The Stovebolt Site Forums The Shop Area The Electrical Bay The Radio Bench Power Transformer AD Radio

All,
Two questions with regards to the power transformer in AD radios.
Question #1
Is there anyway to test the power transformer in a AD radio? I am in process of re-wiring and re-capping the radio and noticed that some of the tar has leaked out of the power transformer. I have read a couple posts on this site and other sites where some people have said that this is an indicator that the transformer is shot or may have overheated at one time. My concern is that I don't want to replace all the caps, re-wire only to find out that the transformer is shot and needs to be replaced.

Question #2
I do have a new Merit brand transformer but the colors of the wires do not match the original or the wiring diagram that I have. On the original transformer going to the vibrator is a yellow and black and to the 0Z4 rect is a brown and a green with a red wire going to the ground on the multi can capacitor. On the new transformer is a red and grey for the vibrator and a brown, black/yellow c.t. and green for the 0Z4 rect. Since the colors are different on the new transformer does it matter which wire goes to which pin and to ground on the multi can cap?
Any help would be appreciated.
For those that are interested, I cross ref the GM part number 7255881 to the following replacement transformer. They are Stancor P-4065, Merit P-4076 or Thodarson 22R71.

Thanks Dave

If you isolate the leads on the old transformer, you can take a resistance reading between one of the leads on each winding and ground. The reading should be close to infinite meaning that there should not be a connection. Sometimes the capacitor inside the can starts to short and can generate heat.

For your new replacement, the polarity of the input and output windings is not significant so you need not worry about the color differences.

Fred

Fred,
Thanks for the info. I will check it today.

Dave

My question is, Dave where in the world did you find a replacement transformer??????
DG

I must say I swould not throw away an AD radio because the power transformer is shot. I keep parts radios around for things like that.

One of the other members in another thread mentioned picking up what looked
like an AD radio for ten bucks at a garage sale. Turned out it was an Olds radio. I
got one just like that and for about the same price but it was a 984688 Pontiac
Chieftain radio. Restoring it for use in the original car wouldn’t be worth it but as
a parts radio for an AD rebuild a lot of the parts would be common such as the
tuner internals, coils and that replacement transformer, etc.
I’d grab up any model of these old Delco radios for that kind of money just for the
spare parts.
Denny Graham
Somewhere north of Sandwich, IL

New to the forum, and thanks for the information previously discussed here. I am looking for a 7255811 power transformer or equivalent PN. Mine has and open primary winding and no high voltage. This is for a 1950 Pontiac radio but other models used the same unit.

Stancor P-4065, Merit P-4076 or Thodarson 22R71.

Any ideas or sales offers, thanks

Most of the GM brand chassis around that time used a similar transformer. Personally I have never been able to locate a new transformer by part number but once in a while I will install a used one from one of my parts radios. If you need a used one, you can contact me if you want.

Thanks truckernix, I would like to know what you have used, and how much your asking. What is the best way to get a hold of you?

JP1,
I have sent you a PM.

Polarity on your transformer is not a problem since you have AC current on your secondarys find your primay and it's center tap the the secondarys and it's tap and your set to go, I have NOS transformers for that radio, DELCO's I bought out a UNITED MOTORS radio shop,SORRY they are not for sale, I've made a list of parts interchange parts of GM radios. That power transformer maybe alright, most likely it's been heated up by a bad buffer, give your transformer a chance they are a rugged unit

Denny,
Sorry I have not been on the sight for awhile, been busy working on a VW Beetle for my daughter. I found the replacement transformer with Moyer Electronic Supply Co. They are located in PA, you will have to email them with the PN you are looking for and they usually get back to you in a couple hours. I have also found other parts from a company called Play Things of the Past, they are in OH.


Dave

Can’t remember his name, but Play Things of the Past used to make it to our big
ARCI swap meet here in Elgin. I’ve also been over to their shop while attending
Estes radio auctions in Medina, OH.
Haven’t bought anything from Moyer in a long time. I’ve been away from the
radio bench for several years now, just a few truck radios and that’s it.
Tks for the come back.
Denny Graham
Sandwich, IL