[Amps] Plate Choke Resonances

[Carl]

----- Original Message ----- 
From: "Bill, W6WRT" <dezrat1242 at yahoo.com>
To: "Amps reflector" <amps at contesting.com>
Sent: Sunday, January 31, 2010 1:43 AM
Subject: Re: [Amps] Plate Choke Resonances


> ORIGINAL MESSAGE:
>
> On Sat, 30 Jan 2010 22:27:47 -0700, Larry Benko <xxw0qe at comcast.net>
> wrote:
>
>>
>>I just ran a simulation with a tube with a 3000 ohm impedance and 3000V
>>peak AC on the plate connected to a 100uH plate choke at 10MHz.
>
> REPLY:
>
> The problem with your simulation is that the voltage is held to a
> constant 3000 V. In the real world the "Tesla effect" will cause the
> voltage to rise far higher and that is what causes the smoke.
>
> One real world experiment is worth a thousand simulations, IMO.  :-)
>
> 73, Bill W6WRT
>

Ive made it a point over the years to test any plate choke I could get my 
hands on and build those in magazine or Internet articles.

Almost without fail the ones using larger than necessary diameter wire show 
a pronounced parallel resonance in or very close to a ham band. This makes 
me think that the builder went the brute force method to avoid smoke since 
#22 or 24 isnt needed at 1200-1500W which is what levels they were used in.

Probably the simplest and cleanest 160-10M choke is the old Amp Supply 
version used in all their amps with real transmitting tubes. One size fits 
all. Tests in the 5KW+ LK-800C and other versions with the 3500V tap and 
three 3CPX800A7's show absolutely no heating problems on any band. This 90uh 
choke has 2 1/8" of #26 on an unglazed 3/4" ceramic form, more properly 
referred to as technical ceramic. Im no chemist but Ive been told that the 
porcelain glazed contain some amounts of metal??

Anyway, the series resonances are 12.8 and 49mHz and the parallel ones are 
13.0 and 27.2 mHz. A .001 and .01 uF bypass keeps any pesky RF out of the 
electrolytics and wiring. Naturally, on 160M the tank circuit is involved as 
part of the choke circuit as already mentioned on here many times over the 
years.

Maybe I havent been involved with sufficient voltages and power, Ive stopped 
at 10KW in my commercial life,  but Ive yet to see a Tesla effect from a 
plate choke. Many times in the bandswitch or Tune cap for other reasons but 
nothing to do with choke resonances.

Perhaps the closest Ive been to ham amp choke fireworks is the various 
Dentrons when run on 12M. Remove 4 turns from the top and all is well. The 
1st generation Ameritrons used to do a nice display also when WARC was 
opened. While they were still figuring out a new design I simply installed a 
B&W 802 in order to get customers back on the air ASAP.

Carl
KM1H




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