2019-04-08 Output Transformers Construction

from FB group Regenerative Receiver… Apr 8

庄议翔
The power transformers have the laminations interleaved. The first lamination has an E then I, the next one has I then E. So the transformer core does not have any air gaps, because it does not have any DC flowing through the windings.

The transformers for single ended class A audio amps have DC through the winding and this current magnetizes the transformer core. To prevent core saturation all of the E laminations and all of the I laminations are together in a block, and they are separated by an air gap, actually a piece of paper. This prevents the core from saturating. If the core saturates during audio output, the signal gets clipped and it sounds distorted.

When I was young I needed copper wire so my favorites were output transformers from AA5 5 tube radios, typically 50C5 tubes, and I took the transformers apart and used the wire. The disassembly was easy because the I laminations were one solid piece, the core came apart easily, just a little bit of work to remove the windings. Power transformers from old TVs were a lot of work because each E and I lamination had to be removed and it took a long time with a hammer and chisel to break up the laminations. But I didn’t have money so I used what I had. By taking apart transformers I learned about how they were made, and I broke off the glass of dead tubes and saw how they were made of fine wires and a few pieces of mica insulation. It was amazing how simple a tube (valve) was, yet could do magical things, like pull RF signals out of the air and turn them into music and voices. 😮 😊

I believe what you say about the B-H curve. What I do now is buy a 70V line transformer made by Bogen, it’s a T725 which has multiple taps and is popular with the crystal radio makers.


7 Responses

  1. John Stumm says:

    Ah, the venerable T725. I’ve got a couple that I used in making crystal radios. No longer needing them, I tried to sell on ebay for cheap, but alas, no interest. I also am in possession of dozens of transformers of all types from several KVA to small signal types. Hate the thought of scraping, but no one seems interested in them. many suitable for 12 volt PS’s except everyone’s using switching ones now. Hate the prospect of junking. I’m still obsessed with transformers, now it’s making TLTs using ferrite cores for ham radio use. Sold dozens on ebay. The key difference, they’re light weight!

    • admin says:

      I have a lot of ferrite cores and make many toroids for various purposes. If you’re using toroid cores, they must be large, and expensive, too.

      • John Stumm says:

        I’m using toroid cores to a certain extent but my bread and butter are dual beads laced together binocular style. I have found sources for them, (type 43) that are cheap. This allows me to sell for $5. Search Dual ferrite bead 9:1 unun. Sold 43 of just my small ones. I love All Electronics and Surplus Sales of Nebraska! JPMultiserve for ancillary materials too.

      • John Stumm says:

        I’m curious if you got my reply to your brief response. I don’t see it posted. Was it meant to be private or perhaps it did not go thru?

        • John Stumm says:

          Ok, apparently it didn’t go thru. Anyway, aside from using toroids, my bread and butter ferrite material are beads that I fashion binocular style and with a few turns of wire laces thru them, I get a good performing impedance matching device for dirt cheap. My small ones go for $5 on ebay. Larger, more hi power ones a little more. Search Dual Ferrite Bead 9:1 unun. Easy to make, cheap to ship.

          • admin says:

            One problem I have is my old hosting svc had set up so the comments, etc would notify me by email. The new hosting svc isn’t set up for notifications yet. I’ll have to look into that and see about fixing it. So anyway I’m forgetting to check it daily for comments to approve. I apologize.

        • admin says:

          I had not yet approved it. I think once I approve a person’s comment, then it auto approves subsequent ones. I can’t let comments be auto posted because there are many more spam than legit.

          I’ve bought toroid cores from Surplus Sales, also. I usually order a bunch from Mouser. I just got some 2643001102 (IIRC) binoc cores. But I have been using mostly 5943 whatever’s both from Fair-Rite.

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