[Collins] 75A-4 Excessive Audio Level

[Roger Shultz]

The 75A-4 that I have fought my way through restoring electrically and
physically is nearly done but there is one last problem I am in need of
experience or opinions about.

This problem is that my audio output to the 270G3 speaker is just too loud
to be comfortable at anything much above a 1 to 1.5 on the AF gain control.
Even with the knob at 0 there is still some audio leak through.

I have measured all voltages on the first, second and audio output
amplifiers and all voltages are nearly dead on. The one thing I have found
is that R62, the 500K AF gain pot, while it is 500K across the pot, doesn't
reach zero ohms at the minimum position, rather it still has about 50 ohms
of resistance to ground. The actual terminal on the pot is at ground so it's
an internal condition.

I suspect this high resistance to ground would be enough to cause the no
cutoff condition but what have others done to move the range of the AF pot
operational level higher in the scale?

Does anyone have any measurements for AC level that I can use to make sure
I'm not feeding the first audio an excessive amount of gain?

Thanks, Roger NJ2R