[Boatanchors] SX-88 oscillates.

[McDonald, J Douglas]

I got my "new" old SX-88 working. But it oscillates in the two RF stages 
at some frequencis in the bottom half of each of the top three 
frequency bands. The first two stages is verified by removing the 6U8 
first convertor tube, it still oscillated, but removong either 
RF amp stops it.

I've tried the usual fixes and nothing does anything except connecting
a good antenna or a 200 Ohm or lower resistor to the antenna terminals.
It only oscillates with them open. I've tried extra bypass caps in the three [sic]
associated RF compartments as well as grounding various unused 
variable cap section above the chassis, and adding extra grounding straps 
between the various (except for straps) insulated boxes.  It only oscillates 
at certain frequencies, so I assumed it was parasitic tuned circuits 
due to parasitic inductance, but these tests should find that and don't.  
My next guess is that it only oscillates at certain low frequencies on each band 
because only at those frequencies do all three tuned circuits match 
frequency and phase "properly" (due to minor differences in the tuning caps),

Putting on the top and bottom RF area covers has only a small effect
on the frequencies.


Any more ideas out there? 

Doug McDonald