I have the chassis out of my 1936 Silvertone 1970AE, and like to listen to it while I work on the cabinet (and on other radios). However, something started to smell burned, and the smell turned out to be the Silvertone - the power transformer was HOT!!! The playing of the radio did not seem to degrade, but the transformer got hot enough that some sort of wax or tar melted out of the holes that the transformer leads come out through (it has some sort of black metal or Bakelite cover over the windings).

Thank heavens it didn't catch fire, and that the radio still functions, but what could cause it to overheat to such an extent? It had been playing all day long, from about 8:00 this morning to 4:00 this afternoon when I noticed the smell.

The only capacitors that have been replaced have been the power filter electrolytics; all of the mica and paper/foil caps are still there. I don't know if one of those going bad could cause this or not, but none of them look as if they had overheated (no melted wax, except for what ran out of the transformer).

Can somebody please clue me in? I'd hate to have to find a replacement for my power transformer - I doubt one would be easy to find...

Well it could be caused by one of those other remaining old capacitors, but I suspect it might be the transformer itself. It may have developed an internal short.

To find out, remove all the tubes from the radio (make sure you know which ones go where), then plug the radio in and turn it on. If the transformer still gets hot that's bad news meaning you will be looking for a replacement.

Even if it doesn't get hot, the worrisome part would be that you obviously have a transformer that has been seriously over-stressed.

"Something odd I have noticed is when I first power it up, I hear a little snapping underneath, like something is arcing slightly, and the dial lamp flickers slightly, but it goes away and doesn't come back once the set is fully powered up. I can't seem to find the source, though, and nothing smells overheated or feels too hot. Nothing shorted to chassis, either, at least nothing high voltage."

Well, unfortunately I think you may be finding the source of the snapping noise.

I suspect either a HV transformer winding to filament winding short or one side of the transformer AC HV shorted (shorted turns or shorted to case) and the radio was getting by on half wave rectified B+.

Curtis Eickerman

Just freaking great. Looks like I've got a bad transformer. NOW what do I do???? I REALLY like this radio!

I assume that means it got hot?

Any specs. on the transformer with respect to what kind of voltages and currents?

Here is my guess. 250-0-250 (or 500 V Center Tapped) at 150 mA. 6 VAC at ? mA, and 5 VAC at ? mA. If it isn't specified anywhere we could figure out the 6 VAC and 5 VAC based on the tube line-up. Then it is a matter of measuring the physical size to make sure whatever you can get to replace it will fit.

I'm guessing a new transformer will run about $50. Someone around here might have a vintage transformer for less.

Curtis Eickerman

Well, HV measured across the terminals of the 80 tube socket came out to 300 volts or so. Plus a 5-volt secondary and 6.3 volt secondary.

Tube line-up is as follows:

80 (rectifier)
6A7
76
6K7
6C5
75
6F6
6E5 (magic eye - aftermarket add-on)

This TOTALLY sucks...

Before you install your new transformer, replace all the paper bypass capacitors. There is no point in overstressing a nice new transformer from the start.

--Chuck

You need to get real; a 1936 consumer-grade radio has 76 year old parts, and the only thing amazing is that they've lasted this long.

At least it's a replaceable part, and not something obscure like a dial glass.

True. It's just a really annoying setback, is all. I've been enjoying listening to the set - it's easily the most sensitive one I have, reception-wise, and sounds pretty good as well now that I have the speaker repaired and the volume control cleaned up.

Well, HV measured across the terminals of the 80 tube socket came out to 300 volts or so. Plus a 5-volt secondary and 6.3 volt secondary.

Tube line-up is as follows:

80 (rectifier)
6A7
76
6K7
6C5
75
6F6
6E5 (magic eye - aftermarket add-on)

The old transformer measures 2-7/8"W X 3-3/8"L at the laminations, and fits into a 2" x 2-1/2" opening in the chassis.
Hammond has a whole series of tube transformers; just need to know which one I need...

5 V at 2 amps minimum
6.3 V at 2.5 Amps minimum.

A Hammond 373CZ might work if it is the right orientation and size. HV will be a little high to get enough filament current rating. Alternative is take your chances with the 373AZ (smaller). If it is the other type of mounting you have more choices. Here is a web site http://www.hammondmfg.com/300series.htm You can also look at their 200 series (I think they are all the orientation with vertical laminations).

A 372BX might be a good match in the other orientation (X10 case).

I have no idea of price.

You may also be able to find someone who has an exact vintage replacement.

Curtis Eickerman

Curtis recommends the 372BX, I agree but the 272BX is cheaper and smaller as it is just made for USA input voltage of 115 or 125 volts. Use the 125 volt primary tap. (The 300 series is for worldwide voltages)

Output is 600VCT, 5V 2A, 6.3V 3A. This is $59.90 at AES.
New transformers are UL approved and will last longer than used ones.
Don

Don, good point regarding the universal versus standard transformers. The 300 series is expensive (found a price for the 372BX at about $95 through Allied.

Curtis Eickerman

Maybe posting a "WTB" in the classified here would attract a better price offer.

What about a Hammond 273AZ? Would that probably work okay? It's the only one with a "Z6" mounting, which is what I need in order to fit properly.

Did that a short while ago.

The power rating is too low and the price is higher than the 272BX. Can the 272BX fit on the chassis?
Don

Its only rated at 2 A on the 6.3 and you have 2.5 A required by your tubes. It's your call. I suspect it might have enough margin to work especially if you use the 125 V primary tap.

Curtis Eickerman

Hi

Did you try pulling the 80 tube and letting the radio operate? If the transformer doesn't get hot with the 80 removed it's most likely good. Radio circuit is just drawing too much current. Leaky caps?

You could also check AC voltage on each plate of the 80. Voltage should be the same. IF different transformer has shorted turns.

It got hot, all right, with all tubes pulled.

It would probably fit ON the chassis, it just wouldn't mount the same way as the old transformer. As I said, the old transformer would be what Hammond calls a "Z6" mounting.

You could look here for a transformer:

http://www.oldradioparts.com/2a23efl.txt