[Amps] SB-220 Flash Over and 160 Conversion

Dennis W0JX w0jx at yahoo.com
Tue Dec 17 01:42:44 EST 2019

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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