[R-390] R-390A low audio level with limiter off

[Jacques Fortin]

Hi Leo,

The V507 plate voltage is way too low to be normal.
I believe that C532 developed a high leakage due to silver plating migration.
That can highly attenuate the audio signal as you experience in your set.
Just change C532 for a new 100pF, 300V SM and retry.
As you are there, you can also remove C537.
I made a lot of measurements on this circuit and the signal integrity will be better with C537 removed.
Check also the R527, R526, R532, R533 and R535 resistor values just to be sure they are OK.

Let us know the results.

73, Jacques, VE2JFE in Montreal