TenTec made a lot of great rigs using the PTO design, but they all seem to be sensitive to having your hand touching or even being close to the metal insert or the metal skirt. Here's what I did to fix that problem once and for all.
The problem is that the PTO shaft that runs through the variable inductor inside the PTO is not grounded, and when your hand gets close to - or touches - the metal insert or the metal skirt on the Tuning knob, it pulls the PTO frequency enough to be noticeable. Move your hand away, and the frequency moves to it's steady value. Bring your hand back near those metal parts on the PTO tuning knob, and the frequency changes.
I decided to try a fix for this at the same time I was cleaning and re-lubricating the PTO in my Argosy 525. For some reason, the 525 seemed to be extra-sensitive to hand-capacitance, so if I could fix this one it should work for any of my other TenTec rigs. I made up a grounded wiper for the PTO shaft. It's made from #22 copper-clad antenna wire, but you could use any lightweight wire or strap that has some spring to it. Phosphorous-bronze fingerstock would be ideal, if you can fit it in the available space. I put the wire under the left (as viewed from the front) PTO mounting screw that goes through the panel behind the front panel (see sketch and photo). There's not a lot of room on the PTO shaft, so the small springy wire seemed to be the perfect answer.
Reassemble the front panel and knobs and give it a test run. Mine worked on the first attempt, and has been working for about a year now without even a hint of frequency pulling. The next time I have to do a PTO clean and re-lube on another TenTec rig, I'll install this grounded wiper at the same time.
If you have any questions or suggestions about this, please drop me a line.
Tnx es 73,
ed - k9ew