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?
> Vic, K2VCO
> Fresno CA
R L MEASURES, AG6K. 805-386-3734
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