Hey folks, was wondering if I could have some help. I have a HMV little nipper 61-51 and after a while being on the radios volume suddenly goes loud then back to the set volume again, Then loud again. what could be happening here? it has been restored by a professional so not sure what the problem could be. any help would be great!

Thanks

Steven

One possible cause of random volume variations is bad capacitors in IF cans.

As its been messed with It could be a variety of issues however, if there is a bad connection on the earthy end of the volume control, that is not uncommon. Mica caps will do that as well along with a tube.

Might pay to slip the chassis & take a photo of the innards, so we see what old stuff is still in there.

Marc

What sort of antenna is it connected to?

Radios without internal ferrite or loop antennas and with an inadequate wire antenna tend to pick up a lot of signal from the mains wiring. It may just be that.

If you can connect a meter to the AGC line and see what it does when the volume changes, then we would have a better idea.

Or try running it in another house, see if it does the same thing.

Did the restorer change out the old 2 core power cable and fit a 3 core? If not, that will be the issue for sure.

Thanks for the info, guys, I plugged this radio in again and had it running for about 5 hours and then again for 5 hours the next day and it wasn't till after then that the volume went loud and soft again. I'm thinking it could be a valve because it waits till it gets hot to malfunction? or could it be something else? if it was a cap, why wouldn't it be faulty all the time?

Thanks guys, I really appreciate it .

Steven

Often that sort of behaviour is a Mica cap which can also make snapping, crackling & popping noises like the cereal.

That is often silver migration as it grows whiskers & they get burnt off, more common where there is high voltage DC.

It could be the volume control itself, or thermal related to a dodgy solder joint. Some miniature tubes (6M5) had silver on their pins and that migrated and tracked. Aside from cleaning the top of the socket. I dip their pins & base in Hydrochloric Acid then rinse it.

If you do that make sure you know the tube number & put it back with a paint marker if it comes off.

Valves can lose contact from dirty pins and corroded, or sprung socket contacts. It pays to take / lever the tubes out & put them back to scrape the contacts, if it has been sitting a long time.

Some HMV sets with that general circuit had two 22K resistors in parallel feeding the screens of the RF tubes, that ended up being 10k. That resistor has to be more than one watt, or it fries.

Don't guess, measure!

Putting a meter on the AGC line and noting if the AGC goes up or down when the volume changes will firstly confirm if a fault is after the volume control.

If the volume changes but the AGC doesn't, then we will know there is a fault and we will also know it's in the audio amplifier. That reduces the fault to less than half the radio.

If the AGC becomes less negative when the volume drops, this could be a fault in the RF / IF side of the radio but equally it could be the external signal.

Before even taking the back off, I'd give it a run in a couple of other residences. You may well find it works perfectly elsewhere.

If this is the case we can go looking for issues in the house wiring and appliances.

As a kid growing up in the 50's, the family STC mantle radio would do this. Switching on a light or the instantaneous electric hot water would be enough to double or halve the volume. The thermostat in the fridge is another possibility.

Fitting a 3 core flex to the radio fixed it.

That sort of behaviour with the mains switching often relates to the antenna circuit as well as the domestic wiring itself. Changing the mains loading & devices switching in suppressors, can be indicative of the signal riding on it, or the RF being from the ground. A ground signal could return via neutral as it was tied to earth but as noted a direct RF path to earth via grounding a transformer set was often an improvement.

As said many times; here there is considerable RF riding on the mains and there are strategic line caps placed to get rid of as much as possible. That includes neutral, as after an RCD it is a separate entity albeit at earth potential.

An inadequate antenna has always been a bugbear in towns, most old radios are designed for 25ft of long wire antenna. Never forget that sets with ferrite antennas are directional and need orientating for best signal.

Articles have been written on domestic earthing and some leaves a bit to be desired. I am lucky as the principal grounding is in an old creek bed and others on sheds similar.