Hello all.
I have saved an old His Master Voice, Model 508.
it is in amazing condition, I have a small problem, it was missing a few valves so I replaced them, was excited to turn it on, it all lit up and looked good, but no sound and a little smoke, is there anyone in Sydney area that maybe able to help me? very keen to get this old girl going.

No no no no!!!

Plugging in an old radio without a few checks can be disasterous. Hopefully the smoke you saw is only a resistor and not the power transformer.

The capacitors used in these old things dont make the distance.
The electrolytic capacitors on the power supply rail usually dry out and go short circuit (or close to it). This puts considerable load on the mains transformer, usually resulting in smoke.

The capacitors used in other parts of the radio were made primarily from paper. These go bad as well, usually not enough to cause a catastrophy but will usually prevent the radio from working.

Welcome to the forum. We will do our best to help you out. There are some rather knowledgeable people here


Ben

Thanks Ben. The capacitor on the speaker is leaking some of its oil also. I put the unit on my PAT tester first to see if there was any sorts and to check the polarity etc.
fingers crossed someone can help.

PAT will only tell you what the primary side of the transformer is doing. All the trouble is on the secondary side.

Fair enough, Do you do Repairs? I go past your way a lot on the way to Urulla and Armidale.

I will confirm the danger of plugging in sets without doing rudimentary checks ,as I fix.

I have had one radio as a guest for several weeks, as the transformer lost its smoke & was rewound.

One of the quick checks to do first, is actually to see if the speaker works. Some radio's are notorious for wiping out speaker transformers and the decoupling cap often across the primary of the OP transformer, has the highest fail rate.

Striking a 9V battery across the primary of the OP transformer is the quick test.

A PAT tester is useless on an electrolytic cap (I have one & would not consider it a I have better) Do remember that it puts out 500VDC and can exceed the rating of some caps.

A cap leaking chemical is a bin job. The outside of the wet type is negative and may be in some cases insulated from the chassis. The electrolytic, when left, will lose polarity, often present as a short circuit, and in such circumstances they have been known to explode.

Marc

Thanks for the info Marc,

JD
Yes I do repairs. Certainly not on the scale of what Marc does.

If you want a quick job, then I'm out. Its strictly spare time only as my 'other' radio job takes up a lot of time.

By all means call in sometime, I can at least assess it for you.

My email address should be in my profile.


Ben

Thanks for you help Ben.