There was a write up in QST back in the early 70's about parasitic
suppression in the cathode circuit. Maybe you can track it down and read all
about
it.
I remember it because I was building up an amplifier with a pair of 3-500Z
tubes and decided to give the circuit a try. The first time the amp was
fired up it took off like a scalded dog! Maybe some fine tuning was need but I
installed anode suppressors instead and the problem went away.
73,
Gerald K5GW
In a message dated 7/29/2010 6:17:30 P.M. Central Daylight Time,
audioguy@charter.net writes:
I was thinking (perhaps in error) that if the parasitic network was
right at the cathode connection it might be more effective in the case
where there was imperfect shielding between the goesinna and goesoutta.
(quite often the practical case)
In any case, I'm interested in moving the parasitic network to the input
for all the reasons I remember seeing here, plus mechanical stability
and convenience. For example, my Henry 3KA (2x 3-500Z) needs occasional
attention to the suppressors to keep it from oscillating. I would love
to replace the suppressors with silver-plated strap and add a parasitic
network to the input. It would certainly be more robust mechanically, if
nothing else.
73, Jim N7CXI
Bill, W6WRT wrote:
> ORIGINAL MESSAGE:
>
> On Thu, 29 Jul 2010 12:40:34 -0700, Jim Barber <audioguy@charter.net>
> wrote:
>
>> Interesting... What about a series low-pass instead right at the
>> cathode? It would have to handle the drive power, but wouldn't it
reduce
>> the number of potential feedback paths?
>
> REPLY:
>
> I don't think it would reduce the impedance at the VHF parasitic
> frequency, if I understand you right.
>
> 73, Bill W6WRT
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