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811 bias for Mod




 
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w9jsw
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« Reply #75 on: January 05, 2019, 09:10:54 PM »

Back to the tank coil. My thoughts were along the lines of the second pic. A single tapped coil with a shorting bandswitch. How do you calculate these large coils with various types of cu tubing? On the first one, what kind of bandswitch can switch in different coils? Where can I find out how coil stock affects inductance?

Update - did a lot of studying this morning, getting a handle on it.
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« Reply #76 on: January 06, 2019, 07:42:47 AM »

Tom,

Found a band switch - see PMs

John
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« Reply #77 on: January 06, 2019, 12:35:56 PM »

Back to the tank coil. My thoughts were along the lines of the second pic. A single tapped coil with a shorting bandswitch. How do you calculate these large coils with various types of cu tubing? On the first one, what kind of bandswitch can switch in different coils? Where can I find out how coil stock affects inductance?
Found a band switch - see PMs
Update - did a lot of studying this morning, getting a handle on it.


Hi John,

To calculate the coils, go to an online coil calculator and pi-network calculators.   Between these two you will be able to enter a Q=12, and go from there.  

Enter the coil dimensions to come up with the number of turns per band.  You can short the coil for the various band taps from the loading capacitor 50 ohm point up the coil towards the plate tuning C1 cap. Put multiple coils in series with the smallest at the plate tuning cap end - with the bigger coils (160M) at the 50 ohm end. Know what I mean?

The type of coil stock will have a small effect on inductance. The coil diameter, turns per inch and coil length have the biggest effects.

The PM you sent with the various auction coils, bandswitches and other components are all in the ballpark to use for 813s  @ 3KV.  To save money, I would approach the guy with the picture showing the two white chimneys. Make a deal on the bandswitches, the plate choke, coils AND there is a metal turns counter sitting inside the chimney... See if you can buy the whole lot cheap.  Send him an email and once in a blue moon they will cancel the auction and do a special deal... :-)  Otherwise just win the auction and try to buy the other stuff too.

That strap/edgewound coil will be plenty for 160M and can be used on 75 and even 40M.  But for 40 M and 20M I would rather use one of the 1/4" tubing coils shown. They have better dimensions for the higher bands than the edge wound coil.

Coils like to be 1:1  to 2:1 length to diameter ratio for best Q.     IE, a coil that is 4" long and 3" diameter is in the ballpark. A coil 12" long and 3" diameter is NG.  Keep the coil turns spaced apart as "reasonably" wide as possible to keep inter-turn capacitance lowest.  However, wider turns spacing decreases the inductance. This may be good or bad when tailoring for the specific band.

I would clean all of that stuff up with solvents suited for the job and silver plate everything you can.  This is an example of how a dirty tank assembly can make a nice rig look like crap.

I was looking at the silver plating processes on the web and it's pretty easy. From what I briefly read, use a 12V battery with two chemicals in a big glass bowl and you're in business.  It's all on the web to read.  The chemicals can be purchased on the web.  

Can someone here chime in about their experiences /dangers with DIY silver plating ??


T
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« Reply #78 on: January 06, 2019, 01:25:57 PM »

Take care, the process uses potassium cyanide or silver cyanide,VERY, VERY toxic. Also, when the PH isn't correct one can produce cyanide gasses. So when you smell almonds when opening the jar with chemicals or during the process, leave running
There is a cyanide free process, but the maximum thickness is about 20 uM. For the 10 meter band ok, for the lower bands not sufficient, the skin effect goes deeper at lower frequencies than 20 uM.
There is also a method to put a silver layer at isolation materials like glass etc.
But when you leave the solution for more than a few hours, a high explosive silver nitrite will form. There were quite some accidents when people just left the solution and moved or just touched it after a while. Silver nitrite is a high explosive, please take care.
I had children in the house and gave the chemicals to a waste center where they could dispose of it with great care. I rather use a plating center where they have the knowledge.
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« Reply #79 on: January 06, 2019, 01:34:43 PM »

Thanks much for the info, Nico!  Scary stuff.

I guess if it were easy everyone would be doing it DIY- but they're not. I have a few friends who have had professionals do it for them in plating tanks. Chuck's rig is an example. Now I know why.

No DIY silver plating.

T
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« Reply #80 on: January 06, 2019, 01:42:08 PM »

I've used those open frame contractors on some very large 10 meter amps.

Tetrodes with handles, twin 3cx3000, etc.  If you really want them to be bulletproof and drop to almost 0 ohms in a 4 wire tester, put some (multiple layers) KOOL AMP on them....  Poor man's silver whetted contactor.  Been there, done it, works a treat.

Biggest issue I had with them at the upper bands is you have two sides to detune.  I was never able to get 0 reactance on them with a single bypass cap.  I ended up with a bypass cap on each arm.  Probably not an issue at 40 meters and lower.

HOWEVER!  They are slow, and if you use them only for output keying, you will probably end up hot switching your output.  The 12 volt ones should be run on 18 to 24 volts with an appropriate dropping relay to speed them up.  To speed up the release, you can add a resistor to the ubiquitous anti spike diode.  That will still damp the inductive kick,  but provide a quicker release.  (not my idea on the release.  Don't remember where I read it, probably some amplifier forum).

I have a couple of those Jennings dpdt relays around here.  Total cats meow.  Also, look at the break rating.  The top contacts would make a darn good overcurrent break relay.

--Shane
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« Reply #81 on: January 06, 2019, 06:04:03 PM »

Would you trust buying a Jennings RB3 on ebay? Will give me 1 week to test it. Good price.
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« Reply #82 on: January 06, 2019, 08:19:03 PM »

Would you trust buying a Jennings RB3 on ebay? Will give me 1 week to test it. Good price.


Sure. I buy stuff all the time off eBay.  It's a plus if he's a ham.  Google him and find out all about his activities and reputation and you can pretty well tell who you're dealing with.
Is it Steve, $85? He has 100% rating with 2K sales. Looks good.  

How would you test it in a week?  A hi-pot test could show bad vacuum as an open contacts fail.  But how about current test?  You could put some RF thru it at 50 ohms. Maybe Shane knows a good, easy way.

Just to be sure...  you could probably get away with the $25 open frame relay as Shane agreed... but I prefer the Jennings vacuum. It's real  overkill and like insurance.  Of course we must remember that a plate modulated rig  capable of 1KW carrier can generate 5 KW pep RF power, so it's really like a BIG linear.  I mean, WTF.

T
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« Reply #83 on: January 06, 2019, 09:49:22 PM »

I have been buying a lot of stuff lately so will hold on the vac relay.

Just got done with the 2 threads of Fabio II and taming the beast and the audio games. Am I in for some fun or what! Hopefully twin 813's at 2700V is not as much of a fireworks show.

Put a bid in on the tank stuff. He had the other stuff for a project and was selling the parts of a lot he bought to get those other parts.

Made my first order from Russia on some doorknobs. Also got a 3A variac for $25 bucks plus shipping. Still need a bigger one for 1/2 of the 240 feed.

Winterfest 2019 is end of the month here in STL land. A big show. Hope to score a vac variable for the plate load there. Perhaps an antenna load cap as well. Most of the other parts are coming together.

Starting to think about sequencing. Is that 4 relay board you started with a good way to go, or should I take the discrete approach. Recall that I plan to feed the rig with a DDS VFO driving a 20W IRF510 push-pull SS amp. Do I need to put a relay on the drive input to the big rig or can I just plan to cut power to the amp to stop the drive?

On the big relay for the antenna, why DPDT? I get that half of it is switching the antenna between the TX and the RX. What is the other half doing?

Should I be planning on some failsafe sensors like you did on Fabio II to cut off PTT if bad mojo happens?

Later,
John
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« Reply #84 on: January 06, 2019, 09:51:08 PM »

John,

Lest I forget...

The Jennings relay terminals are extremely fragile in regard to stress. I have broken one or two in my time as well as many other guys. Be careful when tightening the screws and support the terminal when doing so. A direct turn of the screw without support will usually crack the glass and bye-bye vacuum.  If you use strap, be sure it is pre-formed to align without stress.


The next frontier:

Since you are in the design phase, you will soon be designing your front panel layouts. If you want to take a quantum leap, study Chuck's front panel on his homebrew 4-400A AM rig. Notice the incredible balance and symmetry. Big lights, brass bezels, beautiful knobs, etc. Obviously he spent a lot of time figuring this out and getting the internal parts to mount correctly, etc.  This is like 3-D chess. Building a good layout for RF, making the panel's layout symmetrical and making it pleasing to the eye - is the mark of advanced work.  You might as well shoot for this kind of finished product. You will probably not get there on the first rig, but you will be far ahead in the end if you are aware of these things and make it a goal now.

As I've been told, "If it's worth doing, it's worth doing right."

** Over time I have found this is the difference between whether your rig eventually gets torn down for parts or someone begs to buy it for a few grand.  Over the years, I have noticed that Chuck always gets a good price for his rigs - the demand is there... all the way back to high school.  How much do you think his latest rig would bring... $15K? more?    Smiley

T  

 


* K1KW balance.jpg (101.22 KB, 600x800 - viewed 66 times.)
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« Reply #85 on: January 06, 2019, 09:59:12 PM »

Already been thinking about the panel layout.

Looks like I will not be getting a PCB from Rich. I see that he cancelled his license in 2018 around the same time of his last logon to this site. I was thinking he was SK, but found him alive and well on Linked In. Anyway, he has not responded to my email for over a week, so not holding much hope.

I may very well do the board myself. Looks pretty simple. I did a PWM driver on EasyEDA a few months ago. They are not very hard to do. I used to use Kicad but find EasyEDA easier - more straightforward. That is where I have been doing my schematics.

John
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« Reply #86 on: January 07, 2019, 07:45:59 AM »

Back to the tank coil. My thoughts were along the lines of the second pic. A single tapped coil with a shorting bandswitch. How do you calculate these large coils with various types of cu tubing? On the first one, what kind of bandswitch can switch in different coils? Where can I find out how coil stock affects inductance?

Update - did a lot of studying this morning, getting a handle on it.

If you can give the diameter of the tubing you plan on using and the projected plate voltage and current, I have a MatLaB program that calculates this stuff in 0.1 seconds.


Phil
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« Reply #87 on: January 07, 2019, 12:51:52 PM »

On the big relay for the antenna, why DPDT? I get that half of it is switching the antenna between the TX and the RX. What is the other half doing?
Should I be planning on some failsafe sensors like you did on Fabio II to cut off PTT if bad mojo happens?
Later,
John


Hi John,

OK on all.  Yes, Fabio, the audio work and other things were a trip.  My guideline is this:  It usually takes as long (or longer) to troubleshoot and finally optimize a big rig than it takes to build it. Trying to get operating perfection takes a long time... Wink

See below a sample schematic showing the intended antenna / transceiver/exciter RELAY circuit. You will see why a DPDT or two SPDT relays are needed.  This schematic is a linear with cathode feed -  and yours will be feeding the grid instead. Look at relays  K3A / K3B.   J1 input, J2 output SO-239s.       You will have to figure out your transceiver, driver and/ or receiver switching or whatever outside of the rig.

Yes, sensors to prevent the grid or screen or plate from melting down are a good idea, but can be added later.

You might ask Steve/QIX or one of the e-rig guys what they are currently using for a sequencer board. I am still using the W2NBC design with variable, indepedent keying.  Yes, sequencing is important for sure.

T


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« Reply #88 on: January 07, 2019, 07:52:55 PM »

Phil, I plan to use 1/4 in tube. For current my guess is 450 ma at 2700 volts. Tube sheets don't go that high.

Thanks,
John
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« Reply #89 on: January 09, 2019, 11:56:31 AM »

I read something in the Fabio II thread that I am going to adopt. I am going to make my HV supply general purpose. I have a Drake L4B lineeer that needs a power supply as well. I think I will put a compatible cinch jones interconnect so that I can easily move the supply back and forth. Need to work out the details on this but I think it is doable. I will add a low voltage control line so I can control the hv from a sequencer when running from the 813 rig.
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« Reply #90 on: January 09, 2019, 12:40:29 PM »

I read something in the Fabio II thread that I am going to adopt. I am going to make my HV supply general purpose. I have a Drake L4B lineeer that needs a power supply as well. I think I will put a compatible cinch jones interconnect so that I can easily move the supply back and forth. Need to work out the details on this but I think it is doable. I will add a low voltage control line so I can control the hv from a sequencer when running from the 813 rig.

Hola John,

Good idea, since you will have such a truly magnificent HV supply, might as well use it for everything... Grin

To use a general purpose HV supply in the shack, in the HV supply I mounted a large ceramic "bandswitch" with a knob accessible from the outside.   This bandswitch connects to the HV supply and then distributes HV to each outside amplifier. I can switch the HV to the amplifier in use and this way there is HV only on the amplifier I pick. With a 240VAC primary step start, there is only HV when I key up and only on the amplifier I choose... safety features.

T
    
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« Reply #91 on: January 10, 2019, 10:07:37 PM »

Won that big bandswitch auction so looks like the tank is coming together.

I have a 300pf and a 1150pf variable from my prior design. Think I will hook this up for grins with an RL of 3K and my MFJ antenna analyzer and see if I can get it to resonate on the 4 bands that I am shooting for. Probably will have to add 500pf of antenna load for 160M. I calculated RL assuming 2750v and 450ma. Is that the right current for this design, Tom? The tube datasheet does not go up that high. Also, should I be looking for a larger ammeter than 500ma full scale for the plate meter?

Got to clean it up first.

John
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« Reply #92 on: January 12, 2019, 10:48:53 AM »

Status update - Parts gathering continues.

Still on the hunt for a 500pf vacuum variable and a turns counter. Perhaps a Millen 10030...that would be the cat's meow.

Picked up a Weston 1000ma meter for the plate. Placed a bid on a 500ma meter for the mod. Already have 2 250-300ma ones that will work for the bias and grid. Have a nice Weston 2.5kv meter that I want to use for the HV but my HV is a bit too high. Trying to decide if I mark it as Kv * 2 on the label and calibrate it to 5K. I really don't like to do this, I like meters to read proper correct values. Should I have a filament voltmeter?

Need to spend some time on the bench and check the meters to see if they need external shunts. Betting they do.

Tom, for the 25 ohm 20W glitch resistor, what type should that be? Also looking for a 100K 100W load resistor.

Thinking of building the RF deck on a 17x17x4 Hammond chassis. Honking big but will give me plenty of room above and below. Modulator will be a 17x8x3 or so to mount the tubes with the mod iron on a wood platform to the rear.

Big Midwest Hamfest on the 26th. Planning to attend.

John
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« Reply #93 on: January 12, 2019, 12:48:55 PM »

Won that big bandswitch auction so looks like the tank is coming together.

I have a 300pf and a 1150pf variable from my prior design. Think I will hook this up for grins with an RL of 3K and my MFJ antenna analyzer and see if I can get it to resonate on the 4 bands that I am shooting for. Probably will have to add 500pf of antenna load for 160M. I calculated RL assuming 2750v and 450ma. Is that the right current for this design, Tom? The tube datasheet does not go up that high. Also, should I be looking for a larger ammeter than 500ma full scale for the plate meter?

Got to clean it up first.

John

Hi John,

The 300 pF and 1150 pF tests won't mean a lot since the in-circuit stray capacitance and your later-to-be-found  real-world loading sweet spots will be different. Spend the time looking for that 500 pF vacuum variable and other work instead.  Get the right caps and inductor and everything will fall into place once it is built.  (500 pF and 2000 pF)

Yes, 2750VDC and 450 ma is a good start, though near full strap at 1KW out carrier. Again, once the rig is built, then the meaningful testing and optimizing will start and you will determine where and how you want to run the rig..  My prediction: You will have less than 2750VDC when loaded up to a full 500 ma.  But that's OK - it is what it is. Maybe some added  bigger filter caps will stiffen it up later... we will have to see.

Usually you want the meters to read mid-scale in its normal operating mode, so  1A final and 500 mA mod meters will be OK.  Personally I like 60% of full scale scale operating for mine to give decent resolution while giving some room for "full strap" tuning, off resonance, etc.

T
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« Reply #94 on: January 12, 2019, 01:08:00 PM »

W5UF has these listed as of October and not marked sold.

2 ea. 32 ufd 4.5kv, no PCB, GE, 4X4X10, $45 ea plus shipping.

Thinking I should get one. That will give me 40uF of filter. I have a query out to him on a 10V/10A trans.

John
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« Reply #95 on: January 12, 2019, 01:10:18 PM »

Status update - Parts gathering continues.

Still on the hunt for a 500pf vacuum variable and a turns counter. Perhaps a Millen 10030...that would be the cat's meow.

Picked up a Weston 1000ma meter for the plate. Placed a bid on a 500ma meter for the mod. Already have 2 250-300ma ones that will work for the bias and grid. Have a nice Weston 2.5kv meter that I want to use for the HV but my HV is a bit too high. Trying to decide if I mark it as Kv * 2 on the label and calibrate it to 5K. I really don't like to do this, I like meters to read proper correct values. Should I have a filament voltmeter?

Need to spend some time on the bench and check the meters to see if they need external shunts. Betting they do.

Tom, for the 25 ohm 20W glitch resistor, what type should that be? Also looking for a 100K 100W load resistor.

Thinking of building the RF deck on a 17x17x4 Hammond chassis. Honking big but will give me plenty of room above and below. Modulator will be a 17x8x3 or so to mount the tubes with the mod iron on a wood platform to the rear.

Big Midwest Hamfest on the 26th. Planning to attend.

John

Keep looking - the caps and turns counters are around. Try to get a METAL turns counter. The plasdick ones work, but I have broken a few.  BTW, you can also use a right angle drive and mount the vac cap standing up on the chassis like Chuck's rig. That gives flexibility in placement and will free up some space if needed.

The grid meter should be 50ma full scale?... the screen meter  100 ma?     250-300ma is way too much and the needles will be reading too low for good resolution.  Look up the recommended operating currents and get meters to operate at 50%-60% of full scale or close to this when the rig is running normally.


The glitch resistor can be nearly any type of composition - but a wire wound is probably common and the best choice.  It has some inductance which is a good thing at that point in the supply to keep any remaining RF out of the HV supply.


Yes, the bigger chassis the better. You will always use more than planned, especially when you blow up parts and replace them with bigger, more robust parts. This is a common thing to homebrewing.  Be sure to use some kind of struts to stiffen the panel - chassis junction. Use horizontal rails for the module to sit in when in the rack. (and slide in and out to work on in the rack if possible)  Do not depend on the front panel to bear much of the load.  You probably already know this.   Heavy weight (iron) goes in the bottom of the rack if possible, of course.

4KV might be a good full-scale HV meter range for you when running 2750VDC. You will likely have to calibrate the HV meter and mark it so might as well pick a good voltage range.

Yes, a fil voltmeter is a good idea. I always use a Variac in my filament xfmr primary, so I need it to set the voltage each time.  The Variac is small, so worthwhile.

You are making good progress. Once you get "totally committed," road of no return....... have most of the parts and start the chassis layout phase, I will send you the tubes/ caps/sockets.  Should be shortly the way you are going.   Wink

T

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« Reply #96 on: January 12, 2019, 01:14:10 PM »

W5UF has these listed as of October and not marked sold.

2 ea. 32 ufd 4.5kv, no PCB, GE, 4X4X10, $45 ea plus shipping.

Thinking I should get one. That will give me 40uF of filter. I have a query out to him on a 10V/10A trans.

John

Yes, those would be perfect! If you have the spare cash buy them both.  60% overrated 4500 VDC@ 70 uF in the HV filter is a righteous value!  
With that big plate transformer and big choke, and now big caps, your regulation would be as good as it gets. Build a big class B linear later on and you will be glad you did.

T

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« Reply #97 on: January 12, 2019, 01:27:16 PM »

ok on the caps and meters. One of the meters I have is dual marked 50ma and 250ma so that works for the grid. I will look for a 100ma for the screen.

On the kv meter, it uses an external R so I can calibrate it to whatever I want. I wanted to avoid a printed replacement marking though. They look cheap and get yellow over time. I will keep looking.

There are some millen right angle drives on the bay now. I could use those but I really like the idea of a turns counter. i guess I could look for a vernier knob.

I am getting close. I think by the time I have the heavy iron from Phil I may be ready to start hammering.

I was committed long ago, by the way.

Thanks for the continued help.

John

PS - i need to find a high voltage probe for my knockoff china fluke meter.
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« Reply #98 on: January 12, 2019, 01:39:00 PM »

ok on the caps and meters. One of the meters I have is dual marked 50ma and 250ma so that works for the grid. I will look for a 100ma for the screen.

On the kv meter, it uses an external R so I can calibrate it to whatever I want. I wanted to avoid a printed replacement marking though. They look cheap and get yellow over time. I will keep looking.

There are some millen right angle drives on the bay now. I could use those but I really like the idea of a turns counter. i guess I could look for a vernier knob.

I am getting close. I think by the time I have the heavy iron from Phil I may be ready to start hammering.

I was committed long ago, by the way.

Thanks for the continued help.

John


Good - I think you have the right idea on most everything commented on...


Just to be clear: You will always use a turns counter with a vacuum variable, regardless if the cap is mounted on the chassis vertically or mounted horizontally at the front panel.  

A right angle drive is needed only when the cap is mounted vertically for the 90 degree turn.  


Spend a lot of time laying the rig out. Study again Chuck's rig layout.

T





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K1JJ slogan: 的t takes as much time and effort (or longer) to properly test, modify, optimize & fine tune a homebrew AM BIG RIG as it took to initially build it;
plus the skill to tailor the audio processing & EQing to best highlight our unique voices!"
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« Reply #99 on: January 12, 2019, 05:17:19 PM »

The right angle drives I found are millen 10000 which have a 1:48 turns ratio. Are these the correct parts or will that make the turning painfully slow? i sent a email to Chuck to see if he perhaps has some pics of the underside of that deck pic as well as some for the modulator. His QRZ page only shows the same pic as yours.

John
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