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April 3rd 04, 11:40 PM

"Michael White" wrote in message
...
I just got a very nice Yaesu FL-2100B, running two 572Bs in parallel. It
works great, loads 0right up, and put out about 600 watts of RF key down
on
20 meters.

I typically run it at 300 watts by reducing the drive from my exciter, and
run SSTV a lot. After about a minute at 300 watts the plates of both tubes
glow a pretty bright red. It's not so noticable in daylight, but at night
in
a darkened shack it's quite bright, a cherry red.

Idle current is correct. The antenna shows an SWR of 1.5 at my operating
frequency. I am not using a tuner between the amp and the antenna.

Is this glow normal? My tubes have the heavy graphite plates. They only
glow
after a minute of key down CW. On SSB, or keyed with no drive, they do not
glow.

Any help will be appreciated. This is my first experience with this tube.
Thanks.

Mike, N4PDY

Do it this way; Tune amp up normally at full power on SSB mode, or CW
mode.

Note the Grid and Plate current readings.

Reduce drive, as you have been doing. But RETUNE the amp at the lower drive
level. Reducing the drive as needed to maintain a level of 50% or less of
the full output readings.

See if that don't fix you up.

Dan/W4NTI

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