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Homebrew a plate choke for 4-1000 GG with warc




 
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Author Topic: Homebrew a plate choke for 4-1000 GG with warc  (Read 1508 times)
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KL7OF
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« on: October 17, 2020, 07:47:35 PM »

I've built a 4x1 GG that is warc capable...10-75 meters......anyone have a Plate choke design that I  can wind that is full scrote capable at  5-6 KV?? On PVC wud be great...
Ive been testing with a Johnson 175 but its not gonna cut it...   Tnx.... Steve
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KD6VXI
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« Reply #1 on: October 17, 2020, 07:53:04 PM »

I dunno about pvc.....  I've seen more than one melt down.

Delrin rod is cheap on ebay in pieces.

--Shane
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Detroit47
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« Reply #2 on: October 18, 2020, 12:22:38 AM »

Shane
I like the microwave test. Put a sample of plastic in question in the microwave for a minute.  If there is no heat its ok to use.

Johnathan N8QPC
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kc2we
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« Reply #3 on: October 18, 2020, 08:50:21 AM »

Good source for Delrin rod material is McMaster Carr. I'd use the white Delrin (trade name for Acetal Plastic). Stay away from anything Nylon. Nylon is not a good choice in high RF fields. Several commercial ham radio insulators use Delrin. Delrin is good up to 180 degree F.
Specs from McMaster Carr site:

Color: White or Black
Temperature Range: -20 to 180 F
Tensile Strength: 10,000-11,000 psi (Good)
Impact Strength: 1-1.5 ft.-lbs./in (Poor)
Hardness: Rockwell R120-R122 (Hard)
For Use Outdoors: No

https://www.mcmaster.com/acetal-rods/shape~rod-and-disc/wear-resistant-easy-to-machine-delrin-acetal-resin-rods-and-discs/performance-properties~electrical-insulator/

The cost is reasonable. KC2WE
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Seth Taylor
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« Reply #4 on: October 18, 2020, 08:52:36 AM »

Forgot to mention, Delrin is very machinable, so one could tap a hole in the plastic to install a terminal screw to secure the end of the winding.
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Seth Taylor
KL7OF
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« Reply #5 on: October 18, 2020, 10:15:42 AM »

Thanks...I am flexible on core materials, but I am more interested in a plate choke winding design that will accommodate 10 thru 75 including warc bands...I have used the RF Parts 1inch Delrin rod choke with spaced windings and it has hot spots on 17 and 40. A  Johnson 175 will burn up if you force 17 meters on it...One of you guys must have a winding pattern that works and that I can duplicate....Just being lazy.....
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KD6VXI
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« Reply #6 on: October 18, 2020, 10:35:58 AM »

That's odd you have problems with the one at rf parts.

That's Ameritron's choke.  Same one in all the legal limit amps.

That's what I've used on the multiband amps I've built.

Depending on installation, it has a beautiful resonance in the CB band as well.

--Shane
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KL7OF
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« Reply #7 on: October 18, 2020, 11:23:52 AM »

This is the RF parts choke in another 4x1 I have here...used mostly on 40.....5KV...Nice hot spot in the middle...


* choke.jpg (118.06 KB, 810x1080 - viewed 150 times.)

* choke.jpg (118.06 KB, 810x1080 - viewed 126 times.)
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KD6VXI
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« Reply #8 on: October 18, 2020, 02:13:30 PM »

Damn.  Those chokes are usually pretty stout!

Those 4-1000s sure are pretty tubes!

--Shane
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kc2we
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« Reply #9 on: October 18, 2020, 04:16:07 PM »

I'd be sure to use Heavy Formvar coated wire. Also, an old trick is to wind with a spacing using monofilament fish line or thin cord, coat the winding with an insulating varnish and then remove the spacing line after it's dry. Then u have some spacing to avoid a flash over. Recoat again. One should check the performance and inductance at various frequencies. Seth KC2WE
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Seth Taylor
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« Reply #10 on: October 25, 2020, 12:02:56 PM »

That's odd you have problems with the one at rf parts.

That's Ameritron's choke.  Same one in all the legal limit amps.

That's what I've used on the multiband amps I've built.

Depending on installation, it has a beautiful resonance in the CB band as well.

--Shane
KD6VXI

W8JI read me the riot act about using the ameritron choke  with > 4 kv.   I have 2 x new ones, and they are rated at 1.5A  CCS  @  4.5 kv.
I tested one of them with low dc volts with my small lab  supply.   Stone cold with 1.5 A .  Increase to  `1.6 A...  and it heats up..and fast.  1.7A  and it's  blazing hot.  It goes into thermal runaway real quick like.

Higher B+  voltage stress a plate  choke  real  bad. The peak  rf voltages  in the middle of the windings is through the roof, depending on the band.

To keep it real simple, for a 80-10m amp, a  50 uh choke will series resonate at 40 mhz. Heath used a 50 uh choke on the sb-220.   Buddy used a 50 uh  hb  choke on his  YC-156.  He used  20 ga magnet  wire on a 1"  solid  teflon form.   6700 vdc  no load on a 10 kva  supply  I built  years ago..and sold to him.   Zero plate choke issues  on  80-10m, including all 3 x warc bands. 

A  50 uh plate choke is easy to wind.  You can also use teflon coated  wire.

Jim   VE7RF
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KL7OF
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« Reply #11 on: October 25, 2020, 12:28:26 PM »

Thanks Jim......I read W8JI's blog on chokes and how he does it....I don't get the results he gets using his methods....there is too much voodoo ...I will be winding a straight 50uH soon for testing....at 5-7 KV
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VE7RF
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« Reply #12 on: October 25, 2020, 01:33:48 PM »

Thanks Jim......I read W8JI's blog on chokes and how he does it....I don't get the results he gets using his methods....there is too much voodoo ...I will be winding a straight 50uH soon for testing....at 5-7 KV

His method,  using the T splitter, and small 12 vdc  bulb actually works good.   He now uses a VNA to do the tests.  Both methods are bettre  than  shorting the  choke and using a grid dip meter.

Several folks will  use  112 uh....  but it gets  tricky, parking  series resonance points.   The old  B+W 800  would sometime blow up on 15m with  4-1000  amps.  Mine didn't on my 4-1000.  Contest club  blew there B+W  800  on  15m ssb.   The fix back then was to remove just 4 turns from the  top of the  B+W 800.   As  is, the  B+W  800  resonates just above  21.450  With 4 turns removed...that shifts the resonance up to almost 24 mhz.... where  it will blow up.

W8JI  used a massive  112 uh hb plate choke on his 3CX-15,000A7  GG  AM linear amp, wound with 14 ga magnet wire.
But that amp only covers 3-22 mhz. (and 8 KV loaded).

On any  80-15m  amp, 70-80 uh  works  fine.   If it covers  80-10m,  50 uh is a sure way of zero issues.  You can probably increase to 60 uh, and still  have the 1st series resonance > 32 mhz.   Typ it will function fine if the  series resonance is at least  5% away from any band u operate on.  In the case of the  60 uh choke, even resonating at  33 mhz puts the resonance >  10%  above  29.7  mhz.

Jim   VE7RF
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KD6VXI
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« Reply #13 on: October 25, 2020, 05:49:20 PM »

Use a 1.5 inch diameter Delrin rod.  Drill a hole down the middle 3/4 inch diameter.  Fill with powdered iron.

You'll have huge L, and the distributed C will be low enough to to keep resonances above where we work.

--Shane
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KL7OF
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« Reply #14 on: October 25, 2020, 07:04:31 PM »

Hi  Shane...I have read about the 1200-1800 uh chokes wound on a ferrite.....(Measures?)..Havent tried it....What about a pc of mild steel round bar...3/4 diameter with a teflon tube around it???   or your idea of drilling out the delrin and insert a pc of 3/4 cold rolled round...?
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KD6VXI
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« Reply #15 on: October 25, 2020, 07:16:00 PM »

I'm not sure it was measures, but possibly.

I've always used Delrin and teflon wire.  It's cheap, Delrin scraps and teflon wire by the pound at the surplus house.

Others have had good luck with wire around screwdriver pieces (sans handle), pieces of wrenches, etc.

Me, if in a budget, the sweeping of a machine shop would work as well.

It's not so much the uh that make these attractive, it's the low Cdistributed so resonances are much higher.  1000+ uh is just icing on the cake.


--Shane
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km6sn
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« Reply #16 on: October 25, 2020, 07:33:22 PM »

Please be aware teflon emits phosgene gas when it burns- extremely toxic. I used to use teflon, but changed to something else when I realized its fatal potential.
Furthermore, it emits PFIB at high temperatures, which is 10x as toxic as phosgene!!
https://www.fluoridealert.org/wp-content/pesticides/teflon.effects.lung.htm
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VE7RF
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« Reply #17 on: October 26, 2020, 12:21:11 PM »

I'd be sure to use Heavy Formvar coated wire. Also, an old trick is to wind with a spacing using monofilament fish line or thin cord, coat the winding with an insulating varnish and then remove the spacing line after it's dry. Then u have some spacing to avoid a flash over. Recoat again. One should check the performance and inductance at various frequencies. Seth KC2WE


They space wound on the old  B+W  800  and it still  resonates at the top end of 15m or just above.   When u space wind, the inductance drops like a rock, so far more turns required..and  C  piles up..and u are back to square one.

Jim   VE7RF
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VE7RF
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« Reply #18 on: October 26, 2020, 12:37:45 PM »

That's odd you have problems with the one at rf parts.

That's Ameritron's choke.  Same one in all the legal limit amps.

That's what I've used on the multiband amps I've built.

Depending on installation, it has a beautiful resonance in the CB band as well.

--Shane
KD6VXI

What bands did u test it on..and how  much loaded  B+  ??

One guy I know used the ameritron  choke on his 3x3 with 5.5 kv loaded.....and it last  12 years, then blew up.  He forgets what band it was on, thinks it was 17m.

The bottom  connection is way too close to the chassis.  Typ  folks will install a pair of  HT-57's, about 2-3"  apart on the chassis,  with an aluminum 1" x 2-3" long  plate between em, on top side.   Ameritron choke is mounted to top side of plate, dead center.  B+  fed to one end of plate.  Bottom lug on choke is  wired to plate.   That elevates the top of the  6" ameritron choke a bit,  more in line with the top of a 3x3..or  4-1000.

W8JI  has come up with a new plate choke, good for 6 A  @  10 kv loaded.   It's  10.5"  long and a 1.3" diam  (including the  20 ga magnet wire).
400 uh, and does not resonate in any ham band.   Resonates at 8.4 mhz,  and I think  16.5 mhz.

I believe it's a 1.2" diam glazed ceramic  form, tapped  for a  1/4-20 thread at both ends.   It can be mounted to the chassis... vert..... or parallel to a side wall  ( 2" away from a side wall).   For parallel  side wall  mounting,   bottom of choke is mounted to rear wall  with  1/4-20 bolt.      Top of choke has a right angle  piece of teflon, notched,  and bolted to side wall.   Has to be supported at both ends to take the weight,  due to length.  It's  not in production yet.   Took him a week  with a vna, and several lbs of  wire, and 10 x versions to get it right.

Original versions  were only  300 uh, and resonated in 3 x places.  Later versions were  400 uh.  By playing with one of the gaps,(gap spacing between  windings),  he managed to get the  upper  2 x resonance points  to combine into just one freq.

He needs to start  cranking em out asap.

Jim   VE7RF
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VE7RF
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« Reply #19 on: October 26, 2020, 12:50:27 PM »

Please be aware teflon emits phosgene gas when it burns- extremely toxic. I used to use teflon, but changed to something else when I realized its fatal potential.
Furthermore, it emits PFIB at high temperatures, which is 10x as toxic as phosgene!!
https://www.fluoridealert.org/wp-content/pesticides/teflon.effects.lung.htm


The  phosgene gas is a myth.  But teflon will  emit PFIB  at super high extreme temps.  Teflon is good to  250 deg C (482 F).   Teflon breaks down  at  350 C (662 F).  You gotta be a LOT higher than  662F  b4 it emits PFIB.

Some folks have had issues using  delrin rod for a  former for plate chokes...with the top melting off.   I just stick with  solid  teflon.  Easy enough to drill and  tap a 1/4-20  hole in the bottom.   Then 2 x transverse holes  for brass  8-32  hardware, to terminate top and bottom of  winding.   

Ameritron /  MFJ  tried using solid 2"  delrin for a roller inductor coil..for their high powered tuner.  The  delrin melted with just a  900 w  cxr  into a dummy load.   The D factor on delrin is pretty lousy.  But a  roller  coil has  RF  going through  it.    A plate choke is supposed to block  RF, so delrin should not be an issue for a plate choke..except for rare cases, where the  winding has  sky high V.... in which case the windings will explode anyway.

Jim   VE7RF
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W1ITT
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« Reply #20 on: October 26, 2020, 01:03:53 PM »

I'll second Jim's comment on the "dangers" of Teflon.  A few decades ago I was running high power resonant ring tests with 9 inch rigid coax.  The device had a breakdown and a big Teflon fire.  When I opened the unit up, the fumes were still under pressure and I got a full blast of it in the lungs.  It was acrid, made me cough and choke, and the next couple days I felt like I had the flu...but without the gastrointestinal complications.  We called Dupont and spoke to one of their corporate doctors who deal with health and safety issues with their various products, and he told me that it would go away without long term complications.  They took my name and details down.  Sure enough, I felt OK after a couple days and decades later my hair is grayer and my belt buckle seems tighter but I survived just fine.
I wouldn't recommend inhaling it as a regular diet, but the only thing that scares me about Teflon is the retail price.
73 de Norm W1ITT
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KD6VXI
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« Reply #21 on: October 26, 2020, 02:20:45 PM »

Jim,

It was on twin 500Z amps, a Gs35b and a couple 8877s I built under duress (I hate that tube).

For 3000s and bigger I wind my own on Delrin with teflon wire.  I've also supplied to a couple guys running 20s, but I never did anything with that tube myself.  Once you start twin tubes, the choke becomes a physical problem....  That's a lot of turns of physically large wire.

The ameritron choke was not a problem on our bands, although I haven't done anything on 160 with it.

Everyone who does anything like this needs a vna.  With the nano as cheap as it is, there is no reason to not have a vna in most shacks......  Although I will qualify that you better use NanoVNASaver for anything other than a single band scan. I have one, as well as a VNWA.  I use the VNWA a lot more.

--Shane
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« Reply #22 on: October 27, 2020, 10:21:26 AM »

I have been messing with the w8ji t splitter and bulb...I am starting to get some results.(none that I like) but the process works for me now...A VNA would be the way to go but I don't want to design chokes....There are those that are much better at it...I await their results....
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KD6VXI
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« Reply #23 on: October 27, 2020, 10:28:47 AM »

https://nanovna.com/

Highly recommended.  You won't just use it for designing plate chokes.


--Shane
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« Reply #24 on: October 27, 2020, 01:09:25 PM »

I have been messing with the w8ji t splitter and bulb...I am starting to get some results.(none that I like) but the process works for me now...A VNA would be the way to go but I don't want to design chokes....There are those that are much better at it...I await their results....

Follow the  W8JI procedure  carefully, it  works.  Twirl the  vfo  till   bulbs lights  up bright.... u  now have  1st series resonance  point.   Then run a tiny flat bladed  screw driver on edge, 90 degs to choke....run up side of choke till  lamp  goes dark.   Bingo,  you now have found the offending winding  area.  Mark it  with jiffy marker..and that is  where the gap is installed.   But the  entire process is a major  PITA.

On his original choke,  it had no gaps, was  aprx  320 uh..and  series resonated at  10.0 mhz....and also  20.0  mhz.   Lower gap installed  to  shift the  10.0 mhz  up to 12.5 mhz.   Problem then was, with the lower gap now installed, the  20.0 mhz  resonace shifted up to 24 mhz.  Then the  upper gap installed..to  shift the  24 khz  up to 27 mhz.   End result, with both gaps installed, uh dropped from  320 uh..down to  225 uh.   Resonates at  12.5 mhz..and  27 mhz.

Folks  have tried to  duplicate the  ameritron choke  (why bother for  $25.00)..and the hb  versions  will  blow up on  lower end of  10M  band.   The real issue is, magnet wire is  typ offered in  4 x different  thickness's of  insulation.  The thicker the insulation, the longer the windings are..and more  choke  C piles on..which shifts  resonance points lower.    If thinner insulation used,  winding length is  shorter,  and  less C, and  resonance points shift higher.   Get the  completed choke close to a side wall, rear  wall, or a metal tube, or even dielectrics,  like glass  /  ceramic vac caps,  or  stator/rotor plates on air varaiable caps....  or tank coils, and C  piles on... and  resonance points  shift  down a bit, sometimes a lot.

It's  all a pita.  The  ameritron  choke is  good.   The new beefed  up version, although physically bigger,  will  be a godsend for the bigger  tubes..and higher  B+  voltages.   That is, if it ever gets into production.   I started on my own version of a bigger choke years ago,  but ran out of patience..and  time.  Buddy across town modified a  rotisserie   so we could wind the chokes. 

We also tried the  creative electronics method, using a relay  to ground the  cold side of a bypass cap  at the junction point of  2 x chokes at right angles.  Big choke is  135-180 uh..and small  choke is  50 uh..and  mounted to top of  big choke..and at  right angles.   Flames  everywhere !    The secret is the cold side of the  center junction  bypass cap has to be  DC  grounded  at all times... but not  RF  grounded.  3 x 1 meg,  3 watt  mofs in series is wired from cold side of  cap to chassis.  Only then is the bypass cap in  true  DC block  mode.   Both chokes used on 160m  only.  With relay operated, and cold side of  cap  bonded to chassis,  NOW the  bypass cap is in the circuit..and larger plate choke is effectively out of the  circuit.  ( we found the  3  megohm  trick in the older alpha  amps..before alpha  switched to the ameritron choke...  Alpha used a spare  bandswitch  contact instead of a relay).

 Then what happens is.... both chokes can't be used on  80 +  40M !  wtf?   Way too much  voltage at the junction point, flame on, arcing contacts on relay etc.   Looks like we just re-invented the wheel.   Creative electronics ( now amp systems  inc) and alpha only use both  chokes on 160m.  The smaller  45 uh choke is used  on  80-10m.   Any  50 uh choke will have it's  1st series resonance point  around  40 mhz.

A  VA3  fellow tried an  interesting config.  He used a spdt  vac relay with  COM   bonded to anode. NC  contact  went to  top of large choke.
  NO  contact  went to  top of  small choke.  B+  fed to bottoms of both chokes.  Bypass caps  at  base of each choke.  On paper, he just nailed it.   Here's  where it all went to hell.   Peak V on the  anode..when  tube driven hard is  almost double the loaded B+.   The RF Voltage developed in the  PI  tank circuit...the  voltage component will back feed   through the plate block cap...and superimpose itself onto the anode..and is in addition to the B+.    Now we end up  with sky high  peak V  on the  COM of the  spdt vac relay.   Issue is, the vac relay only has  limited amount of  peak V standoff capability,  across  it's  open contacts.  And on  RF vac  relays, the peak V rating  decreases  as  freq  increases.   With 7 kv loaded on a tube... peak V, when driven can be aprx 13 kv..which is  a bunch.  The  3  biggest gigavac vac  relays are rated for only  7  kv  at  32 mhz..and higher on  lower freqs.

The above  concept works,  but only on lower  B+  voltages.

Jim   VE7RF


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