[Amps] Parasitics & Filament Sag

[Steve Thompson]

R L Measures wrote:
> 
> On Sep 1, 2006, at 11:46 PM, Steve Thompson wrote:
> 
>>
>>
>> R L Measures wrote:
>>
>>>
>>> On Sep 1, 2006, at 7:06 AM, Steve Thompson wrote:
>>>
>>>>
>>>>
>>>> R L Measures wrote:
>>>>
>>>>>> I hope not, I looked from 1MHz up to around 300MHz, in both  
>>>>>> full   and
>>>>>> part band sweeps. Around the tuned frequency was the only place  I
>>>>>> found repeatable signals. It's a laborious process as a spectrum
>>>>>> analyser (at least the ones I have) is unsuited to catching a  short
>>>>>> duration signal.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Switching the amp between Tx and Rx at a 5Hz rate
>>>
>>>
>>>
>>>> If/when I ever look again, I'll try that.
>>>>
>>>> and disconnecting  the
>>>>
>>>>> RF input coax might help.
>>>>
>>>>
>>>> I didn't have anything connected to the input for any of the tests.
>>>
>>>
>>>
>>> And you were able to see the HF fundamental signal at the anodes.
>>
>>
>> I saw brief glimpses of a signal somewhere close to the tuned  frequency
>> (7MHz), which I assume was ringing in the whole tank circuit.
> 
> 
> Steve --- There are two resonant circuits in the output circuitry,  one 
> HF and one VHF. The HF (near)*-resonant part has a broad, shallow  dip.  
> The VHF part has a sharp, deep dip that can suck a dipmeter out  of osc. 
> when coupled too close.
>  Does make sense that the HF one rings and the VHF one does not ring?
It does to me when I think about the time it takes to go from conduction 
to cutoff with the usual bias switching in a g-g amp.

Steve