[Amps] Plate Choke Issue

[MU 4CX250B]

Hard to believe a flashover arc could jump over a quarter of an inch.
Maybe there’s a VHF/UHF parasitic of some sort. Did the ceramic just
overheat and crack, or did it shatter?
73,
Jim w8zr

Sent from my iPhone

> On Jan 3, 2018, at 8:26 PM, Jim Thomson <jim.thom at telus.net> wrote:
>
> 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
>
>
>
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