Hi All

First time poster on the forum! I'm a long time tinkerer of things, still pretty young in my 30's but I like trying to mend things.

I got the attached radio from my grandfather when he passed away. I know it has no monetary value but it means a lot to me as I remember it beside his bed etc.

Potentiometer

The volume control has a built in on / off dial.

It has an issue where once you switch it on it goes straight to a really loud volume and you can only really have the radio on or off and you can't move the volume potentiometer to change the volume. I figured the potentiometer must be faulty.

I probably made a bit of a mess with it but I took apart the radio as per the photos and I was thinking with my soldering iron I could try and use some desolder braid and try to take out the current potentiometer and replace with a new one.

It's a 5K ohm potentiometer (says on the side) with a on / off component built in. What would be the best place to buy a matching one ? I looked on Jaycar's website but it looked they didn't have potentiometer with the on / off switch built in.


Radio Tuner Thread

Also when I took it apart I ended up loosening the front panel with the tunder dial and thread and its a bit of a mystery to me how I would thread it back together. I found a few resources online but nothing really conclusive on how it threads together.

Any online resources with a diagram on how it might need to be re-threaded ?

Thanks in advance for any feedback
Ted

Here's one local source of such a pot pot (interestingly with the switch mechanism exposed like yours): https://www.minikits.com.au/POT5K-16LOGA-SW

Here's another source: https://www.wagneronline.com.au/miniature-potentiometer-switched/resistors...

Note that these have splined shafts, whereas yours has a D shaft, so the matching knob would be an issue.

Photos uploaded.

Thanks GTC

Yes it has a splined shaft and the dials just pull off. Both volume and tuner dial.

The chances are the switch is alright, and has just been bridged out.
The potentiometer is probably OK as well. Undo the thee contacts and check out with a multimeter.
The dial drive cord just needs you to have a good look at it and work out how it should work, and experiment if necessary.
JJ

Yes I meant to say it has a D Shaft

Yes it has a splined shaft

The photos you supplied show two D shafts.

Hi Johnny

Thanks for the info, what do you mean check if the switch is "bridged out" ?

Thanks
Ted

Because of the angle of the shot, photo #4 at first glance gives the impression that the switch has been bridged out, but photo #5 clearly shows a black and grey (or white) wire to each contact.

Sorry yes on very close inspection switch is not bridged out.
But check the pot with a multimeter first. It may not need replacement, just cleaning.
Not with WD40, but if you have nothing else turps or kerosine will suffice.
JJ

Thanks Johnny

No the power wires (black and white) dont' touch each other or anything like that.

What about one of these products from Jaycar, are they good

https://www.jaycar.com.au/deoxit-gold-contact-cleaner-rejuvenator-aerosol/p/NS1434

https://www.jaycar.com.au/contact-cleaner-lubricant-spray-can/p/NA1012

Thanks
Ted

NA1012 looks OK. I use CRC brand.

NS1434 Deoxit is very good for cleaning metal surfaces, especially valve sockets.

Before forking out on any of that stuff, as Johnny says check the pot out with a multimeter. With one probe on the centre tab and the other probe on one of the end tabs, you should see a smooth progression from zero to 5K ohms as you turn the knob. If it is dirty or worn internally, the reading will be spasmodic.

Thanks guys.

I tested with the multimeter from one end to the middle and the ohms went from 0 to 2k

Then I tested from the other end to the middle and the ohms went up from 0 but the numbers jumped around and went as high as 8k

The pot clearly has D5k printed on the side so I would think its 5k ohm rated


Im guessing that means the pot is broken or would cleaning do anything ?

The pot track is carbon, and after a lot of use or age there are lots of fine dry granules of carbon on the surface of the track.
When the wiper is moved instead of a good contact with the track the wiper moves the dry carbon loose particles and instead of acting as a potentiometer it acts as a carbon microphone.
So, cleaning will fix or some lubrication will stop it acting like a microphone.
This problem can create very loud crackling or jumping to full volume, or both.
JJ

D5K appears to be the part number/category, maybe D shaft 5K ohms.

Given that it may be difficult to get that pot in a D shaft configuration these days, if it were me, I would remove the pot and open it up, being very careful not to have parts explode all over the place by doing that inside a box to catch the bits. Then check out the condition of the carbon track inside.

Then if it's a cot case, you could maybe transfer the original shaft to one of those new pots I linked to earlier.