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Old 13th Jun 2020, 5:44 pm   #1
AndyWright
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Default Gardners GR29574 transformer

Hello

I've acquired a Gardners GR29574 transformer as part of a partially built power supply. The pin are labelled 1 through to 29. Does anyone know what the exact pinout and capabilities of the transformer are, google has drawn a blank.

Thanks

Andy
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Old 13th Jun 2020, 7:39 pm   #2
Ed_Dinning
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Default Re: Gardners GR29574 transformer

Hi Andy, if you can post a pic it might help.

Ed
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Old 14th Jun 2020, 7:51 am   #3
trevatxtal
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Default Re: Gardners GR29574 transformer

As a young apprentice I was studying Mechanical / Electrical Engineering at Gardners Factory in Christchurch Hampshire. now Dorset.
The Factory made thousands of different Transformers one offs to tens of thousands off, but I never recall a transformer over 500 watts,to set up the many hundreds of coil winders in the winding shop, was part of my training, but the female operators or winders as we called them were 100 times faster than I ever could be.
Now to the transformer a Photo please !
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Old 14th Jun 2020, 9:39 am   #4
AndyWright
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Default Re: Gardners GR29574 transformer

Hello

here's a photo of the transformer. Its roughly 5.5" X 5.5" X 6". The wires at the bottom of the photo are allegedly the mains, Terminals 9-13 have been labelled as the HT on the chassis. 550-490-0-490-550, though I've not tested them.

The terminals at the top are labelled as heater windings on the chassis. I'd really like an idea of the current capability of the transformer.

Andy
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Old 14th Jun 2020, 10:58 am   #5
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Default Re: Gardners GR29574 transformer

The anti-creepage slots punched around terminals 9-10 suggest a particularly high voltage- I wonder if this is from an oscilloscope, or some other device with a CRT like a radar or sonar display? It would certainly hint to me that I needed to be wary when powering/measuring its capabilities, I wouldn't apply a cheapie analogue or digital meter to those particular terminals!
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Old 14th Jun 2020, 12:34 pm   #6
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Default Re: Gardners GR29574 transformer

I'll bring it up gently with the variac and see what voltages appear on those terminals.
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Old 14th Jun 2020, 1:45 pm   #7
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Default Re: Gardners GR29574 transformer

I've done some tests with the voltmeter and variac, and the ht windings are as advertised. All the heater windings are 6.3V. If anyone comes across any info with regard to the current capabilities that would be most useful.

Thanks
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Old 14th Jun 2020, 6:44 pm   #8
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Default Re: Gardners GR29574 transformer

You can work out the current capability from the winding resistances. I do not know the power capability of a transformer of this size.
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Old 14th Jun 2020, 7:54 pm   #9
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Default Re: Gardners GR29574 transformer

A rule of thumb, although it is crude, is to load the winding until the voltage drops 10% below its off-load value. The current which is flowing then will be indicative of the maximum which can safely be drawn. If you only load the windings one at a time the answer you get will be on the high side though since it will reflect the copper losses in the secondary only. Copper losses in the primary and iron losses in the transformer as a whole will be much reduced unless all the secondaries are loaded.

Cheers,

GJ
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Old 14th Jun 2020, 11:21 pm   #10
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Default Re: Gardners GR29574 transformer

I found this on a Chinese website. I cannot vouch for its accuracy. Not sure what "English big bull" means. I just hope it's not bull....
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Old 15th Jun 2020, 6:03 am   #11
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Default Re: Gardners GR29574 transformer

Quote:
Originally Posted by barretter View Post
I found this on a Chinese website. I cannot vouch for its accuracy. Not sure what "English big bull" means. I just hope it's not bull....
Brilliant find sounds just right from it size Most of Gardner's Transformers were over engineered by 50% at least, although this model is in the cheaper class (Hot varnish dip I think) they were still made to a high standard and if I recall right all winding's were flash tested at 5Kv between all winding's and also the core.
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Old 15th Jun 2020, 6:09 am   #12
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Default Re: Gardners GR29574 transformer

Big bull head must be a literal translation of idiomatic Chinese. The Double C bit is obvious, the transformer is constructed with C-cores. So the bull head bit could just refer to it being a transformer which is missing from that descriptive string.

Notice there.s no 5v rectifier heater winding.

The data content, with current values makes it look like whoever got hold of one of these transformers in China, also got hold of some of its paperwork.

Let's do a reality check

6.3v at 6A twice is 75.6W
6.3v at 6A again is 37.8W
6.3V at 2A three times is 37.8W
530V at 0.3A is 159W

That totals 310.2W and doesn't seem far out for an 8kg transformer.

If someone assessed current capabilities based on 10% drop, they wouldn't have come out with such round numbers and the heaters wouldn't have been so closely related. Those figures look like they're from a manufacturer's spec sheet.

Well found, Barretter!

David
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Old 15th Jun 2020, 9:27 am   #13
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Default Re: Gardners GR29574 transformer

Compared to the specimen in baretter's link, I'm still intrigued by what are probably milled, rather than punched, slots in the example in question- I wonder if there was a leakage/tracking problem with that composite top plate and if this was addressed after the event, or if this was something that was done as a production amendment. 500V-ish shouldn't be particularly stressful but once tracking has kicked off, it can be persistent and insidious.

It certainly sounds like a very capable transformer and would attract a fair bit of interest from the amp builders, whether with choke-input filtering for more mainstream HT applications, or capacitor-input for more brawny EL34/KT88-style designs looking for 600V or so. I'm thinking that the generous spread of 6.3V windings suggests use with later rectifiers like the EY84.
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Old 15th Jun 2020, 9:53 am   #14
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Default Re: Gardners GR29574 transformer

Might be a later version of the teminal plate shared with a much higher voltage HT winding in a derivative of that transformer.

There could be many reasons, and not all the reasons may apply directly to that transformer.

If the slots were for voltage/creepage and some 6.3v windings were for rectifiers, then wouldn't the rectifier heaters have had similar slots between them and other things nearer ground?

Nice transformer, though.

David
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Old 15th Jun 2020, 10:04 am   #15
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Default Re: Gardners GR29574 transformer

True- it's just one of those things that stuck out on first looking at the pic. The tag layout on those transformers and the steel-can types often seems to have a curious rationale behind it!
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Old 15th Jun 2020, 5:28 pm   #16
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Default Re: Gardners GR29574 transformer

The slot is milled and the transformer if I recall was for a Oscilloscope, that had a voltage treble'er in it for the anode voltage of the CRT tube so voltages could be accumulative, of course that model got into many other items.
The panel was Paxolin (paper and resin) good insulator until overheated then would corbonise.
Gardners must have produced thousands of them.
The C core was in two halves and kept together with a steel band like packing case band.
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