SB-102 problem

[Brian Wood]

MY SB-102's S-meter was not reacting much to signals that should have been
over S9. I also noticed that the RFG control only caused the meter to go to
about S8, not full scale. So I started digging into the circuit. I measured
voltages, tested tubes, and tinkered with a couple of component values. I
noticed that the grid voltage on V14, the 1st audio amp (6GW8), was low, and
this is also the plate voltage on V13, the AVC diodes and product detector.
It is marked in the manual as 140V, but was actually 35V. I took the tube
out and the voltage returned to normal. So I assumed that the tube was bad,
but I tested it and it came out good. When I put it back in, the RFG control
suddenly worked normally, and a 20 over 9 signal really was 20 over 9. I
suppose the act of removing the tube and replacing it could have cleaned the
pins, but the grid voltage is still way low.

 

Anyone have an SB-102 who could check some voltages around V13, V14, and V3
and V4 (the 6AU6 IF amps)? Or does anyone have any thoughts on AVC behavior
on SB-10x rigs?

 

Brian, W0DZ

 


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