Help With OT!! - Secondary tap identification - extra wire??

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ESR
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Help With OT!! - Secondary tap identification - extra wire??

Post by ESR » Thu Nov 04, 2021 2:56 pm

I could really use some help with something here...

I'm doing a JTM 45 build for a friend. He supplied me the transformers he wants to use, including a Classic Tone/Magnetic Components output transformer. I tried to attach picture to this post, but each time I try to attach a picture, I get an error message that says "sorry, the board attachment quota has been reached"... I guess that means the board can't handle any more attachments...? Anyway, I'll do my best to describe my issue.

The Magnetic Components OT here is the "40-18025", which you can find online as the proper OT for a JTM45 build.

The spec sheet for the OT online shows four taps coming off the secondary:
Black--common
Yellow--4ohm
Orange--8ohm
Violet--16ohm

But the actual wires coming off the secondary side of the transformer in my hand are:
Black--common, I assume
Yellow
Green
White
Gray

(The primary side has red, blue, brown, and I'm already confident which lead is for what on the primary side.)

From an unclear picture I have from the friend of this transformer in an amp before, I'm fairly confident that the yellow tap is 4ohm, green tap is 8ohm, and white tap is 16ohm... but I can't figure out what the gray wire would be for.

Any help is much appreciated!!

ESR
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Re: Help With OT!! - Secondary tap identification - extra wire??

Post by ESR » Thu Nov 04, 2021 3:44 pm

Ok, I've actually figured out that the yellow is the 16ohm tap, green is the 8ohm tap, and white is the 4ohm tap... Black must be common... That leaves the gray wire... Any idea what this could be?

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neikeel
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Re: Help With OT!! - Secondary tap identification - extra wire??

Post by neikeel » Tue Nov 09, 2021 4:28 pm

If you have four secondary taps often the 'spare' is a 100v winding for PA use

Normally on these

Brown - common
Black -4
Yellow -8
Green -16

White 100v

I guess you don't have a variac to put 100v through the primaries and do a turns ratio calculation?
Neil

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