Request Opinion on This 39-30 Power Transformer
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Good morning. This is my first AC set (and first Philco) though I've reworked several AC/DC sets of various makes.
This power transformer read 65-70 MegaOhms resistance across the primary inside the set, even when measuring on two nicks I made on those wires to get a direct measurement. With it out of its laminations, I'm reading Infinity across the primary.
It's a bit sooty looking and smells like old axle grease but not really a burnt smell.
I can see some of the winding wire, and there was a silver-dollar size pool of wax on the floor of the cabinet when I got the set. I'm not sure how much wax came out of it since I'm unfamiliar with the AC transformers.
There are several nicks in the cloth wiring of the leads but not that bad. From looking at pics that others did of their 39-30 restoration, this is a bit different style transformer than the original, (leads come out the side rather than bottom center) and probably a bit newer.
The photos are on PhotoBucket:
http://s827.photobucket.com/albums/zz199...ansformer/
If it's not salvageable, I'd like to find a replacement. The Philco part number of the original is 32-7976.
Any opinions are welcome.
Regards,
Clarence
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State, Province, Country: Indiana
The original 1939 Philco power transformers had rubber-covered leads, and may have had high failure rates since Philco switched back to cloth-covered leads in their 1940 power transformers - and did not use rubber-covered leads again in power transformers. (They did use plastic insulation after the war.)
That said, original 1939 Philco sets are found with their original power transformers these days, and the rubber insulation is usually a melted mess. Sometimes you get lucky, and the transformer is still good - as long as you remove all of the old insulation and re-insulate with color-coded heat shrink tubing before applying power.
But all of this does not apply to your situation; I mention all of this for informational purposes only.
I can't really tell from your photos, but yours really does look rather deep-fried.
All that said, I might have a suitable transformer from a 1940 or 1941 Philco chassis. I would have to look and see - as long as you don't mind a slightly newer transformer with cloth-covered wires.
--
Ron Ramirez
Ferdinand IN
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Ron, I sure don't mind a slightly newer one, as long as it fits and functions. I'm reworking this set for myself, and to bring it back to life (I get great satisfaction from getting an old radio working right again).
I'm doing a functional restoration anyway, hiding new components (caps, resistors) under the chassis but keeping the upper part and cabinet as close to stock-appearing as possible. So a variation on the part is not a big deal for me.
Not knocking those who do a full restoration, even those who do museum-quality restorations using only vintage parts of precisely the correct year and serial number series; but I want my sets to function for the long haul without more re-work, so I compromise with the newer hidden parts. I do use tinned wire as close to original appearance as possible.
I am, however, going to try my hand at pre-stuffing my jars of old paper caps, so I can have some on hand for my next set. I wouldn't want to stop in the middle to stuff them as I take them out, but if I had similar vintage ones ready, it would be easy to use original-appearing new caps.
This set will also be my first experience re-stuffing a Bakelite cap. I'm awaiting a Forum answer on its wiring configuration.
Your help is certainly appreciated.
Regards,
Clarence
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Interesting, by the pictures you show the leads to the transformer look like they are cloth covered. It also looks like a 25 cycle transformer judging by the amount of iron used in the core. If it was a 25 cycle transformer something must have really gone wrong in that set to burn it up. The good news is that these sets use 6.3 volt tubes so finding a replacement shouldn't be too difficult, there were literally dozens of makes and models of radios that used a similar power supply layout from the late 1930s up until the 1960s, find a junk chassis from a set that used a 6X4, an 84, or a 6X5 using the same number of tubes with similar current demands, ones using a 6K6, 41, or a 6AQ5 as an output tube.
Regards
Arran
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Much appreciated, Arran. I'll ask around at the local radio club here (TARPA) and with the club I was in before moving (MAARC).
When I got the set, it had a 6X5 installed using a 6-pin to 5-pin adapter, so they at least had problems with the original 84 tube. But I didn't find any burnt wiring or resistors. The dial lamp wire crumbled in my hands--couldn't even rebuild the socket (had to replace with one of my spare '51 Studebaker instrument lamp sockets) but the lamp wiring didn't look burnt. So I don't know the cause of the transformer going bad.
Regards,
Clarence
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Whatever you do, don't use a 6X5. 6X5GT might be OK, but you'd probably be better off with couple of silicon diodes like 1N4007's which can be had for pennies, plus a dropping resistor to tame the B+. Recap and add a fuse. You will not want to repeat the transformer replacement.
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codefox1 Wrote:Whatever you do, don't use a 6X5. 6X5GT might be OK, but you'd probably be better off with couple of silicon diodes like 1N4007's which can be had for pennies, plus a dropping resistor to tame the B+. Recap and add a fuse. You will not want to repeat the transformer replacement.
I received an NOS 6Z4/84 tube I will use. The old one actually was a 6X5/GT/G according to its markings. I don't see a reason to vary from the original parts list. The new 84 tested good on my tube tester.
Regards,
Clarence
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My power transformer was bad, and I had trouble finding a replacement by the Philco part number.
But I determined the specs and found a cross-match in one a fellow radio club member gave me.
I verified the specs through testing that transformer's resistance and voltage readings:
It is an RCA part with number 970445-1 printed on the case.
It matched the voltages of the Philco 32-7976 at 250-0-250 and 6.3v, and
even the bolt holes lined up without chassis modification.
Perhaps someone else wanting a transformer for a Philco 39-30 will find
this cross-match useful.
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Glad you found a substitute. I apologize, I've been so busy fixing bugs in the new Phorum that I forgot to go look and see if I had something.
--
Ron Ramirez
Ferdinand IN
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I understand, Ron. I saw the down time when the Phorum was being re-done.
With the replaced power supply, it came to life right away, got good stations, and all the resistance and voltage checks came in well within tolerance. I've not yet put the push-button assembly back in, and I need to order a dial cover and replacement push-buttons for it. And do some very light cosmetic clean-up to hide some scratches.
Many thanks to you and to all who helped me work through that project.
Regards,
Clarence
(03-10-2012, 08:05 AM)Ron Ramirez Wrote: Glad you found a substitute. I apologize, I've been so busy fixing bugs in the new Phorum that I forgot to go look and see if I had something.
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