[Heathkit] SB-220

[Don, W4YCH]

To: WB8JKR, K1ZOK & KM1H,

Ya'll responded to my post concerning the SB-220 that I could not get any 
output or idling plate current when the antenna change over relay was 
energized.

Well, Yesterday I found the problem...I had checked and replaced the zener 
diode, checked all the resistors R1, R2 & R3 on the meter board, checked 
continuity from the plate caps back through to the positive side of the 
capacitor bank,  checked the ground side of the power supply, measured plate 
voltage, checked the RF chokes on the grid of the 3-500's ( they were 25.5 
ohms).

I ran out of things to look at and try so as a last resort I jumpered the RF 
chokes on the grids and bingo! Energizing the relay showed about 90 ma. 
plate current in the tune position, and about 120 ma. in SSB. Hooked up a 
transceiver, tuned into the amp and with about 110 watts of drive I get 
almost 1300 watts out.

I guess either one or both of the chokes opened up with current drawn or the 
grids were above DC ground enough to not let the tubes conduct when the bias 
changed. Ya'll may have more and perhaps a better explanation for this.

Anyhow, I appreciate all of the suggestions.

73,
Don, W4YCH
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