Old radio transformers

[Bushbaby]

Hi All,
My good friend and colleague Mr Beckett has very kindly collected an Ekco A23 that I purchased from ebay for me today (thank you again kind sir).

He has also sent me some good pics of the set, the case looks excellent but the chassis has a level of rust which, given its age, is probably to be expected as it has been unused and likely to have been stored in a loft for many years.

Having looked at one of the pictures, it made me think about the transformers - how does age and rust affect these. Can they be truly reliable if potentially stored in 'poor' conditions i.e. subjected to damp, humidity and temperature fluctuations?

Thanks in advance for advice.

Regards

Rob

[Mark R]

You may get the dreaded green spot, but other than that I do not know.

cheers Mark

[Yorkie]

Ed Dinning's your man Rob - hopefully he'll spot your post and respond.

If there's any signs of recent damp, I'd be inclined to stick it in the airing cupboard (with Angie's permission of course!) for a week or so to make sure it's well dried out. I don't think it matters if the laminations are rusty - all the iron in the core is there. As to green spot corrosion, I guess it's always a possibility, but that tends to be more of an issue with high resistance headphones, field coils of mains energised speakers, vintage inter-valve transformers, etc, all of which use very fine wire - about 48SWG. Even mains transformer primary windings tend to be thicker gauge than that.

Have fun!

[Skywave]

Comments based on my experience.

Rust on the non-laminations is not that serious, provided that is hasn't gone so far as to render the whole item a bit crumbly. Rust on the surface of the lams. is not too much of a worry, but if the rust has penetrated between the lams. that could decrease the transformer's efficiency. However, considering that the lams. are usually bolted down well-tight, the chances of rust between them is reasonably remote.

Dampness and moisture that has penetrated the windings is a much more serious issue. At worst, you could have total breakdown of the insulation between one (or more) windings to earth / lams. / metal frame. If you're unsure about damp in a power transformer, remove it from its host (noting the connections first ) and store it somewhere warm for a few weeks: an airing cupboard that has a hot water tank installed therein is an old favourite. Then give it an insulation test with something like a 'Megger' prior to its re-installation and power-up.

I have met one example of an ancient mains transformer where a low-voltage winding used D.C.C. wire for its insulation. If damp gets into that, there could easily be a problem rendering the whole transformer U/S: the D.C.C. wire 'insulation' fails; you get a shorted turn.

I have never known of the 'green spot' problem in mains / output transformers, but that doesn't mean that they aren't affected that way.

Al.

[Mark R]

Al
good points. I personally have not had green spot in mains or output TX. Usually in the coils, I dare-say they may affect the mains tx though.

cheers Mark

[tiv48]

as mark said green spot can be a problem more so on if transformers ,a mains transformer can be checked with a megger .
one i had was compleatly rusty and showed signes of green at connection points .i wire brushed the lamminations then varnished them ,resoldered all connections then baked in the oven for 20 mins at 100 deg for 20 mins it is still working now 15 years latter
rob t

[AlanBeckett]

Just to put it into contex, see attached.
Alan

   

[Joe]

Doesn't look like any cause for concern there.

- Joe

[tiv48]

yep seen worse
rob t

[Andrewausfa]

Mine was broadly the same, no problems with it. Nice use of a 5Y3.

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