Fidelity HF45 volume control

[Armbored]

Hello all,

I have been servicing a Fidelity HF45 which I now have working well mechanically. The volume control was horrifically crackly though, so I decided to service it with reference to the below thread:

https://www.vintage-radio.net/forum/...d.php?t=132779

There was quite a lot of crud on the contact parts inside the potentiometer, so I tried my best to clean this up with Deoxit and cotton buds. However, now I am about to reassemble I think there is a problem. The volume control doubles as the on/off switch, so there is a little channel in the pot where the contacts sit when the unit is off. To turn the unit on, some resistance is offered before the contacts slip up onto the track and make the connection. This still works, but I find when I turn the pot maximum clockwise (full volume), there is no stop to halt the volume, so it slips back into the 'off' position, in the small channel. I attach some pics, would anyone be able to tell me if this looks right or if something has gone awry when cleaning this up?

[Edward Huggins]

If the volume pot switches off OK after full anticlockwise rotation, could you just not avoid the full clockwise rotation position? You have done well to disassemble and test this thus far. Failing that you could consider replacing it - but you may have some difficulty in sourcing a compatible replacement and installing it into that flimsiest of chassis.

[Clydeuk]

The contacts should never leave the carbon track. I would expect there should be a stop to prevent this happening, it might be part of the back casing. If the contacts are allowed to leave the track into the recess then in time they may bend and get caught.

I expect the switch part is a completely separate unit that is actuated by the shaft. Perhaps it's not in the right position relative to the shaft? I don't remember ever dismantling one of these but I'm sure I must have done once.

[Armbored]

Thanks for the advice chaps, I will have another look tomorrow.

Much appreciated.

[teetoon]

Hi, surely the stop post is in the metal back casing ? Without the back fitted there is nothing to stop it turning continuously.

David.

[Station X]

Difficult to tell from the pictures, but isn't that some kind of stop cam moulded on to the back of the disc which supports the pot wiper? If so, is there a missing stop pin?

I can't see anythig which looks like a mains switch. Is it inside the back cover?

['LIVEWIRE?']

David (teetoon) is right. There is a pressing in the rear metal case of the pot., which acts as a 'stop'. The projection ('peg!') visible on the lower side of the pot. in pictures 3 & 4 acts to limit the travel of the spindle, and, IIRC, also trips the switch mechanism, when the control is set to minimum. Viewed from the front, turning the control leftwards past the minimum setting should 'open' the switch contacts. Turning it to the right (clockwise from the 'off positon' should close the contacts again. The switch should then remain 'on' for the full 240 degree rotation between min & max resistance.

[Armbored]

Hi all,

Yes David is right, I have put the two parts together just by hand and the stop is indeed in the metal casing.

I didn't want to reassemble and solder it together only to find the fault was still there, so this has been very useful. Thanks to all for the help, it's very much appreciated.

Mike

[Armbored]

Just to finish off this posting, I reassembled the switch/control knob and it's working perfectly. No crackles, just a smoothly operating control and good sound through the speaker.

Thanks to all on the forum for the previous postings and the responses to my query.

Mike