Identifying Input Tx leads?

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Identifying Input Tx leads?

Postby Alistair » Fri Dec 20, 2013 5:35 pm

Someone on this board has very kindly donated me some old Rola/Trimax transformers to help with my Rola 77 MKIII restoration project.

But they are completely unmarked. I tried the idiots method of hooking one up (eg, matching the coloured wires to the old coloured wires!) but it seems they've used a different colour scheme.

I've done a search on the web about identifying transformer leads, but only found hits for output transformers.
This is a can type input tranny so no obvious secondary/primary either.

Any tests I can do with a multimeter to clearly identify what's what and the ratio of the transformer?
There are 6 leads, 1 pair shows continuity (input pair?), otherwise I'm not sure what to be looking for.
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Re: Identifying Input Tx leads?

Postby Alastair Reynolds » Sat Dec 21, 2013 7:18 am

Is there a Tx model number ?
What are the colours.
If it's a locally produced transformer it should follow the standard colour code as found in the Radiotronics designers Handbook.PDF versions are downloadable.Google is your friend ;)
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Re: Identifying Input Tx leads?

Postby Alistair » Sat Dec 21, 2013 11:47 am

Hi Alastair,

No markings or codes whatsoever. Just a short black can type transformer. I believe it was from an Optro console, so I'm pretty confident it as an Australian manufacture- AWA/Rola/Trimax.

The leads are
Blue
Red
Brown
Green
Pink
Yellow

I hunted down a copy of the Radiotronics Designer Handbook, and got these colour codes for A-F transformers. Not quite sure whether there is a significance in not having a black lead and having a pink instead?
I'm a little unsure of the terms used as they seem to be things I encounter in valve amp circuits rather than mic input transformers, but at least I can identify a couple of the leads now, and have the primary and secondary clearly separated.


Blue- plate (finish) lead of primary
Red- B+ (this applies whether primary is plain or centre-trapped)
Brown- plate (start lead on CT primaries. Blue may be used if polarity is not important
Green- grid (finish) lead on secondaries (hot end of voice coil)
Black- grid return (this applied whether the secondary is plain or centre tapped)
Yellow- grid (start) lead on CT secondaries. Green may be used for this lead is polarity is not important
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Re: Identifying Input Tx leads?

Postby Alistair » Sat Dec 21, 2013 12:17 pm

And for what it's worth there is also continuity between yellow and pink leads.
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Re: Identifying Input Tx leads?

Postby Alistair » Sun Dec 29, 2013 10:45 am

Anyone have any ideas?
I also tried the method outlined here for identifying leads, but didn't get any useable numbers unfortunately.
Nothing showed any resistance, all just open (except for yellow to pink which showed very low resistance- around 2ohms)

http://www.gearslutz.com/board/geekslutz-forum/750779-anyone-know-anything-about-wiring-mic-input-transformer.html
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Re: Identifying Input Tx leads?

Postby rob » Sun Dec 29, 2013 8:53 pm

So. You are certain that only two wires show any continuity? All other wires are open circuit to any other wire?
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Re: Identifying Input Tx leads?

Postby Alistair » Tue Dec 31, 2013 10:27 am

Yep, that is what they are showing. I've got 2 of the same transformers, so I'll test the other one today incase they are different and report back.
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Re: Identifying Input Tx leads?

Postby Alistair » Tue Jan 07, 2014 12:46 pm

Sorry for a very slow response.

I tested out the other transformer, and it's responding the same. All leads showing open, except for pink to yellow. Interestingly enough, if I measure the impedance on that pair I get nothing, but if I test them on the continuity setting/diode test setting, it measures 49. I'm not sure what that is measuring though.
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Re: Identifying Input Tx leads?

Postby rob » Tue Jan 07, 2014 1:28 pm

strange....
send one over to me if you wish and i'll work it out for you

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Re: Identifying Input Tx leads?

Postby Alistair » Tue Jan 07, 2014 1:31 pm

Thanks Rob,

I tried two different multimeters just in case, but they are showing up the same on both. I'll pop one of them in the post this week.
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