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THE AM BULLETIN BOARD => Technical Forum => Topic started by: KL7OF on October 17, 2020, 07:47:35 PM



Title: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI 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
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: Detroit47 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: kc2we 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: kc2we 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.


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF 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.....


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI 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
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF 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...


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI on October 18, 2020, 02:13:30 PM
Damn.  Those chokes are usually pretty stout!

Those 4-1000s sure are pretty tubes!

--Shane
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: kc2we 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: VE7RF 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: VE7RF 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI 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
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF 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...?


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI 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
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: km6sn 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: VE7RF 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: VE7RF 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: VE7RF 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: W1ITT 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


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI 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
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF 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....


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI on October 27, 2020, 10:28:47 AM
https://nanovna.com/

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


--Shane
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: VE7RF 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


Jim   VE7RF   


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI on October 27, 2020, 03:20:45 PM
He should have used one of the big plunger HV contactors.

Plate choke design is an art itself.  I've only begun to understand that statement after building amps and then measuring the chokes in place with the VNA.  Never had a GDO, so this was just one of those "I always used what worked" scenarios.


--Shane
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: VE7RF on October 28, 2020, 11:52:03 AM
He should have used one of the big plunger HV contactors.

Plate choke design is an art itself.  I've only begun to understand that statement after building amps and then measuring the chokes in place with the VNA.  Never had a GDO, so this was just one of those "I always used what worked" scenarios.


--Shane
KD6VXI

I'm seriously  thinking of a  simple   HB  horizontal cam operated plunger setup.   Sorta like a spdt  mini knife  switch.  What else that just might work is a spare  single wafer  model  88  I have packed away.   They are rated for   13 kv  @  60 hz...but that would be marginal..and real  bulky...stray C  etc.

2 x  hb  delrin  plungers, one for each choke would work.   Banana plug on the end of each plunger.   One banana  jack for each choke.   Select  choke  #1...or  choke  #2.

Jim   VE7RF


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF on October 28, 2020, 12:27:02 PM
50 uh for testing at 5kv on 17M


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: VE7RF on October 28, 2020, 03:25:43 PM
50 uh for testing at 5kv on 17M


On paper,  you should experience zero issues.  50 uh should have it's  1st  series  resonance at  40 mhz.
On  3.5 mhz,  50 uh  =    1100  ohms  xl.    5 kv  x .6  =  3 kv       3000/1100 ohms =  2.72  amps  flowing through  the choke..and also the  bypass cap at the base of the  choke.   The bypass cap(s)  should be something substantial to handle  that much current.   Like a pair of  4700 pf  @  10 kv  discs, or what other combo  that will handle 2.72 Amps  @  3.5 mhz.

Even a HEC   HT-57  in  200pf will handle  15A  > 5.2 mhz.....and  12 A  @  3.5 mhz.   And 9 A    at 1.8 mhz.

3.5 mhz  would be the  worse case.  As freq increases, bypass cap  current drops like a rock.... like  1.363 A on 40m...etc.

What gauge magnet wire did you use ?

The  C1  tune cap value will have to be increased  a bit  on  80m.   1100  ohms of  xl  requires   1100 ohms  of  xc  to cancel it out.  IE:  the 50 uh plate choke  will... 'eat'    42 pf from the C1  tune cap.

Jim   VE7RF


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF on October 28, 2020, 03:33:21 PM
Bypass caps are 200pf and 500pf at 7.5 kv...choke is 22 ga.wound on delrin?  Mounted 2 inch above chassis on porch insulator..haven,t tried it yet


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF on November 02, 2020, 08:40:42 PM
Haven't tested the 50 uh choke yet...got distracted by other stuff...the choke measures 51 uh on the wooden bench and 61 uh installed...Ill post the results...stay tuned....


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF on November 28, 2020, 04:23:04 PM
I got around to testing the 50uH plate choke......It measured 50.5 uH on the bench ...61uH installed..   It won't work on 75 meters.  Amp draws lots of plate current with just enough output to tune...  40 Meters is full output, normal operation...  Break for lunch..


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: WD5JKO on November 28, 2020, 06:48:43 PM

Been hammering out some CQ's on 14332/3, a  few takers, but only me on AM.

Reading through this thread, I have a really dumb question.

Why not put the choke on the 50 ohm side of the pi-network?

Sure, that eliminates the plate coupling capacitor on the input side, but that requires the B+ to be on the entire pi-net. A output series cap would be required, but here a quad of .005uf door knobs would do. The tuning cap shells could get an AC ground through a series capacitor to minimize DC arc damage through the capacitor plates. This is done at a low level on the Central Electronics 20A Mixer tuning capacitor, i.e a .005uf cap.

That 50uh choke would be fine on the output side, from 160-10m. 

Yea, I know, a dumb question.

Jim
Wd5JKO




Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF on November 29, 2020, 10:57:40 AM

Been hammering out some CQ's on 14332/3, a  few takers, but only me on AM.

Reading through this thread, I have a really dumb question.

Why not put the choke on the 50 ohm side of the pi-network?

Sure, that eliminates the plate coupling capacitor on the input side, but that requires the B+ to be on the entire pi-net. A output series cap would be required, but here a quad of .005uf door knobs would do. The tuning cap shells could get an AC ground through a series capacitor to minimize DC arc damage through the capacitor plates. This is done at a low level on the Central Electronics 20A Mixer tuning capacitor, i.e a .005uf cap.

That 50uh choke would be fine on the output side, from 160-10m. 

Yea, I know, a dumb question.

Jim
Wd5JKO



Hi Jim....I have been calling around 14340 mid day.....Your question is not really that dumb....It's making me think....I just don't know what to think.    That 50uH choke made the tune cap run out of C on 75 M...time to experiment some more..


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: W2JBL on December 08, 2020, 12:37:16 AM
Working on a hombrew (not by me) GG 4-1000 amp here. The Plate Rf choke was a ham made clone of the AL-82. It fried on 160. Replaced it with another ham made choke that measured 90 microhenries. Works perfcetly on 160, 80, 40 and 20. Six inches of #24 on a 3/4" form close wound.


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: Opcom on December 10, 2020, 11:28:09 PM
Aside from high voltage hazards and the rest, isn't there a choke advantage to leaving the pi coil hot, putting the DC blocker at the cold end, and getting by with a much smaller 'plate' choke to feed HV through the pi coil via the 'cold' end? TMC used to do that. I want to try it.


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: VE7RF on December 11, 2020, 02:24:49 AM
Aside from high voltage hazards and the rest, isn't there a choke advantage to leaving the pi coil hot, putting the DC blocker at the cold end, and getting by with a much smaller 'plate' choke to feed HV through the pi coil via the 'cold' end? TMC used to do that. I want to try it.

A  couple of ways to do this..and one is to feed  HV wire through cu tubing,  BEFORE it's  wound into a tank coil.   Blocking cap  still at anode end....and  exiting HV wire at anode end of tubing is  routed  around block cap to  anode.  That only works on tubing coils.   

If hv wire can't be  routed through tubing, like  edge wound coils, airdux  etc,  and  50 uh choke down at 50 ohm end, the  tune + load  caps + tank coil,  Plus band switch  are all hot with  B+.    Jennings  et  all sez u gotta  severely de-rate vac caps if  B+ is on them...and that's on top of the  existing de-rating  fro  RF.   IE:  15 kv rated cap is the hi -pot rating.  RF rating is  60% of that or  9 kv.  With  B+  present,  it's reduced  down to  5 kv.

Good news is....  W8JI  has come up with a 'big boy'  version of his ameritron choke.   It's  designed for these bigger tubes, and higher voltages.   It's  1.3"  diam  x 10"  long.   Rated  for 10 kv loaded  @ 5-6 amps  ccs.    400 uh.....and does not resonate on  any of the 9 ham bands  from  160-10m.  Does not resonate on 60m +  11m  either.   It's gapped in 2 places.   Took him a week, and several lbs of wire to get it  right.   He just got  50 more (unglazed) ceramic forms delivered a couple of weeks  ago.  He uses a semi lathe device, that also counts the turns....so he knows when to stop, and insert a precise length gap.    Tapped for  1/4-20  at each end.  Transverse brass screw  at each (inboard) end of  choke top/bottom winding, to terminate windings.  It can be mounted to the  chassis..and stoof vertically.   It can  also be mounted parallel to a side or rear wall....as long as it's at least  2" away.

Dunno when they will become available, but they will be a godsend for us  HB folks.  400 uh =  4523 ohms of  XL   @  1.8 mhz.    He sez the RMS  RF  voltage  component is 60% of the loaded  B+ value.   IE: 5 kv loaded B+  =  3 kv  rms.   3000 / 4523 ohms = .663 amps  of  RF flowing down the choke...which requires a big value bypass cap at base of plate choke...like a pair of  4700 pf  @  10/15 kv  disc ceramics.

IF the  bypass cap at the cold end of plate choke is not big enough, like  say a 1000 pf  doorknob used,  ( even if the  1000 pf  doorknob will handle lotsa current on 160m) what happens is.... the  too small a value bypass cap will  only pass  1/3  to  1/2 of the  RF current  coming down the choke...and the rest  goes straight into the  HV filter caps.   

Most of us have tried every  version of a 2 x piece  (big and small) separate  plate choke schem, that's involves a relay.    Problem is, both chokes are used on 160m only..and the smaller  50 uh  choke still has to be used on  80-10m.   Both chokes will not work on  80+40m.... the peak V  at the junction of the
 2 x chokes is  sky high.

Hopefully he will get them available after xmas.   I need  2 of em  real bad.... one for the  3x3 amp...and the other for the  3x6 amp.

Later.....  Jim   VE7RF


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: WD5JKO on December 12, 2020, 10:06:17 PM
A  couple of ways to do this..and one is to feed  HV wire through cu tubing,  BEFORE it's  wound into a tank coil.   Blocking cap  still at anode end....and  exiting HV wire at anode end of tubing is  routed  around block cap to  anode.  That only works on tubing coils.   

   I like that idea about using tubing. For a multi-band rig, maybe a hybrid approach would work. Maybe use a single piece of copper tubing for 10m-15m-12m-17m, and then switch over to air-wound for 20m-40m-80m, and then possible a toroid for 160m. The idea is to thread the HV B+ wire through the copper coil, and from there use a regular plate choke to the B+ that only needs to deal with 160m to 20m. Any parasitic resonances of the plate choke between 14.5Mhz to 30Mhz would not matter as much because the circuit impedance would be 50 ohms at that point when operating on the upper bands.

Would that work?

Jim
Wd5JKO




Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF on December 13, 2020, 09:39:19 AM
Aside from high voltage hazards and the rest, isn't there a choke advantage to leaving the pi coil hot, putting the DC blocker at the cold end, and getting by with a much smaller 'plate' choke to feed HV through the pi coil via the 'cold' end? TMC used to do that. I want to try it.
I have a TMC transmitter with a coaxial plate choke..It tunes from 1.5 to 30 Mhz with no plate choke problems..
I have also ben playing with different chokes on the 4-1000A amp....55 uH worked except for 75 meters..I added another 22 uH and the choke worked fair on all bands...I wound a straight 300uH on a glazed ceramic 1 inch form and it works the best so far..full output on all bands except 10 .  I cant put more than 5 KV on it however because the bandswitch arcs and I need some bigger doorknobs for bypass...more later


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: Opcom on December 15, 2020, 11:39:01 PM
Sounds pretty good. My TMC pi coil is tubing designed to be @7500VDC but I will run no more than 4800.
Impractical to get any sort of HV wire through.

On the caps discussed, how are these older micas for HF with a 3CX3000 at 6-7KW? I'm not ashamed to ask. LOL was never ashamed of driving the speed limit in a fast car either.


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: WD5JKO on December 16, 2020, 09:20:19 AM
LOL was never ashamed of driving the speed limit in a fast car either.

Pat, you still have that /6 Dodge Dart in the driveway?  :P

Jim
Wd5JKO


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI on December 16, 2020, 11:21:20 AM
Sounds pretty good. My TMC pi coil is tubing designed to be @7500VDC but I will run no more than 4800.
Impractical to get any sort of HV wire through.

On the caps discussed, how are these older micas for HF with a 3CX3000 at 6-7KW? I'm not ashamed to ask. LOL was never ashamed of driving the speed limit in a fast car either.


I've seen them used, Pat.  But the TX I saw them in was for the lower portion of HV.  Guy had a 75/80 meter amp with a 4CX10k in them.  Dude had dedicated tens on 160 - 40!  Guess he wanted to have the world hear his CQs.


--Shane
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: K1JJ on December 16, 2020, 12:29:58 PM
Pat,

I have used those older mica caps and still do (QRO) for years up to 20M and never had one pop.  I was told that they become somewhat inductive above 40M, however.  (How wud we test this)  I have used them in PDM filters (100 KHz) and QRO on 20M.  I have faith in them from 160 to 40M.

They are very common from BC transmitters over the years.

As for 10, 15 meters, (and possibly 20M) I would go with the big Russian caps to be safe.

T


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: Opcom on December 17, 2020, 11:24:23 PM
LOL was never ashamed of driving the speed limit in a fast car either.

Pat, you still have that /6 Dodge Dart in the driveway?  :P

Jim
Wd5JKO

Yes I do still have that Dart. I have no time to mess with it because of other stuff and been thinking of letting it go.

-==

On the cap, well, you guys say it's iffy, so I better listen about the freq limitations.

My LCR measurement stuff  -specific purpose instruments -are far short of HF measurements. Maybe the MFJ259 would give some interesting results -if the cap is resonant at some frequency it could be calculated I am postulating.

Also looking at the cap's nameplate -the current rating decreases after a point. Well they make good parts for other gear and otherwise always nice paperweights. For me the offer an additional advantage as a standoff so I was hoping it might work out.


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: VE7RF on December 26, 2020, 04:16:44 PM
Sounds pretty good. My TMC pi coil is tubing designed to be @7500VDC but I will run no more than 4800.
Impractical to get any sort of HV wire through.

On the caps discussed, how are these older micas for HF with a 3CX3000 at 6-7KW? I'm not ashamed to ask. LOL was never ashamed of driving the speed limit in a fast car either.


W8JI uses one on his  3CX-15,000A7  GG  AM SW broadcast amps.(3-22 mhz), 6 kw cxr, 24+ kw pep out.   Look at  CDE's  site.   Although touted as  100 khz  to 3.3 mhz   caps, the  detailed graphs   show another story,  some will   peak for max current at 10 mhz..then drop in current rating  above / below  10 mhz.... and still handle bucket loads of current   up to 22 mhz.    Some will handle a lot oc  current up to lower vhf. 

Folks were saying the mica caps don't like  B+.     CDE engineers  told me  3 months ago, there is  zero issues  running B+ on em, and using em as plate blockers. ...even up to almost rated voltage.   There is no...'chemical migration'  with  B+  applied. 

But u have to use the right cap..  rated to handle the caculated rf current through the cap.... which can be substantial on upper  HF  +  6m.   Very easy to calculate the  rf current through the block cap...on any freq.

Myself,  I use 4 x  200 pf  @  15 kv  HEC-HT-57's for plate blocking on 80-10m.   The  200 pf HT-57 is the..'go to' cap..rated for  15A..each.   I will use  8 of em on a 160-10m amp.   On my own  160-15m  3x3 amp, I used  6 x  500 pf  HT-57's.

Jim   VE7RF


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI on December 26, 2020, 07:08:47 PM
In the past I would use some monster Draloric caps.

Now, with the commie stuff so cheap, caps from China are my go to for 6000 and lower.  They bolt in with M8 terminals and I've passed some pretty big peak and avg current through them at 29 mhz.

Anything bigger I go vac cap from Russia.

--Shane
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF on January 05, 2021, 05:59:10 PM
Aside from high voltage hazards and the rest, isn't there a choke advantage to leaving the pi coil hot, putting the DC blocker at the cold end, and getting by with a much smaller 'plate' choke to feed HV through the pi coil via the 'cold' end? TMC used to do that. I want to try it.

A  couple of ways to do this..and one is to feed  HV wire through cu tubing,  BEFORE it's  wound into a tank coil.   Blocking cap  still at anode end....and  exiting HV wire at anode end of tubing is  routed  around block cap to  anode.  That only works on tubing coils.   

If hv wire can't be  routed through tubing, like  edge wound coils, airdux  etc,  and  50 uh choke down at 50 ohm end, the  tune + load  caps + tank coil,  Plus band switch  are all hot with  B+.    Jennings  et  all sez u gotta  severely de-rate vac caps if  B+ is on them...and that's on top of the  existing de-rating  fro  RF.   IE:  15 kv rated cap is the hi -pot rating.  RF rating is  60% of that or  9 kv.  With  B+  present,  it's reduced  down to  5 kv.

Good news is....  W8JI  has come up with a 'big boy'  version of his ameritron choke.   It's  designed for these bigger tubes, and higher voltages.   It's  1.3"  diam  x 10"  long.   Rated  for 10 kv loaded  @ 5-6 amps  ccs.    400 uh.....and does not resonate on  any of the 9 ham bands  from  160-10m.  Does not resonate on 60m +  11m  either.   It's gapped in 2 places.   Took him a week, and several lbs of wire to get it  right.   He just got  50 more (unglazed) ceramic forms delivered a couple of weeks  ago.  He uses a semi lathe device, that also counts the turns....so he knows when to stop, and insert a precise length gap.    Tapped for  1/4-20  at each end.  Transverse brass screw  at each (inboard) end of  choke top/bottom winding, to terminate windings.  It can be mounted to the  chassis..and stoof vertically.   It can  also be mounted parallel to a side or rear wall....as long as it's at least  2" away.

Dunno when they will become available, but they will be a godsend for us  HB folks.  400 uh =  4523 ohms of  XL   @  1.8 mhz.    He sez the RMS  RF  voltage  component is 60% of the loaded  B+ value.   IE: 5 kv loaded B+  =  3 kv  rms.   3000 / 4523 ohms = .663 amps  of  RF flowing down the choke...which requires a big value bypass cap at base of plate choke...like a pair of  4700 pf  @  10/15 kv  disc ceramics.

IF the  bypass cap at the cold end of plate choke is not big enough, like  say a 1000 pf  doorknob used,  ( even if the  1000 pf  doorknob will handle lotsa current on 160m) what happens is.... the  too small a value bypass cap will  only pass  1/3  to  1/2 of the  RF current  coming down the choke...and the rest  goes straight into the  HV filter caps.   

Most of us have tried every  version of a 2 x piece  (big and small) separate  plate choke schem, that's involves a relay.    Problem is, both chokes are used on 160m only..and the smaller  50 uh  choke still has to be used on  80-10m.   Both chokes will not work on  80+40m.... the peak V  at the junction of the
 2 x chokes is  sky high.

Hopefully he will get them available after xmas.   I need  2 of em  real bad.... one for the  3x3 amp...and the other for the  3x6 amp.

Later.....  Jim   VE7RF
Have you been able to get one of hhe big plate chokes yet?


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF on January 07, 2021, 10:50:20 AM
Check out this 90 degree plate choke for 10 thru 160 meters...very clever


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KD6VXI on January 18, 2021, 04:46:38 PM
https://eaglemade.net/collections/chokes/products/plate-choke-10-thru-160-meters?fbclid=IwAR3lpXM1vWkwtW_m4xqXfNiAvd38zAzDt--AYL0xbOHmID--z8kSdbbWJbA

10-160

As mentioned in another thread, Floyd makes some good stuff.  I don't know where the resonances are, but you could probably email him and find out.

--Shane
KD6VXI


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF on January 24, 2021, 09:32:36 AM
I finalized the design on the 4-1000 GG. Running 6KV at present. Wound up with a 220Uh plate choke wound with #18 formavar on a ceramic core...bypassed with (2) 3300pF  @12KV caps.  The bandswitch problem was solved by switching the coil taps with Russian Vac caps..so simple and works very well.  The amp has great output on 15, 17, 20 40, and 75.  I ran this amp with only a 10 meter coil and was able to get 900 watts on 29mhz with only a little heating of the plate parasitic suppressor.  With a multiband tank installed, 10M performance is dismal..So no 10M band on this amp...


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KA7WOC on January 24, 2021, 11:25:17 AM
My thumb is pointing up


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: W1ITT on January 24, 2021, 06:45:08 PM
It appears that you are using the first three turns of that nice edge-wound inductor for 10 meters.  If so, the Q would be awful, especially having the whole rest of the coil coupled to its field.  Winding a 10m coil from some copper water tubing, then moving all the other band taps down by that many microhenries should get you better results on 10m.  You have enough room for it between the anode connection and the end of the inductor, where that long strap is now.
I like the looks of those commie vacuum relays all in a line.   Dr Alex sells some good stuff.  It's actually a bit more elegant than a big honking rotary bandswitch.  I ran a 4-1000A for about four decades, in conventional grid driven, grounded screen grid driven, and grounded grid.  It's a hard tube to kill, but getting harder to find now.

73 de Norm W1ITT


Title: Re: Homebrew a plate choke for 4-1000 GG with warc
Post by: KL7OF on January 24, 2021, 08:13:29 PM
It appears that you are using the first three turns of that nice edge-wound inductor for 10 meters.  If so, the Q would be awful, especially having the whole rest of the coil coupled to its field.  Winding a 10m coil from some copper water tubing, then moving all the other band taps down by that many microhenries should get you better results on 10m.  You have enough room for it between the anode connection and the end of the inductor, where that long strap is now.
I like the looks of those commie vacuum relays all in a line.   Dr Alex sells some good stuff.  It's actually a bit more elegant than a big honking rotary bandswitch.  I ran a 4-1000A for about four decades, in conventional grid driven, grounded screen grid driven, and grounded grid.  It's a hard tube to kill, but getting harder to find now.

73 de Norm W1ITT
Hi Norm....The relays allow for much shorter lead lengths...I have no 10M capability on this amp...decided against it ...(See Reply #49)  I have several sockets and several more 4-1000s so I will be playing with them...this is the third 4-1000 rig in the shack.  
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