[TenTec] Omni-D, version B, drifting..........................

[Robert Weingaertner]

Ten Tec used temperature compensating caps in the PTO, typically
N750's. Selecting the right value substantially improved warmup
drift. Look at C9, it may be on the foil side of the PTO board.
See if it is missing or damaged. Try different values. Unfortunately,
I don't know where to buy N750 type caps.

		73, Bob WB2VUF


dslosty wrote:
> 
> My recently acquired Omni-D, version B, seems to drift a bit too
> much - at least for my tastes.
> 
> Fronm a cold start, the rig drifts upwards for the next two hours
> with a total drift of around 550HZ. Around 520HZ of the drift comes
> from the PTO as would be expected. The PTO is stable (non-jumpy)
> in operation and I doubt that it needs a mechanical rebuild
> (in terms of the variable inductance).
> 
> The culprit seems to be the digital readout circuitry mounted above
> the PTO enclosure. It generates a fair amount of heat. When the cabinet
> top is removed, drift is cut in half. After around two hours, the drift
> finally stops and the rig stabilizes to the extent stated in Ten-Tec
> specs (around 15Hz/Degree temp change).
> 
> Is the drift of my PTO abnormal? Ten-Tec specs seem to imply
> stabilization
> after 1/2 hour. Two hours to settle down seems a bit long - especially
> for
> running modes like Pactor. There are 4 NPO caps in the oscillator
> circuit.
> Anyone have experience with the aging of these caps?
> 
> This is the first non-synthesized digital readout rig that I've had.
> Perhaps I'm expecting too much....
> 
> Any thought?
> 
> 73,
> Doug/WA1TUT
> 
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