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?
>
>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 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.
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.
>>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.
>
>3-500Z amplifiers with superior cooling to the Henrys are the TL-922 and
>the SB-220. The 220 is definitely the quietest. ''Air system'' sockets
>cause the tubes to operate at elevated temps.
I'm feeling brave today and I'm going to disagree with you again, Rich !
The standard Kenwood TL-922 has one of the worst cooling systems
I've seen - far too little air movement, etc.. !
Consequently, 922s are not very popular with contesters who like
high duty cycles with loads of processing !
73
Chris GM3WOJ
www.gm7v.com www.qsl.net/gm3woj/
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