I've restored two Philco Model 90s with the single type 47 output tube and now I'm working on one with push pull type 45 output tubes. The former have three-wire speakers with a four pin connector; one pin is not used. The earlier model with the 45s has a four-wire speaker and I have no continuity in one of the speaker pins (not the same pin not used with the later type 47 model 90s). Do I have a problem or is this normal? Since the open pin on my four-wire speaker is not the same open pin on my three-wire speakers, I don't want to simply test my four-wire speaker by plugging it into one of my restored model 90s having the three-wire speakers.
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From looking at the diagram it looks like all of the connections should show some resistance to each other. Bet you got a bad output transformer or field coil.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
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Louis, there should be continuity between all pins. Hold the plug with the pins facing you, start with the small pin. It is connected to one end of the transformer primary. Moving clockwise, the next pin connects to the primary center tap and one end of the field coil. The third pin connects to the other end of the field coil. The last pin connects to the other end of the transformer primary. Which pin is open? If it is the small pin or pin four, the transformer is bad. If it is pin three, the field coil is bad. It could be as simple as a broken wire. The field coil should read about 2700 ohms and the transformer primary should be 200-300 ohms.
Steve
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Steve,
Thank you so much for your advice. I was going to do some wire tracing to see what was open but testing the speaker connector pins as you suggested made it easier. Using your convention; holding the speaker plug facing me, starting with the small pin (as pin #1) and working clockwise, it appears to me that pin #2 only connects to one end of the field coil and pin #3 connects to the primary center tap and the other end of the field coil. Regardless, I have no continuity between pins 1&2 nor do I have any between pins 2&3. Its 150 ohms between pins 3&4 and 150 ohms between pins 1&3. 300 ohms between pins 1&4. This indicates what I feared most has happened; the field coil is open. Not sure what to do about that other than to try and find another speaker. Thanks for your help.
Lou
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Louis, I may have been wrong about the pinout. I didn't have a push pull 90 speaker to look at. All I had to look at was a K-17 from a later model Philco. I just assumed they had the same pinout.
Steve
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One more thing. There are two Philco model 20 speakers on Ebay right now. They will work with your model 90, however they won't sound as well because they have a stiffer spider.
Steve
M R Radios C M Tubes
Steve,
I figured I had little to lose so I did some surgery on the field coil and was lucky enough to find the discontinuity right where the lead-in wire connects to the fine coil wire. Soldered it back together and used a drop or two of Super Glue to hold things in place. Took about 30 minuites from the time I discovered the field coil was open until I made the repair, put things back together, and made some tests. The DC resistance is 3200 ohms; within 20% of what you said it should be. Thanks for your help.
Lou
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