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Old 22nd July 2014, 02:41 PM   #1
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Default New or Old Output Transformer?

I need a replacement output transformer for my 1937 Hammond BC organ.

I've found one brand new one that's fairly similar, but not exact. The mounting type is also different. It isn't critical for it to be 100% the same as the old one, but I would prefer it to be!

I don't know the specs, so can't get a copy made. I can't afford a rewind right now either, the repar bill for this organ must already be about 500 (ouch)! I've been offered an output transformer from another Hammond BC. This one is also about 75-80 years old. I was told it was working perfectly before it was removed from the organ.

I've been told by one person (who is biased when it comes to swapping valve for solid state amps) that these output transformers usually don't work now. Through normal usage, do you think these transformers will still have another few years left in them, even at 75-80 years old?

I was thinking, if I can get this replacement to last a couple of years, I'll have no problem affording a rewind of mine by then. Should I take the plunge and get another 75-80 year old output transformer and hope it works another 2 years or so, or should I just buy a brand new replacement as close as I can find?
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Old 22nd July 2014, 02:46 PM   #2
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I would contact Majestic Transformers; Majestic Transformer Co, Poole, Dorset BH12 2HQ | iDorset they will take the old one apart and remanufacture it, in fact they may even have one.
An excellent service and I have used them for years.
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Old 22nd July 2014, 02:58 PM   #3
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I've contacted them, am waiting on a reply from them.

I don't have much money now with this repair bill, so I was just wondering if getting another 75-80 year old transformer will get me by for another 6 months - 1 year as a cheap option for the time being until I can rewind my transformer.
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Old 22nd July 2014, 05:31 PM   #4
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Output transformers don't really wear out, They are nothing more than a spool of wire wrapped around a bobin. They can get burned out when an output tube goes bad or it becomes shorted in some way or another. You do need to know the values of the primary and secondary winding, changing those values will result in very different sound. If you know those values of both your older one and the current one you will know if it will work or not. They are many manufacures of new transformers like Edcor, Hammond Mfg and others.

Last edited by mark02131; 22nd July 2014 at 05:32 PM. Reason: spelling
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Old 22nd July 2014, 06:05 PM   #5
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I know the primary and secondary impedance values - 1300 Ohms primary, 15 Ohms secondary. In the US, the transformers were actually made by Hammond themselves, but as it was a much smaller operation in the UK, they were contracted out to Haddon Transformers who are now no more. But as everything with Hammond, it's very specific and definitely isn't something you'd just find off the shelf. To make a copy, people want more information than that such as input and output voltage and frequency, which I don't know.

I didn't think that it's a sort of part that would wear out with age. Mine only broke because I stupidly managed to apply 435V to it! 435V shouldn't even have been anywhere in the organ, but that much is thanks to a previous owner's modifications and lack of understanding basic Ohm's Law.

I think I'll go with the output transformer I've been offered. Then in a few months, I can get my old one rewound and just keep it boxed up in the organ bench as a spare in case the replacement fails. If it does, then I can get that rewound too, so I'll always have a spare then too!
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Old 22nd July 2014, 09:34 PM   #6
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How do you know the impedance levels? I'm guessing it would have been single ended ? What was the operating idle current through the primary, and the speaker power rating ?

Old transformers typically have a much lower insulation resistance to core (ground) due to the materials available then.

Did the primary winding go open-circuit on your failed unit? Is that the only indication of a fault?

Ciao, Tim
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