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Interstage Transformer Question

S

swbeebe

New Member
Hello,
So I have a stereo DIY tube amp here that was made from a Cary 300B chassis. They basically just kept the power transformer, output transformers, and the power supply caps. They are using an ECC801s preamp tube feeding another ECC801s running the triodes in parallel feeding an interstage transformer that feeds a pair of FL152 tubes for the output. The problem I am having is that one of the transformers has an open winding. I contacted the owner who said his friend built this for him years ago and doesn't recall the transformer value. He said he "thinks" it's 30H on all the coils. (30H primary and 2X 30H secondaries.) I can't say I have ever seen the FL152 used for an audio output tube. Would any of you have a recommendation for a replacement interstage transformer? The guy wants them both changed to maintain symmetry. I was looking at the Hammonds, but I couldn't find anything that looked similar. I am reading about 2kΩ DC resistance on each winding, but my Z-meter only goes up to 1H. I have attached a partial schematic I drew up based on what I found in the unit if that helps any. Thanks in advance.
 

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How big are they? I have some used ones from Wollensak tape recorders, haven't measured them but they may be better than the Hammonds.
 
Physically? They are 2.75" Wide (Metal, not including the ears) X 2.5" (Windings) X 2.25" High. The guy is all about the fidelity. So having something 20Hz-20kHz would be ideal. If I could come up with a decent set of specs, I would have edcore wind me up a pair even. He wouldn't be opposed to that.
 
I have used Lundahl and Onetics IT's with good success. You can't really skimp on an IT and expect great results.
 
Yes, Jack got them made for me. He seems really knowledgeable, and it got the unit up and running. Thanks for steering me to him. It had a bad oscillation when I hooked the first one up at the end of the day on a Friday, and after sweating all weekend about it, it finally came to me about 3am on Sunday, that I must have the primary wires reversed in my drawing causing positive feedback. Swapped the wires on Monday and it solved the problem. I haven't heard good, bad or other from the owner of the unit, so I'm guessing no news is good news.
 
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