[R-390] R-390, Low AGC Voltage

[Tom M.]

Group,

I have a 390 with a low AGC voltage, runs about half of what my 390A deck runs.

The 503 coil works, AGC amp (V509) amplifies, rectifier rectifies, I've changed
numerous suspect caps, volts look OK, tubes are OK, and yet I still have low
AGC voltage.  When I impose a negative DC voltage on the 3-4 terminals on the
back, the gain goes way down, so I know the controlled tubes are being
controlled.

The radio plays OK except AGC action is not as good as expected.  It loses
control on very loud stations such as BBC 5975.

I'm thinking of running a SS full wave bridge rectifier ahead of the tube
rectifier to boost the rectified voltage, i.e. send only negative volts to the
12AU7 rectifier instead of the AC from the AGC amp output.

Has anyone ever tried this, or otherwise have suggestions about 390 AGC low
level?

73 Tom 

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