Can't Shut Up Audio

[Carl WA1KPD]

I have been restoring a Marconi CSR5A.
 
Love the radio.....
Except like Edith (All in the Family)it will not SHUT UP all the way

I turn the AF gain all the way down and I can still hear sigs
I know that:

• R37, 39, 40, 42, 43, 44, 45, C89 and 90  are OK or new.

• Shorting the grid cap of V6 to ground does not change min vol.

• Replacing V6 has no impact. 

• Even with the grid cap of V6 removed there is still some minimum audio feeding through.

Next stop is C86

Any thoughts?

[K1ZJH]

this might be a worth a shot, since I've seen it happen in antique radios...

Make sure that the volume control, R37, has resistance across the outside legs. If the ground
connection is open to the carbon trace, you will never be able to control the audio gain.
Could be a bad contact between the terminal and carbon track, or an open carbon track??

Pete

[Carl WA1KPD]

Hi Pete
Good thought but even grounding the wiper ends up with some AF coming through....
But where is it coming from?

[w3jn]

Are all those shielded wires going to the vol control and tone control bundled together?  Bet there's some capacitive coupling going on between them if so.

Other thing is the cathode of V6 isn't grounded directly.  C89 is supposed to bypass all audio to ground at the cathode.  If it's bad, there's gonna be audio there even tho the grid is shorted to ground because the diode section of V6 is the detector.  Suggest you replace C89 and also bypass that cap with a .1 or .01 to get rid of any residual RF there as well.