>
>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.
>
The thing that one can use is Rp, which is directly related to Q.
>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.
>
However, C-Tune is in series with a much smaller anode-C. Thus, C-Tune
has little effect. Thus, there is not much difference in anode resonant
freq. with different settings of C-Tune.
>
>
later, Ian
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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