You may want to check at http://www.oldradioparts.com/. They have listed a used 95-418 transformer for a Zenith 7-S-204. I compared the 204 diagram and your 229 diagram and both have identical power supplies. Your radio uses a 95-415 transformer. The tube lineup of both radios is the same except the 204 has a 6T5 eye tube. The 95-418 transformer HV winding is 335-0-335 volts and probably the one in your radio is the same. The 6 volt winding of the 95-418 would probably have a higher current rating because of the extra tube. Other sources for new transformers are tubesandmore.com and radiodaze.com.
Radiodoc
My post was not clear, as I was not sure what I was trying to ask.
I got lucky and found a used replacement at John Kendall’s Vintage Electronics at
http://www.vintage-electronics.com/rjy.htm
I am new with this hobby, however I wanted to see if I could work backwards and possibly calculate the B+ supply voltage, here is what I did.
1. Looking up the plate current on the 6F6 Power tube the RCA tube manual indicated for zero-signal plate current of 34ma @ 250V, for maximum signal plate current would be 36ma @ 250V. I took the difference and used 35ma.
2. Speaker coil per the schematic is 1250 ohms measuring the speaker transformer the value was 696 ohms.
3. According to the socket voltage chart the plate voltage on the 6F6 power tube is 247V and all voltage reading are to chassis ground.
4. Looking at the schematic I found three resistors in series with the B+ center tap to ground. 300 ohm, 27 ohm and 125 ohm.
5. I also saw C16 and C17, I know what they are for but I don’t know what the impact is on the final B+ voltage so I discounted them for now.
6. Resistance sum of 6F6 plate circuit is 1250+696+300+27+125= 2,398 ohms.
7. Using a 330-0-330 transformer the voltage drop across the total resistance in the circuit would have to be 83 volts in order for 247 volts to be present on the 6F6 plate.
8. Using ohm’s law I divided 83 volts with plate current of 35ma and came up with 2,371 ohms. The total circuit resistance of 2,398 ohms came very close to the calculated value so it appears the radio was designed for a 330-0-330 power transformer.
I am not sure if my approach is correct, I should get the transformer in tomorrow to test the theory.
I discovered the speaker coil measured low about 1023 instead of 1250 ohms. When replacing both electrolytic I discovered the originals were replaced with 40mfd, I am just wondering if the larger value capacitors caused the burning of the power transformer and possibly could have caused shorting in the speaker coil winding.
Larry
Larry,
That's pretty close to what I came up with. I was looking at the 229 schematic along with some others in the same Beitmans book and came across the 204 that had the same power supply. I decided the 204 had a transformer with a different number because of the extra tube but probably work. The 40 MFD caps seemed a little excessive. I probably would have replaced them with a couple of 20MFD or at least a 20 and a 10. A lot of the radios I have with dynamic speakers have the field coil rated at a certain resistance hot. After I have restored a radio, I use an AC amp meter and measure the operating current with the radio operating and add a fuse to the radio generally under the chassis. I allow a little for initial surge at turn on. Transformers can be quite expensive these days. Good luck with your set.
Radiodoc
As I understand the speaker coil will show a low value until the coil is at operating temperature. This makes me feel better knowing I may not have to replace the speaker. I am currently rewiring the set, but as soon as I can power up I will check the current on the coil.
Thanks again Larry
Anyway, 40 MFD is quite acceptable. I think that 30 is more agreeable. 20 and 16 are fine, though hum may be louder. It certainly won't be too loud, as sets of this type often came with such low value condensers. Values of 30 to 40 MFD are better with filamentary rectifiers like the 5Y3, as these cool down almost immediately, and are less likely to overload. Unless a power supply of this type was originally designed for high vale condensers (over 40 or 50), though, don't put them in. My DeWald television has a power supply which is designed for high loads. It has two 5U4 tubes in parallel, and has primary electrolytics that total 80 MFD or more.
One thing you might also want to check for is a short between the field coil and the frame of the speaker, that is, if the speaker comes in contact with the chassis. I don't know of too many field coils which increase or decrease by over 200 ohms as they warm up or cool down. That's kind of excessive, though possible, I guess. If the speaker does not come in contact with the radio chassis, the field coil is not likely a concern of yours even if it is shorted to the frame. Lacking 200 ohms isn't going to affect radio performance much. If the field is shorted to the frame, just don't touch the speaker and the chassis at the same time. I have never had a speaker in which the field shorted to the frame, but it is always a possibility. I have had speakers with slightly shorted field coils. The field coils function normally anyway.
Thomas
It is possible the speaker had been replaced sometime or the other. This could be a possible reason for a much lower resistance of the speaker field coil.
Radiodoc
The peak voltage out of 300-0-300V (rms) xfmr is 300 x 1.414 = 424V. On the other hand, there will be a drop through the rectifier tube and some ripple that will cut the B+.
330 x 1.414 = 467V