I just picked up a used sb-200 that someone has added all the Harbach mods to. Complete power supply board, soft key, soft start, new t/r relay (it appears) and new fan. Tubes seem fine. Original Cetrons and a new set of matched Taylor’s. Amp puts out good power 500-700 watts on all bands. Seems to work perfectly on 80 and 40. Anything higher 20, 15, and 10, something quite strange happens upon keying the amp. I’m keying up the amp in the correct sequence by hand using a hand keyer. I’m tuning into a dipole that is made “resonant “ with my Ameritron ATR30 matchbox. On 20, 15, and 10, every time I key the amp the swr meter on the ATR30 goes full tilt until the transceiver is keyed and rf drive applied. Once rf drive is applied, the transceiver “sees” good input swr and the tuner shows good output and low output swr. When I unkey the transceiver and then the amp, the swr meter on the tuner goes full tilt again for a split second. I’ve checked nothing so far. I know a few of you on here have extensive experience with these amps. What’s happening here on 20-10? Thanks!