[R-390] Cosmos Drift

[Tim Shoppa]

I agree fully with Roger here: 1000 Hz drift on a PTO over 3 days is not
a big deal, especially after a major overhaul (probably some parts are
outgassing etc.). This is exactly what the "ZERO SET" adjustment on the
front of the radio is for. If the PTO is wiggling up and down 100 or 200
Hz over a very short time frame (something that can seriously impair SSB
or RTTY operation) then it IS a big deal if you care that much
(listening to AM you'd probably never notice).

ON THE OTHER HAND I've overhauled some Cosmos PTO's and on the bench (NO
KNOB, NO GEARTRAIN) they have stayed steady to 50 Hz over several days,
but only AFTER many hours of burn-in. This is checked with a GPS-locked
OCXO (to invoke an instrument that a technician of the 50's or 60's
could only dream about!)

One factor that I allude to above, is that when the PTO is mounted in a
390A is that the PTO is hooked to the geartrain. Now the PTO shaft is
supposed to drive the geartrain, but in real life there will be some
mechanical backlash feeding back into PTO shaft rotation.

Very often the 17MHz crystal is a kHz or two off nominal and in real
life that's going to be a bigger deal than the PTO drifting a kHz over
days.



>>> <Flowertime01 at wmconnect.com> 08/30/06 9:02 PM >>>
Jon,

I think Cecil hit it with the new tube idea.

However, as operators we never tried to keep a R390/A on a frequency for
days.
A 1000 Hz drift over 3 days ain't all that much unless you are doing 

SSB.

All that care you gave that PTO may take some time to settle in.

Some of it may be your freq counter settling down. 
How often do you run it 3 days at a time?

Leave the receiver on and get some time on the tubes.
30 days 24 x 7 minimum. 

Then check the drift.

Roger AI4NI
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