[TenTec] Corsair II warble

[Bob Towers]

Well, the problem is solved, thanks to a lead from Al, WB5JNC. It was not the PTO after all! 
What was niggling me was that I could see that the PTO was capable of better than +/- 5Hz on 10 & 21MHz - the waterfall display of MixW proved it - but why it was worse on the other bands.
I checked the PTO performance on 28MHz and it was rock-stable, the same as for 10 & 21MHz. I looked up the oscillator/mixer section in the manual and these are the 3 bands which have crystals which are 10KHz under nominal frequency, to keep harmonics away from the band edges. The rest of the bands are brought into line with a varactor diode in the PTO (accessed via the SHIFT line) using voltage from a variable resistor connected to the REG line. 
I reckoned that the pot. was dirty/noisy and supplying the varactor with a dirty potential which would account for the warble on 1.8, 3.5, 7, 18 & 24MHz. I rotated the pot to an adjacent part of its range and hey presto, stability on all bands! A side benefit is that the bands are brought into line ie when I switch, say, from 10MHz to 14MHz, the kilohertz values stay more or less the same.
So, in spite of at least 4 rebuilds of the PTO, it wasn't the mechanics of the PTO after all....
I now have a Corsair II which is running beautifully.
Many thanks to all of you, especially Al WB5JNC, for your help and suggestions,
73
Bob
MM3KDZ