The good news is I found a Philco 40-180 (Riders 12-23) at an auction yesterday. The bad news is that one primary leg of the output transformer is burned up. The radio has two 41 output tubes, each receiving plate voltage from a separate leg on the primary of the output transformer. If I rewired so that the good half of the winding was carrying both tubes I assume its likely that the other side will burn out as well. Any thoughts on a potential repair for a radio that won't be played much? Thanks.

Brad, this is your schematic: http://www.nostalgiaair.org/PagesByModel/336/M0013336.pdf

This is a push-pull audio ckt, but it is a rather unorthodox design. Rather than use an inverter tube to drive one of the two p-p 41 output tubes, Philco "cheated," left out the inverter, and drove the bottom tube from the screen of the top tube through a 0.01uF cap. Ingenious but rather inelegant.

As a result, things are rather unbalanced in the ckt. Note, for example, that the output xfmr primary is not tapped at the center.

You should replace the output xfmr. I would try to get by with a center-tapped xfmr, perhaps AES Cat. No. P-T291 ($16.75). You also could check with Gary at PTOP and see if he might have the real McCoy: http://www.oldradioparts.com/

Otherwise, you could try to rig the set to play from just the top 41 tube through the primary winding that is OK.

Doug

Thanks so much for the insight. I will look around for a new output xfmr first.

Brad

I believe that I misspoke about the output xfmr windings. The difference is winding resistance between the two primary windings is probably due to one winding being on top of the other, and therefore a longer length.

I think a center-tapped audio output xfmr should be fine.

Center tapped is fine. My Crosley 1117 uses this push-pull system, and it works extremely well. The transformer is a conventional push-pull transformer. I also converted a phonograph of mine to this system. It only had one unused hole on the chassis, which meant that I could only add one more tube. The circuit works perfectly, and this phonograph couldn't sound any better.

Regarding what Brad said about connecting both plates to one side of the transformer, well, they are out of phase with eachother, and so the audio would cancel. It wouldn't sound very good. You could parallel the tubes so that their control grids both receive their signal from the same point (the point which feeds the 1st #41 tube). I don't recommend this, though. First, putting both plates on one winding will overload the winding. The winding should be half its normal impedance for parallel output if you expect to get adequate power. Push-pull sounds much better, and you should keep your radio that way. The AES transformer will work well.

Hello friend.
Its problem and the one of another friends, they can be solved in an easy way:
Its radio is a push-pull, that is to say, it uses two valves 41 as audio amplificadoras.
The Resistance of Plate of Each 41 is of 1600 Ohms.
Then, we took the double: Value of 3.200 Ohms (it doesn't confuse Impedância Ohmica with Resistência Ohmica).
The Speaker of its radio, I believe, be of 3,2 Ohms or 4 Ohms. Therefore:
NP/NS = Root of ZP/ZS, where:
Np = I Number of Espiras of the Primary
Ns = I Number of Espiras of the Secondary
Zp = Impedance of the Primary
Zs = Impedance of the Secondary.

Substituting:
Zp = 3200
Zs = 3,2; 4,0
Its espiras Relationship between primary and secondary will be the same the Squared Root of 3200/3,2, that is to say, 31,62. If it goes mobile reel of 4,0 he/she gives: 28,8
For each 31 espiras in the primary, you have 1 espira in the secondary. Relationship therefore of 31:1, for mobile reel of 3,2 Ohms and 28,8 espiras for 4,0 Ohms.
In the Practice, you can use another method:
Disassemble the old transformer, how many espiras count you have in the secondary. Don't get scared, they are little. If he/she gives 62, you multiply 62X31 = 1922 (I number of espiras in the primary)
If he/she gives 93 espiras, you will have: 2883 espiras for each primary one. OK?
I hope to have helped!
Any doubts, contact me
Indalécio Alves de Oliveira
its friend in Brazil.
officinadoradio@gmail.com
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