Dave,
I would double-check your HV wiring and measure your diodes to make sure there
might not be a bad one in the chain before you go through the expense and
trouble of replacing all of the filter caps. I have an SB-220 that I built in
1977 and it still has the original Eimac tubes. From 1979 to 2004 I used it on
160 meters with my own conversion. With 230 volts on the primary, I could
squeeze out 900 watts in the low power position and about 1100 + in the high
power position. Your 600 watts seem a tad low but you said that you are using
120 volts in and only driving with 80 watts. Those 3-500's like higher plate
voltage (3500 is ideal) and at least 100 watts drive. To get the most out of it
on 160, a separate input network is necessary. Some just drive it through the
80 meter network using the tuner in their rig but this is far from ideal.
Your plate voltage in the low power position seems abnormally low. Mine runs
about 2400 volts unloaded and swings down to 2000 volts at full current in the
low position with a primary of 230 volts so again recheck all of your power
supply wiring.
My 1977 amplifier still has the original filter capacitors in it. I have
temporarily connected newer and larger electrolytics into the rectifier
circuitry and did not see any measurable difference in voltage output or
regulation. BTW, you should eventually replace the 30K bleeders with at least
double the resistance to reduce heat close to the caps
My 220 soldiers on every day from 80 through 10 including the WARC bands . It
is a fine amplifier if it is not abused by long, continuous full power
operation like RTTY!
73, Dennis W0JX
Milan, OH
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