Hi Chris,
Knowing the inductances will help greatly sans
your capability to measure in-circuit resonances.
Since the original coverage was 2-30 mhz. you
can safely assume that the whole choke will work
for you on 160-80-40 meters. The value to select
for the portion remaining in the circuit after the relay
switches should have enough L to cover 30-10 meters
with the resonances parked above 30 mhz. I would
think c. 40 uh would accomplish this requirement.
Keep us posted on your measurements.
(((73)))
Phil, K5PC
Clements Communications and Fire Equipment
410 VZ CR 4903
Ben Wheeler, TX 75754
(903)852-5211
----- Original Message -----
From: "Chris Tran GM3WOJ" <gm3woj@talk21.com>
To: <amps@contesting.com>
Sent: Tuesday, July 02, 2002 9:26 AM
Subject: [Amps] RF choke selection
> Hello all
>
> I've just re-subscribed to this list, so here's a question
> for everyone :-
>
> I'm trying to modify a surplus RF deck (an auto-tune
> 2 - 30 MHz tube amp.) which has a 3-section plate choke.
> One section is short-circuited by a vacuum switch, and
> I guess that this was done above a certain frequency,
> or maybe over a certain range(s) of frequencies to avoid
> choke self-resonances. I've had to remove all of the
> auto-tune control electronics (large parts of it were missing
> anyway) but I need to figure out which bands 80 - 10m need the
> extra choke inductance, and which don't.
>
> Maybe it's as simple as e.g. below 10MHz the vacuum switch is
> open, above 10MHz the vacuum switch is closed. I've tried
> measuring self-resonances using my ancient Heathkit GD1-U
> GDO (that should jog a memory or two!) but I'm not convinced
> by this method. Any ideas how I can figure out the switching
> in/out of this plate RF choke section ?
>
> I have not had time to measure the inductance of each section,
> but I will do this, which will help.
>
> 73
> Chris GM3WOJ
> www.gm7v.com
> www.qsl.net/gm3woj/amps1.htm
>
>
>
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