[Amps] Plate Choke Issue

[Jim Thomson]

Date: Thu, 4 Jan 2018 07:21:37 +1300
From: Steve Wright <stevewrightnz at gmail.com>
To: amps at contesting.com
Subject: Re: [Amps] Plate Choke Issue


On 04/01/18 04:28, AJ wrote:
> This time I was able to measure where it blew apart, ~20 uh from end to
> end. I slid the wire off the broken ceramic and slid it onto a new one
> mounted it in the amp to measure. I am referring to RFC-1

<Well, 20uH in series with the tubes output capacitance is resonant on
<about 6-8 MHz.? That might be worth exploring..

<S

##  Nope.   Tube output capacitance between anode and grounded grid is
in PARALLEL with the plate choke, NOT in series with it. 

##  There is no way in hell a 27 / 31.8 uh choke  will have its  1st series resonance
in any HF band.   A  50 uh  choke,  regardless of length to diam ratio, will  always 
have its 1st series resonance  at  35 mhz,  well above the 10m band.  

##  Henry radio, in its 8 K ultra, using the   3CX-3000A7 tube, used a 2 piece plate
choke setup.  Large choke was  180 uh, wound with 24 gauge wire.  Small  choke
was just 20 uh, and wound with 18 gauge wire.  Last production units made   used
a  different 2  choke setup.  The original  180 + 20 uh  plate choke setup was goofy at best.

##  a tube arc on any of the 4 x 3CPX-800’s would not cause the destruction of the
ceramic form he has the smaller choke wound on.  

##  His  larger choke really requires 2-3  x  4700 pf ceramic bypass caps.   
His smaller choke should have its uh increased to 50 uh.   The smaller choke
should ideally use  1-2  x  500 pf doorknob style bypass caps, like a  HT-50
or HT-58 series, which are available in 5 kv..and also 7.5 kv.    

##  I would like to know what bands each choke is used on, and what type
of relay he is using to toggle between chokes. 

Jim   VE7RF