Based on N5OLA‘s excellent diagrams, I went through the SB-101 last week and checked all of the resistors I could get to. I found a dozen or so that were well out of tolerance and ordered replacements from Digikey. I’d have used what I have on hand, but all of my resistors are 1/4 W or 1/8 W. I think all of the carbon comp resistors in the Heathkit are 1/2 W, so I ordered new metal film 1/2 W 2% replacements. They’re much smaller than the old resistors.
Yesterday and this morning I de-soldered and replaced the out of tolerance resistors. I also installed a “re-cap” kit to replace a lot of the capacitors in the rig – all of the electrolytics, and many of the tubular paper and resin capacitors. I didn’t get all of them replaced, as some are just a lot of trouble to try and get out. The resin caps I pulled were all testing right at where they should be, though I don’t really have a way to test leakage or ESR. With the part replacement done, I crossed my fingers and fired the rig back up. At first I thought I had no audio – there was no sound from the speaker at all. I turned the function switch to CAL to find the calibrator signal and see if the RF section was working – and hear the cal signal in the speaker! The audio section isn’t dead, the receiver is just way, way quieter than it was before. I tuned around, and from my basement with nothing more than about 3 feet of wire draped over the end o the workbench was able to find the FT8 circus on 40 and 20, and a couple sideband and one AM QSO on 40 meters. I’m pretty stoked at this point. I;’m hoping the cabinet paint from N5OLA arrives soon; I want to get the SB-600 put back together with the new speaker and the power supply re-mounted, then drag it all up to the shack and get the calibrator zero-beat with WWV. I have a little 90s-vintage Radio Shack frequency counter, but don’t think it’s really good enough to nail that 100 kHz crystal oscillator down to the last Hz. And don’t think for one minute that I’m not once again tempted to pick up a “real” frequency counter and maybe an RF generator from eBay…