[AMPS] Parasitic suppressors/another question,

[Jon Ogden]

>>Agreed. Still you can design an HF amp to be unconditionally stable and 
>>test for that condition as well.
>
>€  Tuning the HF tank circuit and disconnecting the hf load have 
>virtually nothing to do with what is happening in the anode-resonant 
>circuit where the parasitic oscillations take place. 

Ah contrair!  You yourself have said that the anode-resonant circuit is 
composed of Ctune.  Is not Ctune in the tank circuit???  
Sooooooo.......tuning the tank circuit DOES make a difference.  

Also, it DOES give one a measure of stability measurements.  In my amp 
(and in others) the amps were made to oscillate by doing this test.  
After proper suppressor design was intoduced (especially Rich's 
recommendations to add a 10 Ohm resistor in series with a 22 pF cap to 
each cathode lead), the oscillation went away and the amp was completely 
stable.  I recommended this to another 4-1000A user and it got rid of his 
zero signal grid current as well!

The test DOES work Rich.  Been there.  Done that.
 
>>> .  
>>>>And if it is with no drive applied and the neon glows
>>>>orange it means it is oscillating on or near the band selected - not so?
>>>>
>>>€  In my experiences, g-g triodes can occasionally oscillate in steady 
>>>state without drive above the grid self-resonance.  In a 3-500Z, this is 
>>>approx. 80MHz. 
>>
>>Well, then those amps have design problems.  Did those oscillations that 
>>you mention from your experience occur with our without your nichrome 
>>suppressors?  
>
>€  Both.  Resistance-wire suppressors lower VHF gain compared to 
>copper-wire suppressors. 

Well Rich, if an amp with your suppressors in it randomly oscillates at 
80 MHz, then your suppressors aren't doing their job are they?  Aren't 
they supposed to suppress VHF oscillations?  Last I looked 80 MHz was at 
VHF.  If they are lossy on 10M (which you say is true), then they should 
be much lossier at 80 MHz.  So how can you say they are working?  Perhaps 
a good anode suppressor design is not the only thing needed in developing 
a stable amplifier.  Perhaps you need other circuit improvements as well.

Also, what does your continually harped statement about the effects on 
gain of your suppressors have to do anything with answering my question?  
 If they really do lower VHF gain that much than your amp shouldn't 
oscillate at 80 MHz.  

And with regards to the continually harped statement on lower VHF gain 
with your suppressors, I will paraphrase a quote from you and a quote 
from Shakespeare and give a quote from myself:

Paraphrase of you:  "When someone insists I go in a certain direction, I 
generally go the other way."

Paraphrase of Shakespeare: "Methinks he doth protest too much."

Me: "If someone insists on something too often or too much I begin to 
question it."

EVERYONE on this reflector knows that your suppressors claim to lower VHF 
gain in the anode.  Why continue to harp on it??

73,

Jon
KE9NA



-------------------------------------
Jon Ogden
KE9NA

http://www.qsl.net/ke9na    <--- CHECK IT OUT!  It's been updated!!!!!


"A life lived in fear is a life half lived."


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