[Amps] SB-220 no output

Warren Volz warren at warrenvolz.com
Tue Jul 25 02:59:54 EDT 2017


I ran into another hurdle with the SB-220 and am hoping someone has some wisdom. If I run RF through the AMP without power applied the relative power meter works and I can match my dummy load without issue. Side note, is the relative power meter supposed to line up on the bottom scale with actual forward watts? Ie: 100 Watts = 100 on the multimeter scale? Once I enable my rigs “amp keying” mode and transmit with anything from tune mode to a carrier I see high SWR and 0 output after the amp.

To troubleshoot, I hooked up my DMM and triggered the keying interface so that the relay(s) engaged. I’ve confirmed that both are working correctly. Oddly if I put the DMM in continuity test mode and trigger the TX mode on the amp I get a beep. So, the RF is blocked someplace inside the tank circuit or band switch? That’s my best guess. Or is it possible that a bad tube would cause these symptoms? There is no deflection on the plate meter when I’ve put RF in. Does that mean the tube is being held in cutoff?

Thanks for the help again. It’s challenges like this where I wish I had a local elmer to help out!

-Warren KD5YPH

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