How to make mic input transformer 150:50KCT for mic tube preamp???

[delipasha]

I would like to make a mic tube preamp, and originally the UTC-A11 is used, which has several impedance possibilites in the primary which in my case isn't neccecery. I know that I could buy the transformer I need, but I would rather like to make it myself. I've been reading a lot about transformers, but no one talks about making one, just buying it.

Does someone know exactly what thickness of wire is required for primary and secondary windings, how many windings in primary and secondary, the core size and other details for a input mic transformer which would be 150 ohms to 50k ohms. (the secondary in UTC A11 is a central taped tran.)

[DF96]

I suspect there is a very good reason why few people make their own transformers, especially mike transformers.

[Michael Koster]

Originally Posted by delipasha

I would like to make a mic tube preamp, and originally the UTC-A11 is used, which has several impedance possibilites in the primary which in my case isn't neccecery. I know that I could buy the transformer I need, but I would rather like to make it myself. I've been reading a lot about transformers, but no one talks about making one, just buying it.

Does someone know exactly what thickness of wire is required for primary and secondary windings, how many windings in primary and secondary, the core size and other details for a input mic transformer which would be 150 ohms to 50k ohms. (the secondary in UTC A11 is a central taped tran.)

So you really don't want to learn about transformers, you just want to turn the wire? Maybe try the Prodigy Pro DIY forum. There is a fellow called CJ there who takes apart vintage transformers who may have the details on the A-11. Dang, I just sold a pair of A-11s on ebay...

[delipasha]

Thanks! I will check it there.

Of course I would like to learn, and I am, but I wasn't able to find any useful material on input and output transformers. I found good tutorials for making power transformers, both theoretical and practical ones, and recently I've started learning electronics, but it takes a lot of knowledge to "invent" transformer from scratch, that's why I asked so directly.

[dchisholm]

Originally Posted by Michael Koster

So you really don't want to learn about transformers, you just want to turn the wire? . . .

For many centuries - probably millenia - apprentices learned an art or craft by studying and mimicing the work of an artist or master craftsman. If "delipasha" has an interest in mic input transformers, I have no objection to this approach. He just MIGHT, with a little guidance, learn a LOT about the subject and create some very admirable designs. At the very least he may simply accumulate an understanding of the obstacles and complexities hidden in the devices. Somewhere in between he may receive the satisfaction of creating a useful object from his own efforts, no matter how excellent or mediocre the performance.

At the age of 11 - nearly half a century ago - I crafted an audio amplifier from instructions in a book. In retrospect it's almost comic in its simplicity: three transistors as I recall, powered from a stack of D-cells, providing a fraction of a watt to a speaker. The instructions were quite detailed, including sketches of parts layout and point-to-point wiring, tests to identify construction errors at intermediate points in the assembly, etc. I understood very little of the circuit's explanation, which covered several pages, and agonized over whether an extra half inch of chassis depth would affect performance, and what would be a suitable substitute for the 2N217. In fact, most ANY small-signal PNP would work in that circuit - but I was still several years from understanding how that could be. I suspect that many (perhaps most?) of us here on this Forum can point to similar experiences - indeed, we probably wouldn't be here if it were not for such experiences. At some point, "delipasha" may say similar things about his seminal efforts with mic transformers.

We can suggest that initial study and analysis my be a more efficient way to learn - that is the nature of the present age. It also subtly belittles the complex and unique attributes of individual persons. In various design engineering organizations over the years I have witnessed, or been a party, to the explosive growth of individual knowledge during ad-hoc activity after somebody uttered a phrase similar to "HEY! I never noticed THAT before!". (Often, this phrase was uttered in conjunction with an "Unscheduled Development Test" (UDT), such as connecting a supply voltage with reverse polarity.) The analysis, study, refinement and documentation followed AFTER the activity. The 20th century essayist and physicist Dr. Jacob Bronowksi stated a preference for activity versus study when he said:

"The world can only be grasped by action, not by contemplation. The hand is more important than the eye ... the hand is the cutting edge of the mind."

I have no special passion for mic transformers, though many incarnations ago I could appreciate the difference between Deane Jensen's products, and some hunks of copper and iron salvaged from the junk box at WHDF. As already mentioned I can't think of a single DIY or construction article for a mic transformer. Carefully dissecting somebody else's work is probably as practical an approach as any.

If I wanted to pursue the topic, a basic circuits text (is Hayt & Kemmerly still in print?) would give you the rudiments of turns ratio and winding inductances. I suspect the "Radiotron Designer's Handbook" would be MUCH more useful, at least with the experience I've accumulated. That may be all one needs to create your Prototype Mic Transformer S/N 001.

Then begins a cycle of measurement, evaluation, and experimentation. There ARE people crafting their own output transformers, and if you categorize both "mic transformers" and "output transformers" as "audio transformers" then there are probably some similarities in the problems of bandwidth and parasitic elements. At a later stage there may be something that can be learned from radio amateurs who home-brew wideband. low loss, RF transformers. Or perhaps not - 3 or 4 decades of frequency span is a LONG ways to extrapolate the techniques that work in one application to another application.

So give it a try, "delipasha" - and let us know what you learn.

Dale

[delipasha]

Thank you very much, Dale! I share that approach 100%. I would like exactly that, to understand the principle of an input transformer through couple of real, practical examples. My intention is not to make a better transformer than I can buy, it is to make one that will work in a first place.

Thank you very much for your effort and good intentions!

Marko

[Doz]

Dale, That was stunning. I am almost brought to tears.

[DF96]

Originally Posted by dchisholm

The 20th century essayist and physicist Dr. Jacob Bronowksi stated a preference for activity versus study when he said:

"The world can only be grasped by action, not by contemplation. The hand is more important than the eye ... the hand is the cutting edge of the mind."

I suspect that Albert Einstein and Paul Dirac, to name but two, might beg to differ. They both made major advances (general relativity and antimatter, respectively) in our understanding of the universe simply by thinking.

[dchisholm]

Another Resource

You might get a little information if you ask in the Yahoo "micbuilders" group at < micbuilders : micbuilders >. These folks seem to be mostly into home-brew microphones based on commercial electret capsules, but a few of them have displayed some impressive machining and fabrication work so perhaps somebody has undertaken a home-built transformer at some time. The "Files" and "Links" sections include a few articles where authorities have commented on the desired characteristics of mic transformers, and a photographic copy of "Radiotron Designer's Handbook".

Dale

[delipasha]

Thank you very much, Dale, I joined the group on yahoo, and yesterday I found the book and started reading. It is great!