In the Alpha 77Sx retrofit my RFC started out at about 200uH with 18AWG on a
12" Teflon
1.25" diameter form, bypassed at the cold end with 1,000pF at 90KVaR.
Two chokes needed to be added: One, a "VHF" choke, at about 10uH was added
prior to the
bypass cap. Another, a 12AWG on a 1" ceramic form was added at 90-degrees to
the main RFC. This moved the series resonance to 26 MHz on the network. I
then added 680pF
on the cold end of the 10uH choke, and that kept RF from my anode outboard
supply,
but I still added two 750pF HT-57's on either side of a 128uH choke in a
filter in the anode
supply chassis as I run open wire feed for a couple of feet in the shack and
there is some
stray RF that might be coupling to the anode supply wires from cabinet to
cabinet.
The system exhibits no glitches, but I run mostly 160 through 40 at home, so
I can't
report on 20, 15 and 10.
Hal
W4HBM
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Dan Hearn
Sent: Monday, July 17, 2006 9:42 AM
To: g3rzp@g3rzp.wanadoo.co.uk; Mark Hill; Amps Reflector
Subject: Re: [Amps] RF Chokes
Peter, I recall an article I saw 10 or more years ago where a guy was trying
to move the resonance of the RFC in an Alpha amp .He did it by using a
single turn loop of HV insulated wire around the RFC. He was able to move
the resonance into the CB band where it could do him no harm. GL, Dan, N5AR
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
Behalf Of Peter Chadwick
Sent: Monday, July 17, 2006 4:27 AM
To: Mark Hill; Amps Reflector
Subject: Re: [Amps] RF Chokes
Mark said:
>was to have three (solenoid) chokes in series (and
at 90 degrees to one another , if I recall the physical layout
correctly) with one fixed and one switchable bypass capacitor<
Again, a situation where, especially at the LF end of the band, there's an
appreciable RF current flowing in the choke and the bypass capacitor. Maybe
it's just one of those things that you have to accept, and wind your choke
with thick wire on fibreglass or ceramic!
vy 73
Peter G3RZP
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