On Thu, 4 Jan 2018 13:05:03 -0500
MU 4CX250B <4cx250b@miamioh.edu> wrote:
> 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
The first one just fractured a large number of times in the same area.
It shattered at the point of 20 uhy of inductance.
AJ___ VE3HJ
>
> Sent from my iPhone
>
> > On Jan 3, 2018, at 8:26 PM, Jim Thomson <jim.thom@telus.net> wrote:
> >
> > Date: Thu, 4 Jan 2018 07:21:37 +1300
> > From: Steve Wright <stevewrightnz@gmail.com>
> > To: amps@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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