TR2/3/3A Question on old radio from my TR3

[TuffTR250]

I've got an old "Automatic Radio model UAF-6270" that was in my TR3 when I got it in 2012. Finally got around to looking at it. I tested it and it is currently set to positive ground and works. I would like to change it to negative ground, the same as my TR3. As can be seen on the pictures below it can be set to either positive or negative ground. However it is unclear to me how to make that change. I don't want to mess up the radio trying to change the ground polarity. I tried turning the "wheel" by the ground indicators on the top cover but it does not seem to want to move. Can anyone advise me of the correct way to change the ground polarity on this radio?

I searched the various Vintage radio web sites but none of them addressed how to change the polarity on this specific radio, and I'm not at all knowledgeable on radios. Thanks!
Bob

 

[Geo Hahn]

On mine (which may or may not have been similar) you pry/pull out a plug with multiple pins that then gets re-inserted in a different orientation.

If it will pull out you would then insert per the notation on the case.

 

[TuffTR250]

Thanks Geo! Did the pull out thing look anything like the round thing in my picture DSCF2023.JPG? I can't tell if that round piece will pull up and out. I don't want to pry up on it in case it breaks it. I will post a picture a little later of the round thng without the top cover over it for a better view of it. BTW, do you have an owners manual for the radio that had the pull out method of changing the ground polarity? Thanks!
Bob

 

[sp53]

Did you look for a very small slide switch to go from pos to negative ground on the outside of the case? my old radio had one.
steve

 

[TuffTR250]

Here is a picture of the ground "wheel" mechanism without the top cover on the radio. Hopefully this is more informative than the picture with the top cover on.

sp53, it does not have a slide switch on the side. I believe the "wheel" mechanism is the ground switch, but I'm not certain, and I don't know how it works.
Bob

 

[Geo Hahn]

Mine had a pull-out plug but it was an old TR3 radio (tubes for goodness sake, had to 'warm up').

 

[Sarastro]

This might help:

It looks a lot like your radio.

I see a notch in the circular thingy that is now pointing to the positive-ground symbol. My guess, based on this video, is that you remove it and turn it so the notch points to the negative-ground symbol.

 

[TuffTR250]

Thanks Steve! Sure looks the same.
Bob

 

[TuffTR250]

Today I received the Photofact service manual in the mail for the Automatic Radio model UAF-6270. It is purely a Service Manual as stated on eBay, not an owner's manual. However, I found in the wiring diagrams a layout of the the ground section. There was an extra small side diagram showing the "bullets" of the ground with a note pointing to it saying "Rotate 90 degrees for positive ground applications". I appreciate the helpful suggestions on the Triumph forums. Since I wanted to order the Service manual anyway, I decided to wait to do the conversion to negative ground until after I had received the Service manual. I appreciate the suggestions on how this ground conversion works. The radio now works on negative ground. Thank you all!!
Here are some pictures of the ground "plug wheel" on my specific radio
Bob

 

[Sarastro]

Interesting. I fiddle with old radios occasionally, but I had never seen that arrangement.

Good that you were cautious. Many of us (ahem!) would just dive in and start prying, and probably break something.