Sounds like the load cap is arcing. Take the cover off the amp and inspect it.
Smooth up any burn marks and
Do your self a favor and quit fooling around when tuning up this amp. Decide
the power level you want to use
and pick cw or ssb position on the amp. Preset the tune and load controls.
Using a pulser or cw dits at
40-50wpm, give it 40 or 50 watts and peak the tune and load for max on a watt
meter. Repeat with 100 watts
IF you go from cw to ssb position - retune the amp for max on a watt meter.
Never detune the amp for any reason. Plates are supposed to run red to orange
on those tubes.
I assume the amp is seeing a decent swr.
> I am closing in on 'tuning' an sb-220. To make a long story short I was
> tuning at low power and running it at a higher power. Now I am tuning up
> incrementally in 3 steps from 10 watts to 100 watts CW. This works
> smoothly on both 80 and 40.
> However on 20 when I finished the a 3rd tuning cycle of optimizing
> 'tune' and then 'load' I turned off the exciter drive. Upon re-engaging
> the exciter the amp went ballistic; the sound was a loud continuous
> spitting. It was continuous, not a single snap or pop. I backed the
> power off and re-tuned following the same steps and after turning the
> exciter off and then on it did the same thing. I waited about a second
> looked around the side of the amp. The tube plates were glowing dull
> red. I was able to prevent this by carefully de-tuning. However this was
> more by feel then by a plan.
> What is most likely happening??
> How can it be prevented??
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