Rewinding a 100va transformer

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You will never be able to wind the transformer as tight as the original and the windings will hum unless you bake it.
 
It's probably about 5 to 7 turns per volt and the 6.3v winding will give you some idea. But where are you going to buy the insulating mylar. The mess is probably due to the mylar melting.
It probably has 2 or 4 x 285v windings to get 570v HT. Check the value (V) of the electrolytics and see if one is above ground.
 
Now thats more like it, thanks Col.

I served my time rewinding motors, I cadge bits of stuff from where I used to work now and again, I'll be able to get some copper wire and insulation from there, this trans has a clear layer, I dont think thats something I'll be able to get, however I'll get something designed to take the voltage and temp, most stuff these days is class h, so it'll probably be better than the old anyway.
 
Hi,

Long, long, long, long time ago, i had a scope with a similar problem. The transformer was bad. The secondary was something like 1000vac and i didnt have anything like that. I took out the transformer, tried to get the windings off, peeled apart lamination, ended up with a pile of garbage.

That was the only scope i had, so i had to think of something. I ended up putting two or three lower voltage transformer secondaries in series to get the higher voltage. For example (dont remember the exact voltages now) one 200vac, one 400vac, then maybe one 300vac gets me close to 1000vac. The secondaries MUST be isolated from the primaries or this wont work.

The lower voltage transformers were common in amplifiers and radios and TV sets back then. They were still quite high by today's standards (being 200vac or higher in most cases) but not enough for the scope. A few strung together did the trick and the scope worked for years after that.

As a side note, it did not cost me one penny to do this because i had all of the lower voltage ones already removed from older equipment.
 
Also a long time ago I worked in a repair centre that had a 'scope a telequipment I think, it had a row of transformers bolted to the back of it, I think it had a similar thing doen to it.
These days such trannys are a rareity, and I'd rather do the job with one.
There is a 100va transformer kit on ebay right now, that might save me some ache.
 
dr pepper, I have some .09mm thick, "Nomex" Insulation I could mail to you in a letter. At NO Charge to you.
I wind a Lot of Transformers and Its perfect for insulation between the HV Layers.
And I have Thicker pieces of Nomex also.
This was all from a Transformer & Motor Repair company that went out of business.

I also have Most sizes of Enamel Wire between 18 AWG to 40AWG in mostly 8 Pound rolls.
Could send smaller quantities, But the shipping cost to the UK on it is TOO Much to be practical.
 
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Hi,

Also remember when winding transformers to use tape between layers to add extra insulation between top and bottom layers which have higher voltage differentials than turns that are side by side. Going across once with one layer and then winding another layer on top going the other way means the other end has the voltage of two layers across two turns rather than just the voltage of one turn. A good tape to use is mylar, if you can find it.
 
Ok then.

Thanks chemelec, I might take you up on that, however I managed to scrounge some stuff today, this stuff is trivoltherm nkn made by krempel, actually the firm that produces it is jones stroud insulations and they are only a few miles from here, its glass fabric - polyimide film - glass fabric, its sposed to be the best they do.
I have collected a few offcut pieces from behind the guilloteen, plenty for a dozen trannys.
If it doesnt work then I'll go for nomex.

Still not braved cutting up the transformer yet, the probelm is I will break off the leadouts loosing which winding is which.
Anyways once I have an idea I think I'll start from scratch and calculate a new design using the original core lams and make a new bobbin former.
 
OK I found the service manual, seems I'm going to have to use some caution winding this.
I think I'll cut off all the old junk and bin it, and design again from scratch, except maybe for the wire sizes I'll be able to measure those still.
The o/p's are:

0 - 150v

22 - 0 - 22v

0 - 1kv - 1.2kv (1kv only used)

0 - 40v

0 - 6,3v

0 - 120, 0 - 120v primary

The 1kv is the one thats going to take some care with to avoid flashover.
 
dr pepper said:
OK I found the service manual, seems I'm going to have to use some caution winding this.
...

The 1kv is the one thats going to take some care with to avoid flashover.
Click to expand...

It might be worth considering a separate 1kV supply, generated from one of the other outputs, the current is going to be pretty small, and isolating the 1kV on a separate board might be a reasonable way forward. Does the 1kV go directly to the CRT, or are there voltage doublers or whatever elsewhere in the scope?

Perhaps something along these lines..
http://tubetime.us/?p=183
 
I would assume that 1KV is probably a 40 AWG Wire.
And Probably the most Outer Layer?
If you Carefully Layer Wind it with Nomex between layers, it should be OK.

I'm just not sure What Equipment you have for winding such transformers?

I do High Speed Winding on my Metal Laithe, using a Digital Counter for a accurate count on the number of turns.
 
Yes it looks about 40 swg, and I think it is the outer layer, not surprising as it'll be the lowest current.
I have a myford lathe.
I now have the manual for the 'scope, I could put together a smps for 1kv if that was absolutely necessary.

1kv from the trans goes through a load of electrolytics then to the tube via a couple of rectifier diodes, no multiplication.
 
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A Laithe is Good, but do you have a Turns counter you can add to it?

It is fairly Unusual for transformers to burn out, UNLESS there is other problems.
Possibly a Bad Filter Cap on one of the supply lines.
 
Yup both a counter and a calculator modded to count.

Yes the seriesed up caps on the 1kv line are suspect.
 
Just a thought her on the alternative of using two transformers.

For the 1 KV circuit it's likely that that circuits actual working current is very low ans could be easily enough created using a common 115/230:230/460 isolation transformer followed by a simple rectifier and capacitor voltage multiplier circuit or for that matter a 1:1 or 1:2 transformer and a multistage voltage multiplier thus eliminating the need to wind a HV winding all together.
 
chemelec said:
A Laithe is Good, but do you have a Turns counter you can add to it?

It is fairly Unusual for transformers to burn out, UNLESS there is other problems.
Possibly a Bad Filter Cap on one of the supply lines.
Click to expand...

Hi,

Yes that's interesting. I think i've only seen one or two regular wall warts burn out due to an open winding. I've had a regulated one blow out but im not sure why.
 
High voltage windings cab fail due to insulation breaking down, and they usually have fine wire windings so wouldnt take much burning out.

Yes I have generated 1kv before, quick and dirty, it was a 240v to 12-0-12 transformer, ran push pull from 12v with a doubler on the end, it gave over a kv, it does put double the strain on the windings and you have to run at a higher freq to avoid saturation, if I can get a reliable secondary wound on the original trans I will do that.
 
Doc,
just to humour me, have you determined what is the CRT type?
I thought you said the CRO has transistor amplifiers. Is that correct?
If so, the design is not that old; given of course that my Tek 564 was new in 1960!!.
AND, can you post the manual.
please.
 
Not yet I think the tube's label is under the mu metal, or it hasnt got a label.

The amps and osc's are tranny's yes.

I think its around the 80's era looking at some of the date codes.

I cannot post the manual, the site says the pages are too big to upload, the manual is on pdf's one page at a time.
 
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