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RE: need help on some un-identified tranny's

24.27.41.140

Triode_Kingdom

In Reply to: RE: need help on some un-identified tranny's posted by Story on July 05, 2024 at 14:05:39

First things first, are you certain the secondary is intended for 8Ω? If so, you might be able to identify the transformer by applying an AC voltage to the primary and measuring the voltage at the secondary. That will give the turns ratio, and theoretically the impedance ratio is the square of the turns ratio. The fly in the ointment is that the transformer will give a different result with the secondary loaded. The ratio will appear greater. It seems that manufacturers through the years have specified their transformers both ways. The ratio you see with the transformer loaded more accurately represents the resistance reflected to the tube(s) in actual operation. However, some manufacturers only use the turns ratio in their numbers, which is simpler for them but not very realistic. This can be confusing when trying to make an identification, particularly if the intended secondary impedance isn't known.

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RE: need help on some un-identified tranny's - Story 16:28:11 07/05/24 (1)
thanks for the guidance, I'll take readings this weekend and see.

The tranny's have only 2 secondary taps besides the ground tap and the tranny's look pretty old so I assume they are 8 and 16 ohm taps. The reading on the other tap is 2.1 ohms.

Thanks TK
- RE: need help on some un-identified tranny's - Triode_Kingdom 17:10:30 07/05/24 (0)
  "The tranny's have only 2 secondary taps besides the ground tap and the tranny's look pretty old so I assume they are 8 and 16 ohm taps."
  
  I don't know if that can be assumed. Just the other day I was looking at an amp online that had 4Ω and 8Ω outputs (don't remember what it was now). It caught my attention because I was thinking horn-loaded woofers (like K-horns) generally present about 16Ω. Also, many guitar amp transformers are designed for a maximum (numerical) load of 8Ω, so they're 4Ω and 8Ω. Maybe the results will be sufficiently unambiguous, but it gets dicey when the secondary isn't certain.

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