Vic is absolutely correct about resistors changing value due to
heat/age/mistuning,etc. Another way to tame especially squirrly amps is to
add a supressor to the cathode side in addition to the usual anode ones. I
read somthing about that idea several years ago and found it effective in
taming my pair of 4-1000`s when running 6700vdc. My hf GS-35b AMP has a
supressor only in the cathode and has been super stable for the last four
years.....AL-1500 Owners might give that one a try. Parasitic discussion
sure brings out the pros&cons as well as the snake oil guy(s.)......Jim
K7RDX
----- Original Message -----
From: "Vic Rosenthal" <vic@rakefet.com>
To: "Amps reflector" <amps@contesting.com>
Sent: Wednesday, November 03, 2004 2:04 PM
Subject: [Amps] SB-220 parasitic suppressors
> One reason that an SB-220 can develop VHF parasitics is the following:
the
> original suppressors use 2-watt carbon composition resistors. These
resistors
> tend to increase in value when they age, and especially when they are
heated.
> If an SB-220 has been used heavily, especially on 10 meters or -- worst
case --
> on 10 (or 11!) meter AM, the resistors will have gotten quite hot and may
have
> changed significantly in value, or even opened up.
>
> If the resistors are discolored, they should definitely be replaced.
>
> --
> 73,
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco
>
> _______________________________________________
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