Greetings, experts and enthusiasts,

I'm more of a vintage computer collector ("vintage" = 1980-2000!) and have done quite a bit of restoration and diagnosis. I've learned a lot about digital circuitry from participation in vintage computing forums. I have a reasonable toolset including 30kHz CRO, but no qualifications or professional experience. I don't know much about analogue radio, YET.

I inherited the Philips RadioPlayer 123 that my family had listened to since 1950 and I use it all the time in my workshop. It has extension speaker in the form of an old caneite baffle-board, and phono input terminal posts, with an adapter to accept RCA line input from a solid-state FM tuner. Not sure I have the right configuration for that input.

I have obtained schematic and component list from Radio Service Manual in the National Library here in Canberra. I have replaced all the paper and electrolytic caps. There are still a few micas in the tone control circuit.

I also have replacements for most valves, all used stock, but they don't seem to eliminate this problem:

In spite of the re-capping, the volume intermittently fades or boosts at unpredictable intervals until the thing has been running for several hours, when it is likely to snap back to full volume. I'm supposing there must be a heat factor. In addition, the volume will sometimes suddenly boost if there is a surge on the power circuit, such as switching on a drill or even a fluoro light.

There's no noise in the volume control potentiometer, so I am thinking that is probably OK, after a dose of WD40.

That's what brings me to this forum. This is my first post, so I've put it in the introduction topic. Tell me if I should have made it to the technical forum.

Any advice on how to locate and eliminate this fault?

I'm happy to provide the graphic files of the schematic and parts lists if anybody is interested.

Thanks for any interest,

Maven

Is it just jumping up and down in volume and not changing frequency (ie jumping off of the station)?

That could well be a bad solder joint, if it's not jumping frequency or a MIca cap that has HT on it.? Even a bad pin connection on a valve.

Marc

I had a radio with very similar symptoms. It turned out to be caused by an intermittently open circuit IF transformer.

Thanks guys - this was the problem worked through in the Tech Talk threads I started on popping 6N8s and on Earthing. I believe now solved by soldering and socket replacement.

Maven