[Amps] Initial test of 813 amplifier

[Vic K2VCO]

On 8/15/2010 6:01 AM, Rick Stealey wrote:
>
> Vic, I think if it is an HF oscillation the plate tank components will have a
> large effect on it, whereas if it is a parasitic they won't. In fact, if it is an
> HF osc you can probably stop it entirely by adjustment of the tuning
> and loading caps.

That's what I observe.

As several others said, there are plenty of feedback paths, especially without the 
shielding. When I adjusted the neutralization I got a significant dip in RF feedthrough, 
but it didn't go to zero. So I think there is too much feedback and it is an HF oscillation.

After I add the shielding, it will be interesting to see if the neutralization appears 
more complete (that is, if the RF feedthrough is significantly less).

Old-time grid-driven triode amplifiers used to be built without shielding (before TVI). 
But a tetrode like the 813 has way more gain.

I appreciate all of the comments, which give me the impression that I'm on the right path!
-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/