I am currently in the process of designing a rough SE output transformer for an "experimental project". Since this is new territory for me, I purchased a large(and cheap) power transformer and I disassembled it for the bobbin and EI laminations. The original power transformer was rated for 500VA but I honestly don't expect more than 70W or so. I have my turns ratio and such already calculated out but I still have a small dilemma; air-gapping the laminations.
I've been reading around and some people reportedly created a very crude air gap by stacking the E laminations on one side of the bobbin and the I lams on the other side and using a piece of paper to create a gap.
This picture isn't mine but it pretty much shows what I'm describing:
http://www.richieburnett.co.uk/choke1.jpg
I have attempted to do a "mock stacking" using the same technique but I can't seem to get the Es and Is to line up as neatly as seen. Also, the mounting brackets I have will not work for this method.
Is there any another way to stack and air-gap the laminations?
I've been reading around and some people reportedly created a very crude air gap by stacking the E laminations on one side of the bobbin and the I lams on the other side and using a piece of paper to create a gap.
This picture isn't mine but it pretty much shows what I'm describing:
http://www.richieburnett.co.uk/choke1.jpg
I have attempted to do a "mock stacking" using the same technique but I can't seem to get the Es and Is to line up as neatly as seen. Also, the mounting brackets I have will not work for this method.
Is there any another way to stack and air-gap the laminations?
This is how SE OPTs are made, some sort of insulative material a couple of /100ths of a milimeter thick. Since laminations aren't interleaved, they need screws through depth of the entire stack (usually in corners) and brackets on each side. These also help to align the laminations.
Just an idea: you might want to make a jig out of wood, in which to put the laminations so they line up neatly before applying lacquer.
Kenneth
Kenneth
Back when I was young and had more ambition, I made two audio output transformers from laminations from two power transformers. I wound high quality electricians tape on the laminations before winding the wires and covered the layers of the wires with electricians tape. The primary and secondary were intreleaved a couple times in both transformers according to an article I read and I included screen taps for use in two ultralinear/distributed load/partial triode type push-pull amps. The sound quality was very good and had a unique warm quality. After comparing them to a number of other amplifiers that use output transformers with paper insulation and/or is potted tends to make me believe that transformer insulation can be a factor in the sound quality. The vinyl tape seemed to be an improvement compared to paper. Teflon plumbers tape might give good results. I never tried teflon, though.
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I wound two wires at the same time so that the wire in each half of the transformer followed the same path. You have to connect the two windings so they're phased right.
"I've been reading around and some people reportedly created a very crude air gap by stacking the E laminations on one side of the bobbin and the I lams on the other side and using a piece of paper to create a gap."
I don't know how you mean "very crude", that's generally how it's done with laminated or tape cores.
I don't know how you mean "very crude", that's generally how it's done with laminated or tape cores.
Thanks for the replies guys!
Kavermei - I do not intend to varnish the transformer; it will be dry stacked and held together by bolts. For my application, I just need something that works; I'm not too concerned about the sound quality or anything.
7n7is - The bobbin I am using is "partitioned". I will wind the primary on one side and the secondary on the other side. I do not plan to do any UL or 4-8-16 ohm taps so the winding should fairly straightforward; it will be a simple 8K:8 transformer.
Kavermei - I do not intend to varnish the transformer; it will be dry stacked and held together by bolts. For my application, I just need something that works; I'm not too concerned about the sound quality or anything.
7n7is - The bobbin I am using is "partitioned". I will wind the primary on one side and the secondary on the other side. I do not plan to do any UL or 4-8-16 ohm taps so the winding should fairly straightforward; it will be a simple 8K:8 transformer.
Once you get it working you should probably at least drop varnish on the cores until no more will soak in, otherwise you might end up listening to the transformers even more than you'd planned.
This transformer will be used for experimentation; I don't even know what kind of currents to expect and there is a very real chance that I could fry the primary. I want to be able to disassemble and reassemble everything quickly without the hassle of removing varnish residue, re-varnishing, etc.
Nooooooo! Knock out those sections, use a flat bobbin. Side-by-side you won't get anything above 5kHz, the leakage inductance is huuuge.
The best simple compromise is P-S-P, so you wind half the primary, then the whole secondary, then the other primary half. It's not great, but it's not bad either, and should get bandwidth out to 30kHz or so. Quite an improvement, and quite useful for the audio range. 🙂
Tim
The best simple compromise is P-S-P, so you wind half the primary, then the whole secondary, then the other primary half. It's not great, but it's not bad either, and should get bandwidth out to 30kHz or so. Quite an improvement, and quite useful for the audio range. 🙂
Tim
@db!
even if you are using sectioned bobbins, you can still do interleaving....scrambled winding is easier to do on a sectioned winding.
even if you are using sectioned bobbins, you can still do interleaving....scrambled winding is easier to do on a sectioned winding.
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Sch3mat1c - I am anticipating a fried primary sooner or later, I want the primary and secondary on separate sides to facilitate easy rewinding. The laminations are probably isn't grain oriented steel so I'm not expecting good frequency response.
Tony - Are you referring to the windings or the laminations?
Tony - Are you referring to the windings or the laminations?
I have to agree with analog_sa here, I once accidentally shorted a (power) transformer until the varnish started fuming and the core started 'ticking' because of thermal stress, but the windings held up and there was no permanent damage 🙂 So I think there are enough early warnings, such as core temp., before a winding would actually burn out!
The thing is, I'm going to be running this transformer with various large transmitter tubes. Most of the tubes I'm planning to use have never been used before and I'm not sure what kind of current to expect.
Since you guys seem pretty confident that I probably won't blow the primary, I will cut out the partition and try interleaving the primary and secondaries...
Since you guys seem pretty confident that I probably won't blow the primary, I will cut out the partition and try interleaving the primary and secondaries...
The enamel wire I am using is rated for 3500V; I don't think I'll be going that high just yet. As for the tubes, I am experimenting with a large variety of tubes. Some of the tubes I plan on using are GK-71, 211/854, 833A, Eimac 4-xxxA series and various other russian transmitter tubes. I am planning to "create" various primary impedances by using different impedance speakers on the secondary.
The B+ will be pretty high, I plan to have it in the 1.5 - 2.5kV range. Now, before someone starts harping on how dangerous this is and why I should abandon this project; I'll have you know that I've been in the HV scene for a long time. I've managed to build and operate tesla coils, jacob's ladders, marx generators, etc without getting zapped/killed. I'm pretty confident that I can handle 1.5 - 2.5 Kv
The B+ will be pretty high, I plan to have it in the 1.5 - 2.5kV range. Now, before someone starts harping on how dangerous this is and why I should abandon this project; I'll have you know that I've been in the HV scene for a long time. I've managed to build and operate tesla coils, jacob's ladders, marx generators, etc without getting zapped/killed. I'm pretty confident that I can handle 1.5 - 2.5 Kv
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