50's car radio repair. Smith and Sons 200X.

[robreddog]

paul...they are all duff !!

[Radio Wrangler]

Transformer burn-up can also be caused by a stalled vibrator... probably allied with too large a fuse. A burned smell is a bit of a give away. That unit needs a good going through of the capacitors and a solid state vibrator replacement as well as the transformer redoing.

Hopefully the head unit won't be such heavy going.

David

[robreddog]

thanks for the replies ,keep them coming, i have opened a whole new learning curve for myself with this radio and have been going through past post's, way over my head, old dog new tricks etc.
has anyone used the royal signals vibrator or any other in a repair, i could use with a re wound xformer.

[PaulR]

You could also think about adding an "Aux" input - see the notes at the top of this section of the forum.

Edit

When I restored one the only source of vibrators I could find were in America so I used the original. That site is interesting - I might suggest that he gets one. I hadn't thought that a stuck one could blow the transformer, but of course it could.

[G6Tanuki]

Many vibrators are - these days - becoming problematic. The chopper-and-solenoid-coil assembly was generally mounted on somewhat-flexible 'leads' from the base, and the top of the assembly was fitted into a kind-of reverse-top-hat thing made of foam-rubber to support it from the outer metal case.

Problem: the foam-rubber was vulcanised using Sulphur. Over the decades as the rubber decayed it released sulphur-dioxide - which combines with any moisture to become sulphuric-acid!

SO2 and H2O ----->>>>> H2SO4

This then attacks the contacts and the coil-winding of the chopper-assembly.

The rubber also crumbles to dust. Any 50+ year old vibrator is likely to be problematic - if the contacts weld themselves in one position it can easily melt the transformer. So don't risk spending money getting the transformer rewound only to cook it again because your vibrator is suffering senile-dementia.

[Herald1360]

Originally Posted by merlinmaxwell

I had a valve car radio when I was about 12 or so, the whole thing was the standard DIN size, I am sure it was all valve.

I believe that some of the last all valve car radios using all glass valves did manage to shoehorn the vibrator supply in with the rest of the set in a dashboard sized unit. Not sure if they were actually DIN sized though!


Found one.....

https://www.radiomuseum.org/r/radiomobil_20x20.html

[TonyDuell]

Originally Posted by G6Tanuki

Problem: the foam-rubber was vulcanised using Sulphur. Over the decades as the rubber decayed it released sulphur-dioxide - which combines with any moisture to become sulphuric-acid!

SO2 and H2O ----->>>>> H2SO4

No it doesn't. It forms sulphurous acid, H_2SO_3. To make sulphuric acid you need sulphur trioxide. You can get that by catalytic oxidation of sulphur dioxide (for example over a platinum catalyst) but it's not easy. I doubt you get it in any significant quantities when the foam rubber decays

Sulphurous acid is a much weaker acid chemically, and while it may well attack bits of the vibrator it shouldn't be as nasty as sulphuric acid.

[robreddog]

I am going to open up the vibrator this morning and have a look, I have been searching for replacement ideas.

[Cobaltblue]

The rubber inside these vibrators is "Sorbo Rubber" has a very distinct smell.

Although it's possible to get these vibrators working and if your keeping this radio for your own use that's a good thing, If I were passing it on to someone else I think I would fit a solid state replacement for long term reliability.

Graham did a great piece of work here:

https://www.vintage-radio.net/forum/...ad.php?t=41944

Hope that helps.

Cheers

Mike T

[robreddog]

hi, Graham...just spent 2hrs going through the post's in the ssv thread (yep know what that means now),that is a hell of a great read !! way over my head.
But understanding improved.
so what to do, build one or buy the one advertised as a straight replacement for the plessey 1214.
Ed, i will be contacting you for the sorting out of the transformer rewind.
getting capacitors and deciding on the vibrator, got a lot on at the moment so may buy one ready to fit.
Rob.

[PaulR]

Personally I would buy a ready made one if the cost isn't too much of an issue. They are fairly expensive but they are ready to go.

[robreddog]

Power unit looks bad only found one capacitor that seems OK and that's the coupler that I would change anyway. Can anyone suggest why the capacitor (I think) is connected from pin 3 (vib) to ground, it's not on my schematic?

The Hunts cap I think is C109.

Moderator should I start another thread for the repair?

[Station X]

No need for a new thread.

[PaulR]

Could it be some sort of interference suppressor? Possibly fitted at a later date?

[Techman]

I've got one of these somewhere. It looks like someone connected yours up to a supply and sat there waiting for it to do something, not realising that you had to hear a 'buzzing' sound, when the magic smoke was suddenly released, probably quite recently, as this tends to be what folk do. I'm guessing you've got the interconnecting cable for the two units, although you don't show it in your pictures - mine is missing, so I was going to have to make something up, hence why it got buried in the "round to it one day, if ever" pile.

I've found some pictures on file from when I last looked at it some four years ago and three of them are posted below for comparison and reference. I think you've got your work cut out with that one of yours (as I will have with mine, no doubt - if I ever bother with it) and it won't be a cheap repair with major components needing replacement/repair. I think there was also an HMV version of the same radio. Lastly, I would strongly advise running it from a bench power supply, preferably current limited - don't use a 12 volt car battery, as there's hundreds of amps available and you may have a flash and a bang if/when something goes wrong!

Anyway, good luck with your quest to fix it...you may spur me on to look at mine again - pictures of the innards of mine for reference to yours below:-

[PaulR]

If you can get hold of one an old desktop PC power supply makes a good 12v (and other voltages) supply

[robreddog]

I have sent off the transformer for rewind, replacement caps and SSV have arrived, I have the connecting cable and my friendly garage owner donated an old 12V battery, so guess I am doing this and will make a start on the power supply when the transformer arrives.

Being a novice at this I was thinking of the best way to test it, would I be correct in thinking I could feed it with an audio signal, with a speaker connected. Much the same as I do through the PU input to a radio.

[Techman]

Originally Posted by robreddog

i was thinking of the best way to test it, would i be correct in thinking i could feed it with an audio signal, with a speaker connected.

The power pack is also the amplifier, as I think you realise anyway, so just connect the 'head' unit to it and see if there's stations being received - once you've serviced the power and amp unit, that is. Your main work will be in that power and amp unit - the radio 'head' part will probably just work as it is, but may well benefit from some capacitor replacement to get it to work better...just try it and see, but not before finishing the main power unit. Obviously a speaker should always be connected when powered up.

I wouldn't use a car battery, it's dangerous, especially if you're a novice! If you must use it then make sure you've got an appropriate fuse in line. The idea of an old computer power supply with the appropriate connections linked out on the multiplug to make it fire up is an excellent idea - as mentioned by PaulR above. I've used an old CB radio power supply in the past for powering this sort of thing, and being 13.8 volts are ideal to replicate a 12 volt battery being charged by a car dynamo, which would be the normal working conditions of the radio, but always ensure there's an in-line fuse regardless. I've used a car battery in the house in the distant past to test large linear amplifiers, but it's not to be recommended!

[PaulR]

A quick ebay search shows many second hand ATX power supplies quite cheaply. Useful for future projects!

[robreddog]

Hi, thanks for the advice, when I say novice I mean at repairing old radios, not in electrical engineering, all the equipment I worked on was battery powered one way or another, up to 200 VDC and plenty of amps as well, so I will be OK using a fused battery supply in my shed. I have a old Leak tuner that I was thinking to use to prove the power supply was good before trying the Smiths radio, does that seem reasonable?