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Transformer help

H

hammeredklavier

owner of two very cheap hi-fis
... and another one please chaps:

https://photos.app.goo.gl/kTJgXG6E55qUR6J87

Again, sorry I can't embed the image. This is out of Les's sin bin, no idea where he had it from! Presumably a monoblock.

So, brown and blue are obvious.

Green is zero (centre tap), white and yellow are positive?

The smaller red and black wires? Presumably a smaller secondary? Measures 1.2 ohms, versus 0.3 ohms green-yellow and green-white, 0.5 ohms white-yellow. (I can't zero out the leads with the meter I've got to hand, so I'm guessing it's ~0.2 ohms positive to zero, ~0.4 ohms positive to positive, hence I'm presuming green is zero.)

Sorry if I'm being a dunce, I'm a bit rusty to say the least!
 
No "positive" as such as AC but yeah all sounds correct otherwise. Twin secondaries but wired together obviously. Looks like has twin 115V primaries wired to give 230V and then brown and blue tails added.

Secondary voltages? >Put mains to primary and measure it. VA? Size and weight give a near enough idea but without being there...
 
Arkless Electronics said:
No "positive" as such as AC but yeah all sounds correct otherwise. Twin secondaries but wired together obviously. Looks like has twin 115V primaries wired to give 230V and then brown and blue tails added.

Secondary voltages? >Put mains to primary and measure it. VA? Size and weight give a near enough idea but without being there...
Click to expand...
Yeah, you know what I mean ;-)

I think Les said 450 VA, I've had it a few months and lord knows how long it'd been kicking around Avondale Towers...!

Right, OK, I don't understand what the red and black wires are for? Feel free to laugh at me! :-D

Ta

Alex
 
Check the red and black have no connection to any of the other windings (unlikely) and then as you surmise it's another secondary winding... You'll need to measure the voltage same way as the main windings.

it's "for" anything you want at the voltage it gives..... or don't use it. Its original intended use is irrelevant but something like panel lighting, speaker protection etc
 
Arkless Electronics said:
Check the red and black have no connection to any of the other windings (unlikely) and then as you surmise it's another secondary winding... You'll need to measure the voltage same way as the main windings.

it's "for" anything you want at the voltage it gives..... or don't use it. Its original intended use is irrelevant but something like panel lighting, speaker protection etc
Click to expand...
Thanks Arkless. Yeah it's another little secondary, I just wondered if there was an obvious purpose for it... it'd be interesting to know where the transformer came from!

And thanks again for assisting. I've had this stuff sitting on a shelf for a few months now and I'm only just starting to have a proper look at it and see what's to be done. It'd been on my mind for a while that the transformer seemed to have rather a lot of wires coming out of it and that the colours - apart from the obvious ones - didn't tell me much, but I only got round to taking a meter to it yesterday!

I'm sure there'll be more once I get building, meantime many thanks.

Alex :)
 
That is a very "handy" Stereo amp transformer; twin 110V primaries, allowing use in UK or USA (by putting the primaries in series of parallel), two separate centre-tapped secondaries giving plus and minus rails, and (likely) some kind of low power output for softstart and/or speaker protection circuitry.

It's enough for anything shy of a Voyager (2 PSUs per output) configuration.
 
bugbear said:
If you can jury rig a current source, you could improvise a milli-ohm meter, using a 4 wire connection. Even a bad 4 wire connection ohm-meter is a lot better than a multimeter!
Click to expand...
I've got a Fluke 1507 which'll at least zero properly, but I don't always have it on me... good tool but not required every day!
 
Right, something has just occurred to me that I hadn't considered before: do I need a soft start or shouldn't I worry about it? 450 VA isn't massive in the grand scheme of things.

Thoughts? If a case fuse blows every year or so then never mind, but if it's going to make a habit of it...!

Ta
 
Should be OK without one. My NCC uses a pair of 250VA transformers so 500VA total. I originally fitted it with a T2.5A fuse which blew after about 10 switch cycles. Fitted a T3.15A and has been fine ever since. If you have room and your spare secondary is suitable, I'd fit a speaker protection module. Never fitted one myself though.
Edit: If you go by ESP (Rod Elliott) 500VA is about the upper limit above which you need slow start.
 
a.palfreyman said:
Should be OK without one. My NCC uses a pair of 250VA transformers so 500VA total. I originally fitted it with a T2.5A fuse which blew after about 10 switch cycles. Fitted a T3.15A and has been fine ever since. If you have room and your spare secondary is suitable, I'd fit a speaker protection module. Never fitted one myself though.
Click to expand...
Yes, I'll get the transformer connected up ASAP and see what the voltage is on the mystery secondary coil. Speaker protection would be nice.

Any suggestions? I think Les Avondale makes one now doesn't he?
 
Yes, I believe he does, but not certain TBH as I don't use one... Just be careful bu99ering about with the mains! It can definitely bite (I've had a couple off it) and can kill.
 
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