>
>>>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.
>
? Adjusting C-tune makes little difference in the anode resonance since
C-tune is effectively in series with C-anode, which is much smaller.
>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.
? 'Tis hardly a good idea to tempt fate this close to the ides of April,
Jon.
>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?
? I do not build the suppressors. If L-supp is less than optimal, the
suppression will be as well.
>Last I looked 80 MHz was at VHF.
? zzzzz
>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.
>
? VHF damping the input side of the feedback C and reducing the vhf Q of
the wiring between the anode and C-tune are two of my favourites.
>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."
? not quite. . . When somebody tells me to ignore something, I get
curious . When Hillary told us to ignore the rumours because it was just
part of a gigantic conservative conspiracy to get Bill, I started to pay
attention.
>Paraphrase of Shakespeare: "Methinks he doth protest too much."
? Are you perhaps trying to quote *Hamlet* Act VIII?
>Me: "If someone insists on something too often or too much I begin to
>question it."
>
? I question anything that seemingly makes little sense.
>EVERYONE on this reflector knows that your suppressors claim to lower VHF
>gain in the anode.
? In Wes' measurements, a resistance-wire suppressor lowered vhf Rp and
Q by about 40% compared to a copper-wire suppressor.
>Why continue to harp on it??
>
? Because somebody essentially claimed that Q was not important when
trying to design a dampening device for a resonant circuit. . Because I
have a vague idea of how to spot Not Invented Here Syndrome.
>
- later, Jon
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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