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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 30th Jun 2015, 2:56 am   #1
joebog1
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Default English transformer specifications

I have done a search on this site, and googled many many times trying to find data on English made transformer specifications.
By specifications I mean: for power transformers:
Input voltages and taps.
Output voltages and current ratings.
Physical sizes - by that I mean either weight, or dimensions.
For output transformers:
Rated power.
primary and secondary impedances.
Primary inductance.
Leakage inductance.
Half primary to secondary inductance.
Dimensions, or weight.

By weight ( in both cases) I can determine the approximate stack needed to "copy" a design.
BY dimensions I can determine the exact stack that was used origionally.
Even though transformer iron has gone through many changes, and is usually only available made in Asia, ( India specifically make VERY good 5% Si GO laminations, alas only in 14 thou, or .35 mm thickness).
In Australia and USA, transformer specs were very easily obtained, either by a self addressed, and stamped envelope, or by looking in almost any "electronics" magazine. In fact most DIY projects used commonly available, and locally made transformers.
British magazines used locally made transformers too, but specified them as some top secret code.
From valve data sheets I can easily design a transformer that I perhaps need or somebody has ordered from me. There are a few, ( quite a few, in fact) projects in English magazines that making a copy of the transformer is either very hard,
or requires LOTS of experiments to get it right.
In other threads here I have admitted my "love" of 807,s in audio service,
The Brimar 25P1 amplifier and pre-amplifier has interested me for some time, but the only data given is
Partridge type P5352 OR
Savage type 5B29

Does anybody have the specs for these transformers?
A catalogue of Partridge transformers?
A catalogue of Savage transformers?

With thanks in advance
Joe
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Old 30th Jun 2015, 7:48 am   #2
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Default Re: English transformer specifications

The 'top secret code' was the manufacturer's part number, and wasn't so secret, anyone with the cash could order one up.

The manufacturers did publish lists of the ratings and dimensions of their produce. What they didn't publish were the engineering drawings for their manufacture or their design manual.

Where I used to work we had a copy of a large loose-leaf file which listed a large number of bobbins and several sizes of laminations in a few different thicknesses out of which combinations a large number of different stacks could be created. It went on into calculations of turns and wire gauges to design each winding, and then into calculations of temperature for the entire transformer. There were lists of effective rules-of-thumb design choices. With it, you could design a transformer to meet a specification and expect to meet them. A couple of design-make-test loops could see it shrunk by a size or so if you were careful because the design curves were a bit conservative in several respects.

The book had been developed by a bunch of people at corporate 'Galactic HQ' and must have cost a lot to create. It wasn't available outside the firm. You don't want to give your competitors that much help. It converted transformer design from fundamental research into a recipe operation. I can attest to its effectiveness, having done a few designs with it.

Now no-one in various companies designs transformers any longer, this sort of data doesn't need to be a trade secret any longer, but I suspect it's been lost. There are published books on transformer design, but they'll be out of print I guess.

If you pick some lauded hifi design you won't find even the ratings of their output transformers from the original manufacturer in most cases, and they probably weren't in the catalogues of Partridge, Parmeko, Gardners etc. If you wanted to duplicate one, it would come down to getting one and either doing some very careful measurements or else taking it apart to measure dimensions and count turns and not how some windings are positioned with respect to each other.

From a point of availability in small quantities, quite a few magazine articles used ironware from the Radiospares catalogue. RS bought transformers from various sources and it could be fun guessing who made which ones.

There is no rocket science involved, no mythology. The mythology came later. Just imagine the price of a transformer wound in pure silver wire made from bullets previously used to shoot werewolves, with laminations each individually carved by hand by a little old Japanese guy living atop a mountain with only his apprentice watching and learning the craft.

But seriously, they are engineering items and they embody a number of design choices which aren't always readily apparent from an external view or from their ratings. They affect things like saturation limits and distortion.

David
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Old 30th Jun 2015, 8:59 am   #3
joebog1
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Default Re: English transformer specifications

My Dad taught me to wind transformers at about age 10
I specialised in it for many years. I still have half a ton of enamelled wire in various guages, and use a "Glow" winding machine. I also have BIG iron (unfortunately !!! ) from 1 3/4" tongue and up to 2 1/2" tongue. The Glow winding machine was made about 1930 and uses a 1" diameter roman thread, with two brass half nuts. Power is coupled onto it by an industrial "Singer" sewing machine foot operated clutch. Winding tension is arranged by springs and several pulleys, that guide the wire through the winding finger.
English military equipment was very easy to come by in Australia, so I know about the thick varnish that enclosed most English made transformers.
The English military were not interested in audio ( as such) so Ive never had a chance to pull any apart and look at general construction techniques, such as sectioning and insulation thicknesses. I have rewound several Marshall guitar amp transformers, but these are not much better than a power transformer in design.
Thanks for your input anyway
Best regards
Joe
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Old 30th Jun 2015, 10:49 am   #4
kenneth
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Default Re: English transformer specifications

My HOME RADIO catalogue (bought in the 60's and now rather dog-eared) lists some transformers with basic details - see pictures. Can post more if they are of any use. Ken.
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Old 30th Jun 2015, 8:17 pm   #5
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Default Re: English transformer specifications

Surely commercial transformers were designed to be 'efficient' in size, cost and availability of parts. You have no such constraints and can build one twice the size. Something like an AC potentiometer (see the book by Gall) will measure the basic parameters, others come from winding ratios, current rating etc?
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Old 1st Jul 2015, 2:39 am   #6
joebog1
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Default Re: English transformer specifications

Firstly, a special thanks to kenneth!!
and to woodchips, you are absolutely correct.
"Some" English amps were way above standard in performance specs. For their day, AND in a few cases, even still today. This is the reason for trying to find some data on the origionals. I make ( pardon the ego) excellent transformers, but even when they are for my own use, they are, damned expensive, heavy, bulky, and require substantial chassis that also add to cost.
NOT to mention a really good traffo takes me over 100 hours to produce.
I only think I know everything and as my amps are nowhere near as well known as Quad or Brimar or Heathkit ( and I used to make kits)not to mention Marshall or Fender ( NOT that they are such good amps)Vox, etc etc
I try and pickup as much information as I can on what somebody far wiser than I, could produce in a vice holding an egg beater hand drill, in 1950!!

There must have "some magic pixie dust" in there somewhere!!!

Back to kenneth.
What you sent me is perfect!! and I owe you an English ale!! ( yes, I know the difference between lager and ale)
I really dont want to be a pest but can you PM me ? please.
With best regards
Joe
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Old 5th Jul 2015, 10:32 pm   #7
majoconz
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Default Re: English transformer specifications

I haven't read it all the way through, but...

http://www.vintageradio.me.uk/radconnav/homerad.htm
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Old 6th Jul 2015, 1:14 am   #8
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Default Re: English transformer specifications

Thanks again Majoconz!!
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