Steve Thompson wrote:
Rich Measures wrote
>>The anode's VHF-resonant depends on the suppressor for Q reducing total
>>Q. It seems to me that system Q involves the tank. The VHF anode
>>resonance has nothing to do with the tank.
>
>I meant system Q to refer to the resonant circuit in question, rather than
>the suppressor alone. In this case, the tube anode, suppressor, tune C and
>interconnections. Do you mean something different?
>
Even the system Q (as Steve uses the term, nothing to do with pi-tank Q)
doesn't tell you what the gain of the amplifier might be at VHF. For
that, you need the load resistance that the suppressor produces in
parallel with the tube anode at VHF - and you can't get that from Q
alone. As I said yesterday, for these purposes Q is a dumbed-down number
that you can't actually use for anything.
Also, it's not quite true that the VHF anode resonance has nothing to do
with the tank. If you actually do the math, the VHF resonance shifts
significantly with the setting of C1 at 28MHz (basically because C1 for
28Mhz is not many times larger than the tube output capacitance). For
typical settings of C1 at lower frequencies, it becomes a progressively
better approximation to a VHF short, as commonly assumed.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
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