Hi Guys,
I have just acquired a nice looking Radiola with a problem I've not encountered before.
When powered, it can either work fine for a while, or have issues straight up.
The volume control is not crackly, but when it's playing up it will pop when adjusting the volume, much like turning a light on in the house but much louder. When it does this the radio still works, but the audio goes very low volume.

I have tapped all of the valves while in operation, and it doesn't seem to have any effect, but turning the volume will always make pops happen.
If it comes on working fine, then turning the volume up loud will cause it to happen so the audio will drop suddenly, and the problem occurs for the rest of the time the radio is powered.
THere is also some strange noise like slight squealing perhaps that lowers the quality of the existing audio.
I'm just wondering if anyone is familiar with this problem.
I have the full set of spare valves, but it's not looking to me like valves are the problem (tho I haven't yet changed any).
I will make a video of this and youtube it.
Cheers, Art.

What have you not done to it? Very short on specifics here; The volume control sounds like it may be cactus. Squealing is possibly a shielding issue (missing).

If the tired old electrolytics & wax paper caps are still in there, it is a waste of time, fault finding until that has been sorted.

If there is a stage oscillating, the set will be unstable. Replacing & relocating parts, particularly in the Det/Audio can introduce induction, as can lead dress: That destabilises

A chopstick may be a more suitable tool for finding the squeal if its in the wiring.

Marc

It was purchased fully restored. This video is a perfect example:

https://www.youtube.com/watch?v=IXTayB6J8r0.

It's fine and running at the volume it should until it's cranked up, then nothing can change it.
Visually, everything is there.. all valve cans, etc. I wouldn't call it oscillation (the louder than music audio type of squeal).

It's a TRF with three gangs turned by belts so it has a single tuning knob on the front.

It doesn't occur to me that turning the volume up would elicit a problem with inter-stage sheilding when it's fine at low volume, but I certainly could be wrong there.

The volume control is fine though. Once the issue starts, it will persist for the power cycle session, no matter if you return to a low volume.

It looks like a new 45 has done the trick... it can still pop at different places on the volume control, but the audio is staying good.
I'll leave it running for a couple of hours now.

This thread totally messes up the restoration prank I was planning for you lot!

Before:
Image Link
After:
Image Link

I actually have two of these One was fully submersed in the 2012 floods in Ipswich/South Brisbane.
Think I would have tricked a few people? I was planning to come clean though.

Edit Posted as you were posting Art

but I am a noob mate so cant really offer any advice
on valve tech ...thought Amplifies become Oscillators with positive feedback
----.
Not that theres any real help here Art but

Funny(as in strange coincidence)
I just had a strange problem and yet to fully resolve it...more listening required..thought probably more work anyway...I think "if it works dont fix it" is good advice but somethings I think should be a preemptive strike

Intermittent Fault with the sound was my problem ..my first suspect was possibly the volume pot or maybe a flaky 6M5 from reads on that tube

it was at times dropping out (more so from cold) but I could hear the Audio very faintly anyway after doing things like you did
cleaning valve sockets and tapping pots etc I turn it back on the audio was distorted and low and then I heard a crack (possibly a back emf?..upon reflection ...not good) off it went looking for something exploded but nothing
(obviously I had move that wire in the process above)

Then on closer inspection I found out it was the Output Transformer wire wasn't soldered just looked like it was on the speaker side..as I said I've yet to truly pin point that as the cause..it might have something else a miss
(how many years it had been in that state one wonders)

Doubt thats your issue but yours could be in one of those assumed to be ok places too
noob comment here below but possible I suppose
a component that seems fine but under operation is failing
possibly a bad joint or a broken wire making intermittent contact...sounds like its one that might lead you a merry chase

Thought as Marc said, you haven't said what you have done but given what I know of you here I assume you have done the basic procedures..replace waxies electro etc

Oddly you fault description ring bells with a doc on "symptoms and causes" I read but no Idea were that is on the net or can I remember the Likely suspects in the line up for that one

As usual Marc's tips are worth their weight in gold in putting you on a logical thought process to a resolve Good Luck Art...and as always Thanks Marc

It looks like it's solved. It's been running fine since I posted that I changed it.
Maybe the final blast the seller gave it before selling it to me was the last straw for the 45.
I just used the 45 from the other radio.

Good to Hear mate

Edit
OH OK ROFL

Still funny you posting that as I was about to update mine ...

Still fine... I was getting anxious, it was $750.
If the seller knew it had a bad valve he would have changed it I think.

Yeah at that price mate I should hope so but if a collector it could have been sitting for a long time and he didnt know...probably just turned it on to make sure it still worked then off to you

But you'd know better then me

Enjoy mate if its only a valve.. be Happy

Edit maybe I should just change that 6M5 anyway

Worth a try. I try to have a spare set of valves for every radio/amp.
Now I've used the 45 I'll try to get another.
Good luck

Radiomuseum lacks a photo of the 45E. Would you be able to oblige with some?

If a stage has poor neutralisation and is oscillating, that can radiate signal through the entire set. Many of the old sets used a rheostat in the cathode circuit (not looked at a circuit for this) to desensitise the stage by biasing off the valve. If you increase the sensitivity of the valve, where there is radiation, it will amplify it, and perhaps destabilise that stage as well.

Marc

The photo for Radiomeuseum would be something like this:
Image Link
I'm fine with the fact that there's a charge for their service, but that being the case, I'm not at all fine that a contribution from anyone does not contribute at all for that membership.

I'm not sure about the rules for membership, etc, but I can forward photos to a key contributing member who will post them there as long as the owner of the photos is happy for that.

I had in mind photo(s) of the radio itself.

The way I understand it is that membership of RadioMuseum is by financial or material contributions and the more material that is submitted the less money one has to cough up.

Looking at the longer term, if it were popularly agreed that such a project would be viable I would be prepared to host a competing service without charge, perhaps limiting (at the initial stage) the content to Australian radios and televisions. The thing is though, I have very little in the way of content - I could provide the site but I would need a lot of assistance with material. Pictures, circuit diagrams, service manuals, etc. Think of it as a Radio of the Weeks on steroids.