[Amps] No parasitic choke question

[TexasRF at aol.com]

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 at 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 at 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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