[AMPS] Dumb directly heated cathode amp operational questions

[measures]

>
>Hi Bill et al
>
>>>2) After I've been running the limit in an SSB QSO what's the recommended
>>>cool down period before I shut the power off?
>>
>>(Rich)  My guess is c. ten-seconds cooldown for unprocessed SSB and 
30-seconds
>>for RTTY.  .
>
>I would suggest more like 3 - 4 minutes, Bill. 

€  The tube weighs about 198g. 

>The 3-500z is a radiation-cooled
>tube i.e.  most of the heat is infra-red radiated by the plate structure,
>and absorbed by the surrounding metalwork, circuitry, glass envelope, etc -
>the blower/fan should keep the tube glass seals at the right temperature,
>but usually does a POOR job of cooling the surroundings.

€  would you like to make a wild and crazy guess as to a commercial 
amplifier that has a perforated black panel next to the 3-500Z/8008 
anodes?.  

>You'll find that it takes anything up to 2 minutes for the orange/red colour
>of a hot 3-500z plate to die away.
>I've rewired all blowers/fans here so that they remain 'on' even after the
>filaments are switched 'off', then switch everything off once I'm sure it
>has properly cooled down.

€  ... you use a thermocouple?
>
>>>That would allow me to not cycle the filaments just for the sake of
>>>getting the noise level down. I could even set up this blower control 
circuit
>>>to run the blower the cool down period after I turn the power switch off

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