[Amps] SB-220 parasitic suppressors

[R.Measures]

On Nov 3, 2004, at 4:02 PM, K7RDX wrote:

> 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.

A GS-35b has 0.12pF of anode-cathode feedback C.  An 8877 has 0.10pF of 
it, so they have a fairly similar amount of internal feedback.  Our 
8877 low VHF-Q parasitic suppressor retrofit kit has both an anode 
suppressor and a cathode suppressor.  It comes with a money back 
guarantee.  So far, the only refund has been to a guy who said he did 
not know how to solder.
--  Today's trivia question:  At its max freq of 1000MHz, what is the 
reactance in ohms of the output/input feedback path in a (g-g) GS-35b?

> Parasitic discussion
> sure brings out the pros&cons as well as the snake oil guy(s.)......Jim
> K7RDX
> ----- Original Message -----
> From: "Vic Rosenthal" <vic at rakefet.com>
> To: "Amps reflector" <amps at 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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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org