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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 27th Aug 2020, 10:43 am   #1
HowardB
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Join Date: Dec 2017
Location: Staines-Upon-Thames, Surrey, UK.
Posts: 50
Default Ultra Radio: The Missing Mains Plug Issue

Earlier this year, I bought an Ultra Coronation Twin R906 on eBay. This is the one with the faux snakeskin case but the mod described here can probably be applied to similar models.

Unfortunately the original mains cable & plug (at the radio end) was missing, as is usual with these sets. The plug is important because it provides a convenient way of switching the set from battery to mains operation.

[The socket on the back of the radio is mechanically linked to the internal mains/battery switch.
When the plug is inserted, a connecting shaft is forced forward to set the switch into the mains position.
When the plug is removed, a spring forces the switch back into the battery position.]

Without the original plug, it's not easy to switch between the two power sources.

This note details how to get around the problem of a missing plug.
The solution is not perfect but extremely easy to implement.
It will not be to everyones taste, but it works for me!

1. Remove wiring from the socket.

2. Remove the spring from the switch control arm. Secure using a cable tie or similar.

3. Remove the connecting shaft from the switch control arm. It is held on by two screws and passes through the socket.

4. Make a new, slightly longer connecting shaft. It needs to be just long enough to protude out the back of the plug. I created one from a sample Karndean floor tile but you could use anything of the right thickness and stiffness that is non-conductive. It needs to be of the right thickness so as to pass easily through the slot in the socket. Drill 2 holes in the new shaft so that it can be re-assembled to the control arm.

5. Hard wire a new mains cable directly to the radio. On the R906, Neutral to the mains/battery switch S4C, Live to Rectifier.

The mains/battery switch can now be manually operated by pushing/pulling the shaft at the back of the radio.
OK, it's pretty crude, not rocket science etc. but it works.
The shaft sticks out the back of the radio slightly, but doesn't look that bad.

For battery operation, I used 10 x PP3's to get the 85v HT and a PP9 with a small value resistor (24R) to get the 7.5v LT.
All working fine on both AC & DC.

Pictures of the mod attached.
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Last edited by HowardB; 27th Aug 2020 at 10:57 am.
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