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Leon Crampin · 31st May 2020, 10:46 pm

If you know which winding was connected to the valve heaters, apply 6.3V to it from a suitable transformer, and measure the voltages of the other windings. There will be a small error using the transformer in reverse, but it should give you a good idea of the voltages available. If you have two windings each giving a plausible primary voltage (say 120V), the one with the lower DC resistance is the primary. The core looks good for 50/60 Hz, but a soak test off load will show excessive heating if this is not the case.

Leon.

31st May 2020, 10:46 pm	#8
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,873	Re: How to identify an unknown transformer. If you know which winding was connected to the valve heaters, apply 6.3V to it from a suitable transformer, and measure the voltages of the other windings. There will be a small error using the transformer in reverse, but it should give you a good idea of the voltages available. If you have two windings each giving a plausible primary voltage (say 120V), the one with the lower DC resistance is the primary. The core looks good for 50/60 Hz, but a soak test off load will show excessive heating if this is not the case. Leon.