I’m going to be honest – I was a little hesitant to power the rig on after cleaning off the boards in the sink and the oven. I’ve done that kind of thing before, even with PC motherboards. I accidentally spilled a can of Coke or Pepsi on one back in the 90s, and had nothing to lose. A thorough and careful washing in the sink, a good rinse, and a day or so to dry off and it was perfectly fine. A PC motherboard, though, doesn’t have 800 Volts on it.
Still, with the tubes re-installed and 24-plus hours since it came out of the warm oven, it was time. I connected the power supply and a speaker, crossed my fingers, and turned on the switch. The ALC meter pegged, as I expected it to, but never went back to zero. What did I break? Oh, no… Oops! RF gain turned all the way down, that explains it. Nope – everything works fine.
But let’s have a little flashback to last night. The main tuning dial drive was still slipping intermittently, and I was really unhappy with it. There just was not enough traction between the pulley and the dial. The cracked and warped drive disk allowed it to slip on the dial’s drive ring. I thought I had a solution, though. I was thinking, the dial drive pulley needs a “tire”, not just a little pinching of the aluminum dial ring between the disks. I have a bag of little silicone O-rings, remnants of a repair I did a couple years back to a DeLonghi automatic espresso machine. Maybe that was a solution. I removed the drive pulley and took it apart. On the end of the shaft is a bronze disk, a thin spacer, another bronze disk, another spacer, and the retaining screw. Helpful tip: That screw may be in tight – and it’s a round shaft. I chucked mine in a drill just to get a good grip on the shaft to keep it from turning as I loosened the screw. I didn’t actually use the drill for anything, just the chuck as a makeshift vise.
I removed the screw and outer disk, and slipped an O-ring over the spacer between tie disks. OK, I tried it without the spacer first and the disks were too tight – they wouldn’t work like that. This is experimental aviation – no, sorry, different post, it’s experimental radio. In the end, I found that a 5mm ID x 2mm thick silicone O-ring was perfect. With the drive pulley re-assembled and re-installed into the rig, tuning is now perfect. It’s silky smooth with no slipping. That O-ring should last at least as long as I do, and if it ever needs to be replaced it’s a common part. I’m sure there are at least one or two other sizes and materials that would work. I have a bunch other neoprene O-rings in a kit I bought from Amazon; some of them would probably be fine. Silicone, neoprene, Viton – whatever. You just need something that’s a snug fit over the inner spacer, and just thick enough to keep the disks apart enough to slip over the dial drive ring.
