[jwidner]

Here's a possibility.  If the original 0.1 was shorted, the added 0.5 was a replacement of higher capacitance, for the 0.1.  I would simply remove it from the radio.

Just to update on this 610B circuit.  I tried removing that DYRT .5 capacitor and the tuning was highly affected.  I no longer received any stations, just a little heterodyning sound as I tuned around.  I put it back in and all worked again.

So I removed it and put in a newer .5 mf, 600 v capacitor I had on hand.  It seems the sound and station reception is much better than even when that old DYRT was in there.  It was possibly wearing out - I don't have a capacitor tester - but things have improved with the reception. 

Essentially, there is the .5 uf in parallel circuit to the 400 ohm resister that doesn't seem to be in the original circuit.  Odd that it worked at one time according to the schematic without that capacitor.

Addition is in orange.

   

Jim