should early 60s radios hum?

[f.cooper]

Hi,
Have you established where the hum is coming from ? from the loudspeaker ? or the radio in general. If the latter it may be coming from the mains transformer. Try listening with the output valve removed.
Nearly all valve mains rardio's of that era emitted a small amount of hum, it depends how sensitive your ears are. Early transitor radio emitted a high pitched hiss, this again depended on how sensitive your ears were as to whether you actually heard it.

[Billy T]

Originally Posted by hkn102l

Only a thought: do you have any other Mains operated radios that you could try in the same mains socket? Does this one display the same symptoms? If it does suspect all the mains devices that are connected to the supply(i.e switched mode power supplies, televisions, cheap thermostatically controlled soldering irons, touch controlled lamps etc.etc)??
There is so much mains borne interference in most domestic situations!
cheers John

Perhaps we could better identify the type of noise being heard? If it is a hum at 50Hz it may be the lamination noise from the transformer, heater-cathode leakage, ground current from filament supplies or modulation hum, and if it is hum at 100Hz it is most likely on the output side of the rectifier so filtering is a possible cause. SMPS noise is more of a hash sound because it has a wide range of harmonics and switching speed is way above 50-100Hz. Thermostatically controlled items usually just produce crackles, clicks, buzzes and pops.

You can sometimes get a better handle on the problem by just flicking off the switch at the wall (or unplugging from an extension lead) while listening for any change in noise level or characteristics before the HT dies. If it just drops dead because of low storage, temporarily connect another 10-20 µF cap on the output side of the HT filtering (not the rectifier side) to help the HT stay up a few seconds longer. Unfortunately most noise sources will stop the instant the mains goes off, so it a wildcard option at best, but it can give clues.

Cheers

Billy 8-{)

[chokesrule]

Hi, Thanks for all this input!.I am still awaiting my circuit diagram BUT it is plain somebody has been in here before me. I no longer have a selenium recifier it has been changed to a large diode...Further if i compare the photos on the german saba discussion forum, the wirings in the radio have been altered and because of my inexperience I have not figured out exactly what is going on with it all......The double 50uf smoothing cap I changed to a 47uf F and T equivalent....I have added some x2 and y2 0.01uf suppression caps across the relevent cables and it has done nothing to reduce the hum....it has however removed any sibilance ( i.e when I hear "S" or "SS" or "ASE" in narration they are no longer drawn out to "SSSSSSSS")
I have added a new ech81 again "no joy" but I have noticed that the new valve had a very shiny mesh anode and the bottom of the mesh has darkened after a few hours use.....there is nothing wrong with the original valve : they sound the same to my ear.

With the volume/tone controls I have squirted cleaner in them and if I play around with them or tap them it does not affect hum....The hum is definately at low/comfortable volume or no volume...
I have a few valves coming in the post...just to make sure...is it safe to remove the ecl 82 output valve and turn on to listen for hum?
Basically the radio is working and tuning great on all band widths its just this hum....I can only compare it to my cd valve output stage which is unfair because I spent hours and hours reading and planning to make sure there was none.....I have heard in the past a rodger cadet amplifier which was valved and it did not hum like this at all....I am sure its not right
The only electrolytic left in here which is original is the 10uf speaker cross over capacitor...have ordered a replacement.

[Steve_P]

If it's got a mains transformer, the valve heaters are wired in parallel. So pulling one out to see if it hums still is a good idea.

Modern smoothing capacitors are made to preferred values.Replacing 50uF with 47uF is fine.

The other thing is that with a mains transformer, you may need to replace it with what is called a 'Bridge Rectifier', i.e. Full Wave rather than Half Wave. This could cause the hum. Has anyone got the circuit for this set so we can check this first.

Cheers,

Steve P.

[chokesrule]

Hi,Steve, i am waiting for the circuit diagram to be emailed to me , it should come in the next few days.....something is not right with how its been re wired it does not tally with the pictures on the german saba site

http://saba.magnetofon.de/showtopic....3408&pagenum=2

you have to scroll down to the pictures.....


In the picture one of the seconday windings is connected to a tag post near the front of the double smoothing cap....it is not like that on mine.....going have to get a camera from somewhere to show....definately need the circuit diagram....

[chokesrule]

http://www.saba.magnetofon.de/showto...3408&pagenum=2

[howard]

Hello Chokesrule,

I think this is the right page .....

http://saba.magnetofon.de/showtopic....ight=villingen

If you send your email address via a PM I will send you the service sheet for the Villingen 125 tomorrow.

Howard

[DAVEHALL]

Originally Posted by Steve_P

Dave - try looking at this thread: https://www.vintage-radio.net/forum/...ead.php?t=7469



Explains it better than I could.

Cheers,

Steve P.

Steve - thanks - my inroads onto radio/electronics in those days were as an ignorant hoper/poker .

[Geoff 555]

Hello I am not sure how relevant this is but I had a radio (AC only) that had a persistent hum that despite recapping etc. would not go away. When I cleaned the volume control I noticed that the mains contacts were very very close to the volume control track, under 1/8" away and thought that maybe it was picking up mains hum, swapping the live and neutral leads so that neutral was switched cured it completely. Just a thought.
Cheers.
Geoff.
Could not change the control to double pole switching ,it was a special and unobtainable.

[chokesrule]

Hi, I have thanks to Howard's circuit diagram, changed the vintage diode to a modern diode. put a snubber across it.I also added a 22ohm resistor so the set is running on 220v. The resistance of the vintage diode is basically identical to the modern diode. My small electronic knowledge leads me to assume the set had been running on too high a voltage (shown on circuit diagram). I cannot be sure of this statement as I did not measure the HT voltage through the vintage diode :I am only assuming. This has not solved the HUM.
I pulled out the output valve: HUM still there. I have also noticed the hum is present instantly at switch on, before the valves had time to warm. I have downloaded a signal generator program and have found with horror that the radio is not the only faulty equipment here!! I am struggling to make my mind up whether it is 50hz or 100 hz, I have sat for an hour switching signals and have come to the conclusion my ears must be on their way out as I just cannot make my mind up...I have even tried singing 50hz /100hz...
So will now try and find a thin piece of aluminium to shield the output transformer from the mains transformer and see what happens there...Thanks for all this help Alan

[Herald1360]

Originally Posted by chokesrule

So will now try and find a thin piece of aluminium to shield the output transformer from the mains transformer and see what happens there...Thanks for all this help Alan

Not aluminium, iron or steel and the thicker the better if it's magnetic shielding you're after.

[Jonster]

You could try changing the orientation of the output transformer around and see if that makes any difference?

[Billy T]

Originally Posted by Geoff 555

swapping the live and neutral leads so that neutral was switched cured it completely. Just a thought. Cheers. Geoff.

Just a thought, yes, but a very ill-advised thought. Swapping live and neutral is a very dangerous thing to do Geoff, it means that the mains connected circuity of the radio is live at all times even when the switch is off. You may know that, and take suitable precautions, but some day/one day that could kill an unwary user. Not to mention that switching the neutral on its own is probably illegal, it certainly is under most enlghtened administrations.

You would be better to fit a line switch in the supply cable, or forgo originality and fit an alternative control, there is bound to be a suitable substitute, but whatever you do, for safety's sake, switch the active conductor. It isn't worth injuring or killing somebody for the sake of notional originality.

Cheers

Billy

[kalee20]

Originally Posted by Herald1360

Not aluminium, iron or steel and the thicker the better if it's magnetic shielding you're after.

Aluminium or copper will work as a magnetic shield, if thick enough (just think of IF transformers). It needs to be thicker than the skin depth at the frequencies of interest - so 50Hz would need about a 10mm thick copper shield. Not really practical I agree - but not impossible.

I see that chokesrule is in Devon - so am I - if that is North Devon then I'd be happy to drop round at a mutually convenient time. If that's of interest, send me a PM.

[Billy T]

Aluminium or copper will work as a magnetic shield, if thick enough (just think of IF transformers). It needs to be thicker than the skin depth at the frequencies of interest - so 50Hz would need about a 10mm thick copper shield.

Aluminium or copper have zero shielding effect on low frequency or static electromagnetic fields. They 'shield' via induced eddy currents which cause 'opposing field' losses, which is an entirely different mechanism. Try it with a permanent magnet and you will see that the field strength is the same on the other side of 1cm of copper or aluminium as it is in free space.

The only effective means of shielding magnetic fields is via ferrous metal, which can contain or divert the magnetic lines of force. As I mentioned in a recent thread with a similar issue, if you cut the top and bottom out of a tin can, flatten it then insert it by hand between the power transformer and the output transformer (close to the output transformer but not touching it) this will either reduce the hum slightly if induction is the cause, or have no effect. You do not have to ground it in any way, but I'd put a flying lead to ground from it if there are any live terminals around that you might touch.

If the laminations of both transformers are parallel and closer than 5-6 cm then coupling is possible, but if they are at right-angles to each other or further apart then it is quite unlikely.

My business is largely dedicated to EMF effects and EM interference, and I would never use copper or aluminium of any thickness as a primary shield. I have used a ferrous/aluminium/ferrous sandwich in a single-plane shield for a large distribution transformer in a shopping mall but the aluminium was for eddy current losses only in order to enhance the efficiency, otherwise we would have needed much thicker steel, and it needed a crane to install it as it was.

If the radio is original in respect of the output transformer placement then coupling is also unlikely as the manufacturer would have had to sort it during production.

Cheers

Billy

[kalee20]

Originally Posted by Billy T

Aluminium or copper have zero shielding effect on low frequency or static electromagnetic fields. They 'shield' via induced eddy currents which cause 'opposing field' losses, which is an entirely different mechanism. Try it with a permanent magnet and you will see that the field strength is the same on the other side of 1cm of copper or aluminium as it is in free space.

Static fields, yes, completely ineffective - but not AC fields.

Putting 1cm copper plate around a permanent magnet will have no effect on its field strength, I agree. But put the plate around a 50Hz energised electromagnet, and the field strength will be diminished onthe other side of the plate.

The shielding effect is, as you say - due to induced eddy currents which oppose (by Lenz's law) the inducing field. As frequency drops it becomes of less and less practical value - 2mm of soft iron or mumetal versus 10mm of copper for 50Hz is a no-brainer (and it will be more efficient, I agree again). But that's not to say copper or aluminium is completely ineffective! A superconductor would, in theory, work right down to DC.

The point about the manufacturer will have positioned the transformers so that hum isn't a nuisance, is what we'd all hope. But my Ferguson 373RG, which has its original transformers - hums gently (not intrusively) from the loudspeaker at all times from switch-on, even with all valves removed, and I conclude it's stray magnetic coupling. So manufacturers aren't always blameless...

[Geoff 555]

Hello Billy thank you so much for your warning, I may have made a mistake in doing that but as the radio has a mains transformer, I really should have mentioned that I guess, I thought that it would be OK. It was originally wired like that (switched neutral.) and I though that I was being clever and switched the live lead and the hum was terrible.
I dont wish to drift OT but would removing the mains from the volume control and using the wall switch be a better idea?
Thank you again.
Cheers.
Geoff.

[kalee20]

In a word - yes.

It's also a good idea because it'll save wear on the volume control's track - which otherwise gets a little of its life used up each time it is switched on or off.

Bringing 240V of mains right up to the signal wiring isn't really the right thing to do for low hum, although usually it can be got away with.

It's still baffling how a humming radio left the factory, unless the volume / on/off switch has been replaced.

[f.cooper]

Hi,
You never answered the question properly about where the hum is coming from but you did say that the hum was still there with the output valve removed. With this valve removed it is very doubtful whether anything at all could be heard through the loudspeaker. It makes me think that either you have a noisey mains transformer or that your ears may be more sensitive than most. Listening to a cd is not a fair test as with a modern system the background noise would be rather low anyway.
By the way listen very carefully to almost any mains transformer and you will hear a very slight hum when mains power is applied.

[Herald1360]

Originally Posted by kalee20

A superconductor would, in theory, work right down to DC..

Not just in theory.... you can float a small magnet quite happily above a chunk of HTS in a saucer of liquid nitrogen until the LN2 evaporates and the HTS warms up.

http://www.sci-museum.kita.osaka.jp/...erconduct.html