Marc, Thanks for another tidbit of info.

I totally agree, If you understand how it works you can understand why it doesn't. That's been pretty much my mantra through my (past) working career as an engineer.

I hadn't picked up the earthed shield on the transformer, I looked at the 11-81 circuit as well. I assume it's to further minimise eddies in the core or EMF? How did you determine the AC voltage on the chassis, what do you compare it with? Does it affect the secondary AC output measurements when compared to chassis?

I guess the RCD would not detect the voltage on the chassis as it is induced from the transformer and not upsetting the balance of the primary input.

Thanks, David

David, I finished it this afternoon, all I have to do is make the plastic dial cover, perhaps if you could give me the details on how you did yours again ?
I'll be posting photos to Brad in the Cabinet repair section. The purist won't like it as I've had to repaint it, but I don't care, it gave me a lot of satisfaction.

Shield I believe is more to do with interference. being what it is it will act as a turn. A short to ground on the secondary will not trip RCD's.

I repaired a set recently where a shorted OP tube resulted in the transformer smoking & its a wonder, as I have said, that it did not start a fire. Similarly at the Men's Shed, a donated "Stick" welder burnt out the earth wire when its transformer went to ground secondary side.

This is the reason that I will often isolate the transformer secondaries and insulation test all windings to transformer body and winding to winding. I will not power a any set without inspection and a mains set without confirming that the primary side is actually safe: Lots are not.

I have pointed out to the Americans several times, on their forum that on occasions where they have used transformers that the chassis is better off grounded, rather than have line caps to neutral, as the way their 2 pin NEMA plugs work they can be reversed. And a charge will not really be dissipated (In my book) by a line cap as its a resistor to AC. This was the source of hum in one set there.

It is rather simple to determine if there is induced voltage on the chassis where there is no earth wire. A neon tester will tell you if its over fifty volts charge. You will get massive crackling when you touch it with something metal or an instrument probe and in this one the antenna terminal has a neon to ground and a ground separate to the mains. A volt meter on AC, to antenna earth to chassis will read. High impedance will give the best indication.

This sort of capacitive induction between wires also goes on in your house. The CFL's set up a relaxation oscillator. When the induced charge gets to around 30V they fire, discharge the charge and then it starts all over again. Frequency depends on wire length. Incandescent bulbs are a resistor, so that phenomena won't happen.

Rudolf,

I will send you an email about the dial covers. Also I wouldn't worry about the purists, its your radio, it's not rare or so desirable that it needs to be kept original. If I was worried about that all my collection would be in a skip I always think of it barn find classic car, they are restored to new or better and put on show, why not with radios?

Marc, thanks for the info.
That welder sounds dangerous
The Yanks have never been big on earthing. I thought the line caps were for RFI control. You are talking line to line not line to chassis? Their non-polarised plugs fitted on a hot chassis set is asking for trouble.

I have a Kriesler 11-81 here with a two wire line cord, I'll test your chassis measuring method when it gets restored, thanks.

Cheers, David

That welder (which was not the first I have seen do that) went to scrap metal. I have systematically worked my way through every thing in that Mens Shed that is not "fixed wiring": It's scary.

It has gotten to the point where absolutely everything that comes in the door be it mechanical, electrical, or chemical, is quarantined.

Donations "In good faith" like with many charities, can translate into waste dumping. Several items have been lethal, or broken to the point of dangerous.

If the heater & mains wiring is good (should be) one can pull the rectifier which will stop it generating "B" voltage. That figure eight wire can get cuts in it. Check it carefully.

I love the genius that put a second hole in the chassis for a three wire cable grommet beside the other smaller one. It would have been a wonderful idea to put a corresponding hole in the rear cover to actually allow a cable in that hole to exit???

Check the speaker, for some reason a fibre grommet on this one was broken? Interesting as this one is as far as I can see: factory.

Thanks Marc,

I've printed your comments and put them with the radio with a few notes, I'll be sure to check them when I open it up.

Cheers, David