Jim, Manfred, Mark, Vic et-al
Sorry people been busy.
On Wed, 3 Jan 2018 19:26:52 -0800
"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.
Interesting that Henry had a 20 uh choke for 20,15,10. That seems to be
where it blew apart.
>
> ## 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.
This would require me to add another relay at the feed point if I
understand you correctly.
I have wound a 19.5 and a 50; will first attempt the 50.
>
> ## I would like to know what bands each choke is used on, and what
> type of relay he is using to toggle between chokes.
This RFC1 is used on 20,15,10. RFC2 is used on 160,80,40.
The relay is a G43C232.
>
> Jim VE7RF
>
Hi people
Ok here's what I have found.
I checked the relay, Manufacture says
Across Open Contacts pF 1.2 measured 1.19
Contacts to Ground pF 1.2 measured 1.18
Relay resistance contact
Max @ 1A, 28 Vdc 0.02 Ω
Measured .012 Ω
Measured V1 plate to chassis 10.99 pf
Measured V2 plate to chassis 10.81 pf
Measured V3 plate to chassis 10.97 pf
Measured V4 plate to chassis 10.69 pf
This seems normal.
Hi-potted the tubes just make sure there are no issues. 1.2 - 1.4 @ 7kv
Checked the doorknob caps in the tank and bypass for shorts, cracks,
carbon tracks, capacitance values. None found.
I took a couple of the ceramics I have used and tossed them into the
microwave for a few seconds at first and then 10 secs and then to 5
minutes no heating was measured. I have not put the broken ones into
it. Naw thanks but no thanks.
Tested the choke in the amp and out of the amp without the connection
to tube or hv. There was .1 uhy difference that could be my zeroing
difference. It has 2.1 pf of capacitance 32 uhy where it is mounted.
Will check it with the 50 mounted.
Just a notation to everyone reading this the choke in reference in
inverted. The voltage comes in the top and out the bottom to connect to
the relay to switch the chokes. There is 1.5 inches to the chassis from
the hot point.
I have not figure or checked the Q, that I should do . . .
I will attempt a power up and heat check of the various components (ir
gun)
A flash over to the chassis through the ceramic insulator to the ss
bolt is possible, it was excessively long and reused. I have ordered
some ceramic bolts to eliminate that possibility.
Heck all I need is a Phantom Flex and video it. :(
I will update with more info.
Thanks to all that replied, I will keep this updated as time
happens. Any other suggestions appreciated, makes the grey matter
fire.
Sincerely AJ___ VE3HJ
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