Noisy tuning gang.

[ukcol]

I own a Decca TP75 transistor radio to which I have a strong nostalgic attachment. Although not the same individual set it is identical to one I bought when I first started work, it was the first time I had spent my own earned money on myself.

I bought this one from eBay some time ago and it responded well to a limited amount of restoration. One of the problems was a noisy tuning gang and a spray with a little switch cleaning lubricant solved the problem for a while, but the noise returned after some months. I have given it the same treatment a couple of times since but the problem always eventually comes back.

As with the large metal tuning gangs used in big sets the moving part of the gangs capacitor plates are connected to the rotating shaft. Small leave springs provide an earth path (chassis connection) and these springs become worn, weak and/or dirty.

I thought perhaps if I provided an independent earth path for the shaft I could affect a more permanent solution. My first thought was to attach a wire to the shaft using an old valve top cap connector and connecting the wire to chassis as near to the gang as possible. As this extra wire would be subject to bending I planned to run the wire in a loop to reduce bending.

However when I dismantled the Decca I found there was already a wire spring attached the bracket through which the tuning shaft passed and so the shaft was already earthed?? (See pictures). Not so. The bracket was screwed to the tuning gang but isolated from chassis. Presumably the spring was to provide extra friction in the tuning drive to lower the risk of mechanical drifting.

So my job was much simplified, all I had to do was to add a solder tag under one of the bracket fixing screws and add a short wire to chassis. (Again see pictures).

The result was an improvement at least as good as the temporary spray-clean one. There is still a very slight crackle when tuning that is confined to long wave for some obscure reason, but it is so quiet as to be of no consequence.

[vinrads]

Nice one Colin it's good when a plan comes together, I have repaired loads of tuning capacitors, it's usually the vanes catching this can be challenging and time consuming but satisfying when done .Mick.

[ukcol]

Thanks for your comments Mick.

One correction to my first post; the slight remaining crackle is NOT confined to L.W. It is probably because M.W. is busier and the stations are closer together that makes the remaining low level crackle more difficult to hear on M.W.

[Reelman]

Thanks Colin,
That's a useful tip to be aware of.
Cheers,
Peter