[Amps] instability issue - a bit more info

Chris Wilson chris at chriswilson.tv
Wed Mar 27 17:59:40 EDT 2013



> On a suggestion I checked the oscillation with a scope. It agrees 
> with my frequency counter - oscillation around 400 - 450 kHz.

> I failed to add in my first post... when this problem occurred 
> during "normal" operation on 12M, the amp seemed stable during 
> transmissions, apparently taking off at the moment of transition 
> back to receive. That in mind, I am wondering if I should 
> investigate the timing of relay and bias switching. This behavior 
> may suggest the vacuum relay contact on the amp is opening before 
> cutoff bias is applied.

> The other really ugly thing I failed to mention is that this 
> oscillation would then continue until I toggled the amp 
> operate/standby switch to standby. I suspect this LF RF is getting 
> into places where there should not be RF.

> 73,
> Paul




27/03/2013 21:58

I think it's the 2011 ARRL Handbook that mentions LF oscillation in
linears, and I recall it mention input to output coupling issues, I
can type out the relevant paragraph if you think it may assist? It's
way beyond my experience, but I recall it mentions something that
sounds similar to your issues.

-- 
       Best Regards,
                   Chris Wilson.



More information about the Amps mailing list