[AMPS] Re: Amp Stability

[Carl Clawson]

> (Roger D. Johnson)

> After following the reflector posts for awhile, I should like
> comments on the following:
>
>  1. The common practice of bringing together the input and
>    output of an amplifier together to a single TR relay.
>    Is there enough stray coupling to adversly affect amp
>   stability?
Assuredly. I once traced an oscillation in a 28 MHz amp to RF coupling into
the coil of the output relay, through the DC power leads to the coil of the
input relay and thence to the input. I didn't realize it was going through
the coils and mounted the relays in separate boxes. It didn't help. Out went
the cheap DC power relays, in came a Dow Key.

>
> 2. The effect of a non-synchronized TR relay. Many exciters
>     deliver RF output before the old style clapper relay closes.
>     Having this relay close with drive applied, coupled with
>     contact bounce, I think could induce all kinds of bad
>     behavior.

Many amps will squawk if you apply bias before the output relay engages the
load. (I know this isn't quite what you asked, but I've seen it.)

Regards, Carl WS7L




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