Now connect A to C and measure the voltage between B and D. In my example rated voltages might be 2 x 12V and 8V. Those are unloaded voltages, and especially for toroidal transformers those may be much higher than the rated voltage. Measure the AC voltages of A-B, C-D and E-F. To find the polarity you'll have the connect the primary to the mains. Let's say you can find windings A-B, C-D and E-F this way. If you measure mega-ohms your measuring on two isolated windings. Depending on the transformer's rating you'll measure a few hundred ohms between begin and end of a winding. To find start and end of a winding you measure resistance with your multimeter. For the secondaries I presume they're separated. As for replacements pretty much any push pull output transformer should work, except if it's for 41/6K6 tubes, the primary impedances are pretty close between 45s, 47s, 42s/6F6s, 6V6s, 6L6s, and 6BQ5s, it isn't that critical.The primary's wire is thinner and as W5VO says has a higher resistance. The existing transformer could also be miswired, the B+ should always go to the center tap of the primary, so it's worth disconnecting and rechecking. Other threads lead me to believe it will work in this context. I'm looking at the Hammond 125C as a replacement for this transformer. Does anyone have any info on which is primary/secondary and start/finish/center tap? One side has a black center wire, the other is red (or orange?). There are 2 end connection lugs on each side with center wires also on each side. Checking continuity between leads shows pretty much everything open. The transformer is a Jefferson Electric 2766J but I have no info on its wiring layout. I'm convinced that the wiring is not correct and also that the output transformer is bad.
Lack of plate voltage to the first 45 (the second 45 is getting 243V at the plate) led me to look at the speaker output transformer wiring. I was not impressed with the quality of the previous work. It was recapped but not working when I received it. (03-02-2016, 02:52 AM)rrova Wrote: I'm working on restoring a Philco Model 90 (2 45's for output, Min-max switch, March 1931).
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