<VV> RADIO ISSUES hints and kinks..

[tony.underwood at cox.net]

---- N2VZD at aol.com wrote: 
> the volume control may be "dirty" needing a cleaner sprayed into it as you  
> move the knob back and forth. (you dont need much cleaner , blaster works  well)
> also the control may be damaged by pushing it in to hard? you should be  able 
> to see this if you remove the bottom cover.   


Now, as mentioned in the original reply, sometimes this intermittent audio is caused by the control coupling capacitor failing.    What's more, if the failure is via leakage rather than an open circuit, it can actually damage the carbon wiper element in the control since, depending on where the wiper contact happens to rest, it can run DC voltage into the control through the wiper and actually erode the carbon film off the resist element.    

The trick is to replace this coupling capacitor with a new one (which will be considerably smaller, I do this all the time as a given whether it needs it or not) before it damages the volume control.    

Only seen a few radios have this happen but that was a large enough number to make me arbitrarily replace the caps in these radios if I have one open in the first place for whatever reason.   Likewise all the rest of the coupling caps (as well as filter/decoupling) in the radio... there aren't that many to change out, can do them all in about 10 minutes.    After all this time, the original caps are likely degraded and probably all on the verge of failure if they haven't already.    Replace 'em all.   Also, shunt the power input "can-type" filter cap with tubular replacement caps (will also be MUCH smaller) without replacing the dried out can-type capacitor which is NOT easy to remove; I leave 'em in since they almost never short or leak, they just dry out and lose capacity.   

Once the caps are done, THEN the volume control can be addressed.     

I'd actually suspect something else being wrong here, since an intermittent volume control usually announces its ills with crunching crashing noises.   Intermittent audio that happens without such racket, and without actually touching the volume control itself suggests something else...  although it doesn't eliminate that volume control entirely.  

By the way, it's NOT easy finding a replacement for those old Delco controls, been there done that, actually have cannibalized parts radios for controls because my original factory supply dried up many years ago.    When I inherited all the Delco parts from the shop I worked for Back When, (they'd stopped doing Delco warranty work years before) the factory volume controls were among the first parts to get used up.    

I've actually taken volume controls apart to repair them when possible, using "nickel print" to repair cracks on the ends of the resistor elements where the solder tab is crimped, and swapping out on-off switch parts... anything to get it back into working order without having to scrounge Ebay and/or outta town shops' back-room parts bins for a replacement control.   

Ahh, fun...  

Of course, as mentioned, ask Fred B if he has any controls on hand if it actually does need one.   He has friends in High Places for these sorts of things...   He's professionally into radio repairs and he does good work.   

Hell, I've not done it "professionally" for 8 years, only do it now for friends and associates and chapter members etc. while Fred B is still doing it for a living.  

Fred's an interesting guy to talk to about radios etc, particularly vintage stuff, and not just auto radios.   You should see some of the antiques he has... :) 


tony..