none available so I just loaded the part numbers in the notification area of my account and when they came available I went and grabbed them.

With all that said, findchips 99% will get me what I need

thanks
Jeff

Little added information on parts used with the PA.
I will post the list as it gets bigger but for now here is what I got

Thanks
Jeff

Hello All
I am using the Boards that Duog N9SHU provides
Anyone know why there are an X1 and X2 position for mounting SMA connectors.
I have not ohm everything out but they seem to be connected together and was just curious to why there is not only one location for the input to the board.
I asked Duog but have not heard back from him so thought I would see if anyone had some insight.

Thanks
Jeff

I understand that the second sma jack footprint is unused for the 24 FET rig, because each 12 FET board is the same phase, but there is an option that I am taking- to make a one board 12FET rig. That requires some cut traces and jumpers and Doug can provide that mod, if anyone wants to do a 500-600 watt 12 FET rig.
If you are doing 24 FETs, ignore the second SMA footprint.

Thank you
I figured it was for a mod for a one board PA but could see that it would require cutting and jumpers so I thought maybe there was another reason.

No worries, I am doing the 24 FET using 2 boards so should be no changes needed.

Thanks for the verification.

I am 3d printing a Ferrite Bead holder for my transformer configuration and should have everything mounted to the Heatsink next week I hope.

I am debating on heatsink compound or pads, Pads would be easier but compound works better. With the expected high efficiency it probably does not matter much anyway. :)

Again Thanks

Jeff

Would like to see your Ferrite bead holder.
You will need to be sure that the Ferrite has good air circulation so heat can be dissipated. It is not a lot of heat, but even a small amount can cause cores to get hot if they cannot dissipate the heat.
I just glued the cores together in stacks and put copper tubes through them and then wound the secondaries through. If you use circuit board to connect the copper tubes and cut gaps, you can use the fiberglass FR4 to provide support and terminals can be attached to standoffs to make it all rigid. Lots of ways to do it.

OKIEDOKIE
Little explanation

First this transmitter is being built in a 21.5"Widex14"Highx15"Deep cabinet. The idea being that this would be like a old boat anchor transmitter sitting on a desk but able to do 1kw.

The heat sink is mounted on the back of the cabinet at floor level with the 2 PA boards mounter horizontal with the transformer between the the 2 boards but actually mounted to the floor of the cabinet.

The ferrite bead support has a .75 hole on one side to keep the beads from sliding out, a support that aligns to the middle of each bead to hold things straight, and then a cap which gets put on the other end of the support to lock all the beads into place. (Cap Not Shown)

Here is what it looks like

Thanks
Jeff

Thanks for the explanation. Nice design on the core holder. Plenty of airflow there, I am sure.
I would love to see it implemented when you get it going.
73, Mike

No Prob Mike

I will be starting the initial physical layout in the cabinet in the next couple weeks.
I had several of the holders and end caps printed but waiting for them to show up.

I have most of the design worked out in my head and have been doing solidworks models of all the parts so I can work out mounting and final layout details in a virtual world before actually drilling and blasting.
Although I do have just about all my holes drilled and blasted on the heat sink at this point. Maybe by the end of the weekend I can at least post a picture of the heatsink and PA boards all mounted in the cabinet.

Hihi we will see

thanks
Jeff

Just to provide a little closer representation of the Ferrite Bead holder.
Here is a image with beads and wires
Just to make it easier to see how it will look

Thanks
Jeff

This is going to be a great build !!!

There are 6 of the 24 MOSFET transmitters on the air that I am definitely sure of.   I think there is one other out there, but I can't remember who has it off hand.

The bypass capacitors at the DC side of the RF output transformers have been an issue with the boards in some builds.  This is a high current point, and we have seen some capacitor failures in the field.  Whatever capacitor is used as the DC bypass capacitor *MUST* be a high current capacitor, at least 7 amps and preferably 10 amps ( at the real operating frequency).  The problem gets worse the lower in frequency you go.  So, it's worse on 160 meters than on 75 meters.

The other thing if note is that the ideal value for the bypass capacitor is .15uF and not .22uF.  This was a change made in the field due to the fact that, at the time, the .15uF multilayer ceramic caps were not available.

This is a solvable problem!!!

Looking forward to following the progress of this build.

Regards,  Steve

Hi Steve
Thank you for the info
I am only doing 80 meters for this build

When I received the board from Doug he had a list of part numbers that he said were already qualified as being right for matching up with board design. The part number he gave me was the .22uf 900C224MT200X and I did notice that it was different than the schematic on the site.
However, I figured it was possibly due to board design adjustments.
I still do not see the .15uf caps available so I assume on 80meter I will do ok with the .22uf caps I have available.

Also Steve, maybe my emails are going to your junk folder.
I sent a couple request on getting your 3 board set with parts

Anyway, I expect to be running the board through the reflow oven next week for all the surface mount parts and then will install the through hole parts. Still drilling and tapping the 5 billion holes in the heatsink. hihi LOL

Again thank for the info and let me know when you can about the board sets and parts

Thanks
Jeff

Hi Jeff,
Thanks for posting the representative image of your core holder. It is exactly as I visualized it. Very nice design. 73, Mike

PS: If you decide to make some extras to sell, let me know. MB

One of the things we're looking at is to stack several MLC capacitors in parallel.  Possible 3 .047uF devices, or maybe a .068, a .047 and a .033 in parallel.  Still researching parts.

This is to increase the current handling capability of the RF bypass capacitors at the DC side of the RF output transformers.

Steve- Isn’t this cap in parallel with the PWM output LPF cap and form the total value of the output capacitance?
I am asking because I am planning to use WIMA high current, low inductance caps for the filter and it has never been clear to me whether the requirements for esr and rise time for these 0.15 uF caps has to be better in HF ESR than the WIMA puse caps.
In this case, you have two 0.15 UF caps in parallel across the PWM output LPF circuit, or 0.33uF total- right?

Please clarify the requirements for these caps- and whether high speed WIMA film caps can work well here. If so, it seems like straining at a gnat to try to stack these MLCC caps when bigger ones could be bootstrapped near the board. Please comment and also correct me in this matter. Thanks, Mike

Hi Steve and all else
Please keep in mind that I am only doing 80meters so I hope the .22uf will be ok.
However, if the idea is to increase current, keep overall capacity at .15uf, fit nicely on Doug's boards, and be available for purchase then maybe the C4532NP02E683J230 would do the trick.

the pads on the board are made for a chip 2525 and these are 1812.
I already checked the layout and it would fit nicely with 2 of those C4532NP02E683J230 parts side by side on the pads. That would be .136uf pretty close to the target .15uf and I have a bunch in stock and I can see they are also available for purchase at Mouser.

What are everyone's thoughts on that possibility?

Thanks
Jeff

Jeff -

The cap you are talking about does indeed become a part of the last stage in the LPF filter.  But it's effect is minimal as far as the filter characteristics are concerned.  Small variations in its value will have essentially no effect.  As Steve has pointed out, it's main purpose is to provide RF suppression at its point in the circuit.  As such, it's important to have a low ESR rating.  Distributing its capacitance between different caps is a plus since that divides the current surges.

Rod KQ6F

so very interesting
So it sound like the .068 doubled up would meet the intended of .15uf value before the .22uf cap was used due to non-availability of the .15uf.

I have about 100 of the C4532NP02E683J230 and may try two of them in parallel

tks
jeff

Hi Mike,

Any good cap can be used in the PWM filter.  We have not seen any issues in the field with various capacitors in this part of the circuit.

The reason that we can't put a lot of extra capacitance at the board is that the overload shutdown circuit, which is fairly fast and is located after the PWM filter, will start reacting to high audio frequencies from the modulator being fed to too much capacitance at the RF amplifier.  This will cause false overload triggers at high audio frequencies which is not desirable.

It was kind of a balancing act between getting sufficient bypass capacitance to do the job, without putting too much capacitance there where false overload triggers would be an issue.

Regards,  Steve

Thank you for the explanation, Steve. It makes sense. I knew that you have used Orange drop caps there in the past, so the WIMA caps I have would be even faster than the orange drops, so it should work.
Interesting that the rise time spec is so fast that the bulk of the output filter capacitance is not “visible” in this time frame. Anybody who has done anything in RF or high speed buses knows that a trace to a “ground” or low impedance- looks like anything but. 😉

Just about the time I think I have peeled this onion to the middle, I learn that I know nothing much about it. It is great to have you as a resource.

quoted by steve_qix 1/5/22
Hi Mike,

Any good cap can be used in the PWM filter.  We have not seen any issues in the field with various capacitors in this part of the circuit.

The reason that we can't put a lot of extra capacitance at the board is that the overload shutdown circuit, which is fairly fast and is located after the PWM filter, will start reacting to high audio frequencies from the modulator being fed to too much capacitance at the RF amplifier.  This will cause false overload triggers at high audio frequencies which is not desirable.

It was kind of a balancing act between getting sufficient bypass capacitance to do the job, without putting too much capacitance there where false overload triggers would be an issue

Thanks for the info Steve
So the 2 caps I suggested again sound like a good choice to try.
With two .068uf in parallel the total capacity of .136uf is still higher than the low side tolerance of the .15uf original caps.
I may need to cherry pick a bit to ensure the .068uf caps are on the equal to high side of tolerance but seems like it is possible to be a good choice.

I am curious Steve if the issues that were seen connected to false overload trips could be related to operators trying to modulate beyond 100% and using the higher .22uf caps?
Also Steve were this seen issues while operating on 160 or 80 meter?

Thanks
Jeff

I do not think there would be a difference between 160 and 80 meters for the bypass capacitors.
I suppose that if the Xc was marginally high, it would, but that should not be a factor in a choice between 0.15uF and 0.22uF.
Of course, the shunts on the drain bus are much more important to limit spikes that can toast the 11N90s. Those are indeed and specific and also bus length specific, in terms of number of devices.

For the overload shutdown circuit, high rise times are essential, so the larger value slows it down too much and affects function of the shutdown circuit.

To answer Jeff's question - we actually haven't seen many false overload shutdown triggers at all.  Usually if the overload (properly adjusted,  of course) triggers, there is a real reason for it.

The way the overload shutdown works is with a window comparator.   The current is constantly compared to the voltage, even as the voltage moves around.  So, if the transmitter is modulating very high in the positive direction, the voltage is higher and therefore the allowable current is higher - because the current is compared to the voltage. 

This differs from essentially every other overload shutdown scheme I've seen, where typically only the current is sensed, and since the current varies with modulation, false triggers are highly likely if the overload shutdown is to actually be able to protect the transmitter in any real sense.

Hey Steve sounds good
So it sound like the theory is if to much capacity is used at the bypass it has higher possibility of a false trigger but reality on the transmitters out there is that if everything is adjusted correctly there is little cause for alarm for possible false triggers using .15 or the .22uf caps,

The real issue in the field is the current spikes on the bypass caps and parallel caps would provide added capability in that area of the circuit.

With all this information I think I will try the .068uf in parallel
It will double the current capability and still keep the value close to original design.

thanks all
Jeff

Hi guys sorry it has been awhile. I have been finishing off a homebrew Tube rig, pair of 8005s modulated by a pair of 811s.
I was playing with the digital phase splitter driver and has a couple curiosities.
Being that I am using the PA boards from Doug should I really include a phase adjustment on the driver? I of course have control of duty cycle and it seems to be working fairly smooth although I did notice I may need something to indicate that both are exactly the same of does some variance cause little issues?
I would be interested in your thoughts on this section of the transmitter

Thanks

KK6IRZ/KA1WLZ

Hi Jeff

As far as the Duty Cycle goes I would adjust it as best you can using your CRO as an indicator....
Its hard to get them exactly the same as the waveforms will be slightly different....
Doing the best you can .. to get close enough.. is good enough I would say....
I don't think an indicator would be of benefit really just use your CRO etc:

If the two phases from your Flip Flop are 180 degrees apart that should translate to the gates...
By using your CRO monitoring both phases at the gates you could simply move them together and check the phases are 180 degrees apart....

Does this answer your questions ?

I'm sure Steve will reply ....


Wayne

The goal when adjusting the duty cycle is to maximize efficiency, with the side effects of higher output and lower harmonics. A couple things need to be understood…  efficiency and power both come when both banks equally share the load and together, they’re on all the time (each half the time).  This isn’t at a straight 50% drive on time…or this would be easier.  The gates are capacitive.  They take a certain time to charge and turn on, and another amount of time to discharge and turn off.  The point of drivers like ixxd614’s is to pass big currents quickly to turn them on faster…the duty cycle being a bit below 50% is giving one side time to discharge and turn off before the other side turns on. In other words the mosfet essentially stretches the drive pulse, its output is on longer than its input.

So when adjusting duty cycle, you want to measure efficiency and watch power levels, too.  Power in (DC) vs power out.  If the duty cycle is too high, there will be overlap, and a lot of heat. If too low, power will drop.  Efficiency MAY peak when there’s a little under lap, but the power will drop a little.  Some people will say how great this is it’s so tweaked and so efficient….but it also has more distortion/harmonic output. Target highest efficiency then rock to each side for max power, which may or may not require any change at all. It may also be instructive to us the add function on your scope with the two drain currents…if there’s gap or overlap, you’ll see more variation.  I suggest you play with this at reduced power…where you can deliberately misadjust it to see what happens without risk of blowing it up.

Ed

Ed, I don't think anyone could have said it better !!!!!

That is it exactly.  The drivers and the MOSFETs all add a little to the "on" time of the waveform.  So, you have to use a duty cycle (as measured at the gates of the MOSFETs) of less than 50% - usually 40% works very well.

OKIEDOKIE!!
I have the duty cycle under control and can smoothly adjust it for both wave forms out of the Flip Flops. The cable going from my driver box over to Doug's boards are exactly the same length and I am not seeing any added phase shift at the inputs of the boards.
Looks like I will not need to worry about variations in phase so I only am using duty cycle control with no phase control.
So Far so good. Now I just need to get the PWM boards from Steve so I can finish my layout.
I am sure I will have more questions but so far things seem to not be giving me much of a hard time.

Thanks
For All The Input.

Jeff

Hello all and Hello Steve QIX

Steve I have been sending emails hoping to get your boards and parts for this project.
I hope you are ok because I have not received a response in some time now.

I am hoping you might see this post.

Are your PWM 3 board set still available?

Thanks
Jeff
KA1WLZ/KK6IRZ

I am not sure what PWM version you want, but I have some REV C boards. They require a few mods to get them equivalent to REV F. If Steve has some REV F boards, it is more convenient, but REV C boards will work fine with Mods, Steve has told me in the past. I was able to get a set of REV. F boards to save making mods.
If you are interested in the REV Cs, I can make sure I have them.
73, Mike

Hi Mike
Well I will hold a bit longer to see if we hear from Steve but if not yes I would be interested. I was hoping to get the 3 boards and parts combo package from Steve but if not I can still make it work.

Thanks
Jeff

I agree, Jeff. I got the C boards as kits and then got sidetracked by life and when I got going again, the versions had passed through C,D, to F.
They are essentially the same boards with new mods that can be added to tue Cs, but the Fs made it cleaner.
I Used kit parts plus added more to get my boards stuffed.
I have some extra parts like the current sensors ICs, BPT, FETs, and other things if you cannot get complete kits. I Always buy extras to lose and some to destroy- you know. 😬😉
73, Mike

I am missing some key parts for the PWM boards :-(   When I moved from Townsend to New Hampshire, somehow I lost all of the LTS 25 NP Hall Effect devices !!!  This represents a couple-thousand dollars worth of parts.  I know I have them somewhere.  These aren't available anymore.

Let me know if anyone can find some of these parts - the system won't work without it.

Steve, isn't there a drop-in replacement from LEM?  CAS 25-NP
https://www.lem.com/sites/default/files/marketing/lem%20leaflet%20cas%20casr%20cksr.pdf (https://www.lem.com/sites/default/files/marketing/lem%20leaflet%20cas%20casr%20cksr.pdf)

IF (yes, big IF) they work, Digikey has a couple hundred in stock at $17.07/single piece

Ed

I bought 4 of these last year.

https://www.ebay.com/itm/322226781590

They are only $5.22 each.
If you need a couple, I can send them along. I found one in a kit I got from you and put that one in my overload shutdown board, so I just kept these for spares.
It took about 6 weeks to get here from China.
I can send a couple for you to test before you order any of them to make sure they work correctly.
 No payment- Just give me a credit or replace them when you find that big hoard under something you forgot about- been there…😉
I can send out right away. 73, Mike

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