[R-390] OT - a little - Northern SP-600

[Miles Anderson]

My experience has been that this is a symptom of the HF oscillator quitting.
I'm willing to bet that if you try it from a cold start at the high end of
the band it won't work. At the low end there's enough capacitance in the
circuit to make it kick over. Once it starts, it will maintain oscillation
as the frequency is increased. I've also had luck "kicking" the oscillator
by switching between the VFO and the XTAL oscillator positions of the
"Crystal" switch. This is usually the result of a weak HFO tube. My SP-600
was one that had been converted by ITT/Mackay to ISB operation with a master
HFO. I found that disconnecting the lead from the HFO compartment to the
switch reduced the load on the HFO and made it less likely to drop out of
oscillation.

Miles Anderson, K2CBY
16 Round Pond Ln
Sag Harbor, NY 11963
k2cby at optonline.net