Building a transformer

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

You haven'''t got a basic f****ng clue have you. Here we are going for rentry and some idiot wants to wake up Jim for the recip for fried eggs. The air sytem might be loaded but we're 15 minutes to slash and two minits from scoff with ALL the trimmings and someone wants to check the database.

Absolutlyee blodddy amaxzing.

DNA

Taking out the old secondary is almost trivial, with a hacksaw and a chisel. ;-)

But apparenlty, you need to add windings to the primary to bring the magnetizing current down, or somethiing like that. I have an old MOT that I've been experimenting with, and the idling current is just way too much for any self-respecting 60 Hz trannie, albeit they do have to account for the shunts, which current-limit the output.

On and off, I've been poking around with this thing, but now I'm at a crossroads with it - do I cut it open, take the bobbin out, and enhance the primary that way, or do I thread more #18 Formvar wire through it until I build up another layer of windings? So far, threading the new wire through has turned out to be much more of a PITA than I had expected, so it's kind of on the back burner for the moment.

Good Luck! Rich

This might be a good candidate for a triac phase fired circuit such as:

These can be noisy, but they are very efficient, and low in cost.

If you want to make your own transformer,

Most importantly, consider exactly what you need the supply for, and build, buy, or modify according to the exact specifications you actually require. You must look at efficiency, weight, size, line and load regulation, max and min voltage adjustment, ripple, noise, overshoot or droop on load change, response time, cost, and time to design, build, and troubleshoot.

You can get so much high quality equipment on eBay and at electronic flea markets, that building your own is usually only for very special requirements or as a learning experience.

For logic circuits, I would recommend a separate 5 VDC (or 3.3, etc.) designed for that purpose, with a good crowbar overvoltage protection circuit. A wide range adjustable bench supply can too easily generate a spike that will wipe out (or incrementally damage) all the logic circuits. It might be a good idea to put a crowbar on the logic board.

Good luck,

Paul

Yea I know. That's very common in the audio industry but we Engineers should know better and use the proper terms. America is stupid enough without us adding to it, don't ya think?

I've run out of library shelf space, so I've been donating out of date books (like "Mother of All Windows" for Win95) to charity book sales ;-)

...Jim Thompson

It's in my GE handbook from 1973. ISTR some magazine article from 1971 using it, but I'm not going up in the attic dusting off that pile of old mags.

- YD.

Look for a surplus transformer, you won't save any money trying to build one yourself.

That's a BIG supply to be using a linear regulator for, I suggest looking at some of the switcher IC's available now days, National Semiconductor makes a series called Simple Switchers which are FAR easier to work with than designing a switcher from scratch and they have HV versions which are good to 80V or so.

Wasn't that around the time the Dynaco ST-400 came out? I rebuilt one of those once, seems like it used a bunch of big Motorola power transistors, I forget the numbers but they weren't 3055's. Seems like there were 4 of each polarity per channel, or maybe it was 2, I do remember the heatsinks were HUGE.

In message , dated Wed, 9 Aug 2006, James Sweet writes

Many manufacturers used 'custom' devices which were allegedly tested to custom specifications by the device manufacturer. The Vcc max might be higher than for the normal device, and/or beta range might be less.

In message , dated Wed, 9 Aug 2006, ArameFarpado writes

Does nobody know how to calculate rectifier circuits any more?

This will need to be a 900 W transformer.

"James Sweet"

....... Phil

In message , dated Wed, 9 Aug 2006, Phil Allison writes

My 303 suffered its second elco failure recently, and an elco in the 33 preamp came out in sympathy. Coincidence. Of course, I put new elcos in both channels.

I've replaced 40411s with 2N3773.

Graham

I have to agree with the sentiment 100%. Surplus transformers are always going to be cheaper than custom-built :-). Most oddball transformers on E-bay sell for pennies on the dollar (actually most don't sell at all!)

And construction and mounting-wise, a lot of small transformers are way easier to deal with than one mammoth one. Above a very small number of VA you start building the case and mounting reinforcements around the transformer anyway :-).

Tim.

Very small transformers have large numbers of turns and the wire is thinner. Somewhere around 50 to 100 VA is a good size to learn on.

If you can get a split bobbin, you will avoid a lot of safety issues.

For winding heavy wire, I find it best (in the absence of a large enough winding machine) to tie one end of the wire to the front gatepost, then lay it down the side of the house and down the back garden path. I walk up the garden, reeling-in the wire onto the bobbin and counting the turns as I go. The tension is easy to control by just keeping a steady pull against the wire.

Carry tools, string, insulation material and adhesive tape in your pockets; you won't be able to put the core down to go and fetch them because the windings will spring undone.

Look for a blown-out 200-400 watt audio amplifier (or receiver) at a garage sale. The transformer you'll find in it will be pretty close to what you want. The amp will also include a lot of other very useful items such as big heat sinks, and so on.

Isaac

u know ...if u really wish to "learn" ...why dont you design yourself a

(i know what some ppl are going to say ....he wants to learn ...not repent)