philco: 38-3XX

 Hello again, Another newbe question ; I have a 38-3 and a 38-4 Philco. I was wondering if the power transformers are interchangable. The 38-3 is 115v 50 -60 cycle,115-25cycle. the 38 -4 is 110-120v 50 to 60 cycle. 110 V to 120- 25 to 40 cycle, and 115 to 230  50-50 cycle   Thanks in advance George

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The power transformers for a 38-3 and a 38-4 should indeed be quite similar.  The 38-3 appears to have a slightly higher capacity power transformer, based on my observation that the high voltage secondary winding as a little lower resistance as indicated on the schematic.  That would make sense since the 38-3 has one more tube than the 38-4.  Even so, the difference is fairly minor.

Since the 38-3 transformer is a little higher capacity, it is fine to use it in either the 38-3 or 38-4.  Using a 38-4 transformer in a 38-3 might result in a transformer that runs a little hot, although it is well worth trying.  If it runs a bit hot, lowering the AC line voltage with a small bucking transformer can be a good solution.

Since these transformers were designed to run a several frequencies, and 60 Hz is the highest frequency they were designed for, most likely these transformers have some margin built in.  Operating at lower frequencies is generally more stressful on the transformer, so running with today's 60 Hz USA power, it should run cool.

Best regards,

Tom

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Thanks again Tom. I am going to try it. Let you know  how it works. George

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