[R-390] Stability

[Roger Ruszkowski]

Gordon,

In the day the military turned the receivers on and left them on
for ever. I was common to come time for a 6 month preventive maintenance PM
and find the micro switch was stuck on and the receiver would not turn off.

The only time we experienced warm up drift was after this PM and we
put the receiver back in the operators rack.

But it is a tube radio and has a thermal mass that needs to come to
temperature.

R390 and R390/A are and were considered as stable as you
could get with the technology.

Give yours a 1/2 hour and it will warm up and settle down.

If it does not, consider the tubes first. Todd's point on the
VFO 701 is to be taken as serious. Not all tubes are
equal and it is worth swapping tubes around not just for
the signal to noise but for these drift problems in the
oscillators. 

There is a ballast tube in the VFO and  BFO filaments.
It is there by design.

You have to ask your self, Self how stable is my
power voltage. I lived 20 years in LA and San Diego
counties. Brown out was common during the hours 
I wanted to operate my R390/A. So a little drift that
would be obvious with CW was present.

But it was not a problem with the receiver per say.

It will be hard to judge if the drift is in the receiver tubes. In
a ballast tube with a bright spot. Or in the power line variations.

Roger AI4NI