David,
Couple of thoughts:
a) is the runing drifting through the heating cycle? f not
then there's probably not too much to worry about
b) if you haven't got access to a fancy infrared radiated
temprature probe, then try the 'templi-laq' (or similar)
heat sensitve paint available from RS. You can put spots
on for 200, 250 etc. degrees and see which changed
colour as a guide to how hot it got
Mike G8TIC
----- Original Message -----
From: "David and Wendy Dodds" <gm4wll@talisman41.freeserve.co.uk>
To: "amps" <amps@contesting.com>
Sent: Sunday, February 09, 2003 12:02 PM
Subject: [Amps] cavity temperature
Hi all.
I'm almost finished putting together a 23cm cavity amp - just a single 7289
round cavity, similar to N6CA's design.
My concern is cooling. I'm using forced-air cooling, which seems pretty
effective in that the exhaust air never gets dramatically
hot, even when running cw for a protracted period of time. What does get hot is
the anode tuning control, presumably due to
convection along the shaft (which is only 1.5 inches long) The Eimac spec sheet
for the 7289 shows a safe maximum operating temp of
250 degrees celsius, so I guess it's ok for the cavity to be pretty hot!
Should I be worried that this is an indication that the cooling isn't
sufficiently effective or am I worrying too much?
I haven't come up with a safe (and cheap!) way of measuring the temperature of
the anode fins. I could probably get to them down the
exhaust chimney, but as they are at 1100v I don't fancy poking a thermometer
down it (even if I had one that went up to 250 deg!)
Any ideas, thoughts, suggestions?
Tnx es 73
de David GM4WLL
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