Testing a Radiola Grand radio today found that the 3 transformers all have good primaries, but open secondaries. The secondaries on the last 2 transformers are center-tapped, and I get an open circuit on both halves of the windings. It seems strange that ALL the transformers have bad secondaries, but that's the way it is. This is a very original looking radio and in excellent condition, so I definitely want to keep the chassis looking original too with the original style transformers.

So, what's the best way to get this working?
Does anyone repair these transformers?
Or, does anyone have some of these in their spare parts, or on a junker chassis?
Or, does anyone know if these same transformers are used on any other easier-to-find RCA products?
The solution might be to hide a tiny resistor and capacitors by the transformers to capacitively couple the stages, so does anyone know what the resistance of the secondaries should be?

Thanks!

I think this is a recomended one,http://www.radiodaze.com/category/256.aspx. Seems to be a common problem.

Thanks for the suggestion, but I'd rather leave this rare radio non-functional than replace the audios with modern parts that don't look anything like the originals. These modern parts might be acceptable if the original transformers had outer shells that the new part could be hidden inside of, but they don't.

Hammond also makes the coil bobbin without the iron, so you can take apart your transformers and use the old iron, though it will still look new.

Another possibility is to "zap" the windings. The chance of success is slim, but conecting a high voltage (600-800V) low current source to the windings from say, a capacitor tester briefly, may arc the breaks in the windings and fuse the breaks together.

The problems with these old transformers is the acids in the paper, mixed with moisture causes the ultra-fine copper wire windings to corrode apart. Not much else you can do, but the zapping method has a small chance.

-Steve

I wouldn't touch them. You can clip in some temporary replacements to see how the set works.

I have tried the "zap" method using a charged eletrolytic capacitor, with some success. Be CAREFUL when doing this!!

I used this method on an early 1930s output transformer; after zapping the winding back to continuity, I cooked the transformer winding for an hour or two on a low-voltage power supply, in an effort to stabilize the weld.

If you are using a DVM to measure the winding, BE CAREFUL! I have been fooled several times into thinking a transformer or field coil was open, BUT IT WAS NOT! I was using the DVM in autoranging mode. I would suggest you test using MANUAL mode (you select the range), and cycle through the ranges before writing off the transformers.

"Zapping" may work, but it probably does so by creating a carbonized path around the broken ends, not by welding.

I would agree with Alan. Just leave it alone. If you're dead-set on getting the radio working again, you might want to check with Sonny Clutter (radiolaguy.com). He's restored quite a few RCA radios that use these early Westinghouse transformers. I think he has someone repair/re-wind them for him. The #1 transformer (far right side, next to the grid-leak cartridge) is similar or the same as the transformer used in the RCA DA detector amp, the Radiola RS, the Aeriola Sr. amp and the Radiola AC amp. The two transformers with center-tapped secondaries are a different story. I'm not sure they were used in any radio other than the Radiola Grand. You might get lucky and track down the former, but chances of a good Westinghouse transformer with a center-tapped secondary turning up loose are slim.

No, I am using an old-fashioned meter with a needle because it's lots easier to see an intermittent connection by watching for the needle to jump than to watch a digital readout. It's actually pretty rare (like never) that I use my DVM with any old radio work. I guess I don't see any harm to trying the zapping method, but will be really lucky if this works on all 3 transformers.

this has some good illustrations http://radiolaville.com/graphics/docs/R ... 0Grand.pdf
looks like a good cause to rewind. cant break broken. may as well give it a shot. make sure that it doesnt work first

Although I have not done this repair on the RCA transformer you mention, what I have done in the past is bypass the secondary with a small cap (.005u-.01u) and small resistor (1/4w 100K), typically does the job. Connect one end of the cap to the plate side of the primary and the other through the resistor to ground, taking the secondary lead to the next stage grid from between the cap and resistor. Be sure to disconnect the secondary. Today, you can probably find a small tantalum cap and 1/8w resistor which will tuck into the transformer case or some other unobtrusive area where it won't be noticed. Alternatively, if cash is no object, and you're looking to rewind, some years ago I had Hammond mfg. custom rewind a transformer. I don't know if they will still do this, it was expensive then and I'd hate to ask how much now but...

I have had success in Zapping transformers about 1 out of 3 times. In some cases, there appeared to be success initially, but the transformer failed later (likely the "success" was nothing more than a carbon track, as suggested by Alan Douglass). But I use a NEON SIGN TRANFORMER for zapping. It puts out 6KV at a low current. It will jump about a 3/4" arc. I only do it momentarily (and carefully, of course). I suspect that this method may indeed weld the wire between adjacent layers.

IMHO, if I owned such a valuable radio, I would pay to have the transformers rewound, as long as their external appearance would not be altered. One company often mentioned in this forum is Heyboer Transformer http://www.heyboertransformers.com/. The alternative is to simply leave it alone - after all, it would likely NOT be a daily driver! But I am always curious as to the performance of these unique old sets.

you wont get the same performance using a capacitor as you would the original equipment design transformer. at least it didnt work well in a superhet GE that I tried that with. replacing the IF transformer improved performance considerably

Granted, I really don't know whether or not a carbon track or a weld is made with the zapping method. Nor is it guaranteed to last.
Though, what is it gonna hurt if the winding is open?

I once was successful on zapping a winding in a potted flyback transformer in a recent made RCA projection TV. (It was one with a CTC169 chassis) I determined one of the secondary voltage supply windings was open, which supplied vertical deflection.

A new one was ordered, but when arrived and installed, the set was dead. We ordered a second one, and it was not any better.
The owner of the shop refused to believe we had two brand new defective transformers, and insisted there is something else wrong.

Believing I was correct, I zapped the defective winding and got continuity!
Once installed, the original "zapped" transformer worked perfectly!

...and convinced my boss that we did indeed get two defective new transformers.

The parts distributor was called, and soon it was revealed that there was a run of bad transformers and they were being recalled.
The transformer was on backorder for a significant time, so we made the proposal to the customer that he could either wait, or try using the TV with the "zapped" transformer until the new one arrived.

You know, the darned thing actually did the job! Who knows how long it would have lasted?

Anyhow, sometimes, you gotta do weird things to make things work.

-Steve

I would not expect RC coupling to work too well in a tuned circuit like an IF stage.
However, in an audio stage like this, it could work well enough and would be one of the cheapest repair options out there.

More on RC coupling, and before doing any zapping.

To be clear the transformers involved are audio frequency so RC coupling should work; again, I've done this in the past with success. However, I took a look at the Radiola Grand schematic (there's a good link to it in this discussion string) to find that the final audio output stage is a push-pull setup, hence the two center tapped transformers. Just a note, the final one of them, the one that couples the output to the speaker, is a center tapped primary - not a center tapped secondary.

RC coupling may still work for you, but may not be fully implementable as the push-pull arrangement requires a phase inversion to the second power-amp (PA) tube. You should check carefully if both sides of the center tapped secondary of the PA input (driver) transformer are open or if just one side is open. Do the same with the primary of the output transformer. RC coupling can be used to fix one side but not both as it can't be used to invert the phase. If you find that you have one good side secondary of the PA driver transformer, then its actually possible to get the set working without RC coupling the driver, by only using one of the two push-pull PA tubes, but the result will be somewhat lower volume. If you choose to, you can RC couple the open phase to drive the other push-pull PA tube, provide the primary of the final output transformer is good. If it turns out that both sides of the driver secondary are open then you'll only be able to use RC coupling to operate one side of the PA tubes only, again volume will be somewhat lower.

Thats probably a lot for one post but, I would avoid doing any "zapping" until its certain what is open and whats not and you've determined whether or not rewinding is an option for you. Feel free to contact me should you want to discuss further. Best of luck with your project.

Azenithnut mentioned the Hammond core. That is what I use on Radiola type audios with steel that has a 1/2 inch window. It is available from Radiodaze and costs about $16.00.

http://www.hammondmfg.com/pdf/124C.pdf

It has a center tapped secondary and is not too expensive. The core fits on the original steel inside the original case and looks appropriate.

Here is another option.

http://www.hammondmfg.com/radiola1.htm

Ed.