[Amps] R. MEASURES PRAYERS ANSWERED

[R L Measures]

On Jun 1, 2006, at 8:46 AM, Vic K2VCO wrote:

> R L Measures wrote:
>
>> Shorting the cathode-grid tuned-input of a g-g amplifier shorts  
>> the VHF feedback path that supports parasites.
>
> They are talking about a grid-driven amplifier with link-coupled  
> input and output.

Without a VHF signal being fed between the grid and cathode, VHF  
regeneration is not likely.

> I think their idea is that the VHF grid circuit is formed by the  
> inductance of the grid tuning capacitor's frame and stray capacity  
> to ground.  As far as VHF is concerned, the grid tank coil is  
> already shorted by the low reactance of the grid tuning capacitor,  
> so putting a jumper across it won't affect the VHF behavior much.

The problem begins when the anode-I changes abruptly, thereby ringing  
the VHF resonance between the anode and the Tune-C.  Since ringing- 
voltage is proportional to Q, More VHF-Q is not good news because  
that increases the VHF potential fed back to the input of the tube.
>
>> With the feedback path shorted, the amplifier is sure to be  
>> stable.  As I see it, this procedure is some dude's fable.
>
> They've shorted the HF tuned circuit in the grid, but not the VHF one.

Jumpers don't conduct at VHF?
>
> -- 
> 73,
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco
>

R L MEASURES, AG6K. 805-386-3734
r at somis.org