Here's the comparison between the Musical Power Supplies PT275 V2 and the Hammond 270FX. The excitation current of the Hammond was much higher than expected. In both transformers, the excitation starts out pretty linear, then takes off after ~100VAC. Both transformers are edgeing into saturation at high input voltage. I can see now why the Hammond has a rep for buzzing and heating up...
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yes, but it is interesting to find if the 2 curves will ever meet at some point...180 is not too high to cause saturation if testing only for a few minutes or even seconds...when they meet it will mean that the hammonds are using better quality irons...
heating up at idle and buzzing under load are two different things...
heating up at idle and buzzing under load are two different things...
I test transformers at 144V 60 Hz (20% high) as a quick check of 50 Hz capability - if current rises rapidly with voltage, it isn't good for 50 Hz. The Hammond isn't rated for 50 Hz so has fewer primary turns. 10% more turns or 20% more core area is required for 50 Hz to give the same core flux as at 60. 10% more wire either way... there ain't no free lunch.
As a note, both transformers were tested at 60 Hz, and the PT275 was tested using its 120V tap - a best-case scenario. Both of the transformers are wound for 115V service only. I have heard that the 115/230V Hammonds are better quality, but I don't have one around to test this. All the rest of my power suppply iron is OOS. It might be interesting to take one of my old Fisher power transformers and subject it to the same test. I also have some old Halldorson iron that might be worth a try.
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