Interstage Audio Transformer Recommendations

[dieseljeep]

Originally Posted by polyphase

The DC resistance of a new transformer will be much less than a period original, thanks to modern materials (a good thing). The important parameter, besides current rating, is the input impedance which is 10k Ohms. The 27 specs plate resistance at 9k to 11k Ohms depending on applied voltage, so this is an excellent match

IIRC, I used one of that type transformer in my Wells Gardner chassis model ODM. It was kind of a different design, using some metal tubes and a 76 driving PP 45's, built in late 1935. Naturally, the interstage transformer was open.
I couldn't get enough volume, using the AES transformer, plus the tone control, would have little effect. The schematic is in Rider's seven. The AES transformer is a 3:1 ratio, where the W-G needs a 2:1 ratio.
A 3:1 ratio transformer might work OK in your radio. Everyone I talked to, said a 3:1 was fine.

[MT70B]

Polyphase, Diesieljeep,

Thanks for the additional information. I guess what I was getting at from a backwards perspective was the transformer ratio when I asked about the resistance. Probably making a big assumption that the wire size between primary and secondary are the same. However, the (dissected) transformer in the radio appears to have the same size magnet wire coming out to all of the leads. So using the same backwards logic, the primary resistance is supposed to be 1,600 and the total secondary resistance was 10,600 ohms in the defective transformer. So using the resistance as a loose way to simulate the impedance and plugging the numbers into the turns ratio calculator found here: http://www.maxmcarter.com/classecalcs/tratiocalc.html I get a ratio of @ 2.57 to 1. Since you guys have indicated the suggested replacement is 3 to 1, the primary impedance matches a 27 tube, and the current carrying capability is within range, plus the small size, it sounds like it would be worth a try.

Thanks again for the assistance,

Mike

[MT70B]

Just a note to let anyone following the thread know that I installed the P-T156 interstage audio transformer in place of the defective one in my Amrad Symphony (Model 81) today. So for I have about an hour of playing time with the new transformer installed and it seems to be working quite well. I have plenty of volume and the audio sounds just fine with no distortion detectable by ear. Will let it cook for a while and if all stays well I will install the old transformer's metal cover over top of the replacement, which is small enough to easily fit undetectable under the cover.

Thanks for the recommendations!

Mike