How do you test transformers?

[old tube]

I’ve got two pairs of old transformers (power and output) to test. One set is Partridge brand (probably around 20-30watt, 5UG4 rectified) from the mid 1950’s … the other Philips (Single ended EL84) from the mid ‘60s. They are European spec i.e. 240V input.

I’ve now got me a decent Variac, so hoping I can, at long last, test these.

Firstly, is it OK to test the transformers with them completely disconnected from any circuitry?

With the power transformers do I simply apply, say, 24 Volts across the input side and read off the voltages on the other side with my DMM measuring whatever B+, heater and rectifier heater (as appropriate) voltages …. AC?

What does one do with the output transformers? I suppose I’m looking to measure the input impedance and also assess what output “taps” they have as neither is marked. I’ve scoured the internet and can’t find anything definitive (well not for my simple mind)

Can post photos, if it’d, help.

Thanks.

[Phil_S]

You have the basic idea. Read here:
http://www.radioremembered.org/outimp.htm
http://www.regiscoyne.com/tech/unknownOT/
http://www.tone-lizard.com/Transformer_ID.htm
...and, of course, here at TAG:
https://tubeamparchive.com/viewtopic.ph ... 062215cafb

I keep on the bench an old filament transformer that has 6.3V and 24.2V secondaries. I usually start with 6.3V input to the secondary on the test subject.

[overtone]

Here's one for the PT from R.G. Keen which i have used.
http://www.premierguitar.com/Magazine/I ... ester.aspx

Congratulations on the Partridge set.

Best, tony

[old tube]

Thanks both, most helpful!

Was going to post it up separately but as they've been mentioned, the Partridge transformers are from what I was told was the PA amplifier from a Fair-ground ride.

Some of the components are pretty interesting, from a bygone age (1950's?)! Love the massive smoothing caps and oil "fillable" caps on the board (assume that's what they are?) .. Bakelite "fuse box" on the outside.

If the transformers and choke work, hoping to build something interesting with them. As I got it, it had an EF40 in V1, ECC40 in V2, 2 x Tung sol 6V6's in the power section and a smashed 5U4G.

[overtone]

bl**dy h*ll, I'd want to test those first too.
You may find that the insulation on the leads disintegrates on touch.

I lived a long time in Brighton, and the name of that amp rang a bell
http://www.pasttimesproject.co.uk/lsl_b ... &story=443

[old tube]

Wow! thanks Overtone. Looked high and low on the iterweb for anything about "Goodsell". Couldn't find anything. Looks like they did some pretty high spec stuff in their day. Obviously the partridge transformers attracted me to this.

The insulation actually is OK, still flexible. Solder is still tight etc. However, will be very careful with this as it's so old. Almost a shame to split it up but I will if the transformers test OK.

[Prairie Dawg]

You can test a power transformer pretty easily but there are a couple things you should do with something this old.

I'd put 1v ac on the primary and see what comes out of the secondaries-that'll give you the ratios as well as the secondary voltages with a little calculating. Make sure and watch yourself on the secondaries until you know what lead is what.

In addition I would probably want to test it with an insulation tester like a megger or an IRT2 to see if there are any high resistance shorts.

[Structo]

Be careful around those old oil caps.

Most of them contain PCB (Polychlorinated Biphenyl)) which is a carcinogen, nasty stuff.

Used in capacitors, transformers and ballasts to name a few.

http://en.wikipedia.org/wiki/Polychlori ... plications