Jtm45 metroamp and Mercury OT wiring

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Tcaradonna
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Jtm45 metroamp and Mercury OT wiring

Post by Tcaradonna » Sat Mar 02, 2019 6:40 pm

I have a Mercury Magentics output transformer, O45JT-16.
It has red, black and brown wires from the primary.

The metroamp instructions call this the optional tranformer. However the instructions for wiring are anything but clear. The instructions say, wire the black to pin 3 on the left sock and red to pin 3 on the right.

Huh? Which is the left and right?

Can someone who has used this transformer chime in and tell me which is which?
Thank you!

danman
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Re: Jtm45 metroamp and Mercury OT wiring

Post by danman » Sat Mar 02, 2019 7:35 pm

It really does not matter. The OT"s primary is just a coil with a wire at each end and a centertap that connects to B+ voltage. In any build that has a negative feedback circuit (most Marshalls do), you have a 50/50 chance of connecting the proper wire to each socket. If you get it right the first time, the amp sounds great. If you get it backwards, the amp usually squeals or howls when you first turn it on and flick the standby switch. Most builders will leave these wires a little long until after the first startup in case they need to swap them around. Just be sure that you locate the proper wire as the centertap and connect that one to the B+ voltage.

Tcaradonna
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Re: Jtm45 metroamp and Mercury OT wiring

Post by Tcaradonna » Sat Mar 02, 2019 7:55 pm

Thank you. I’ve seen that advice elsewhere too, as others have posed the same question and there hasn’t been a definitive answer that I can find. I know the center tap is brown.

I have seen 3 examples I’ve found on the web that appear to be wired with black going to v5, red to v4. (Opposite of what metroamp suggests if their left/right specificity refers to the picture on the same page). I’m going to wire it as the examples seem to show (rather than instructions as others have eluded to being incorrect) to start and prepare for fireworks on ignition. Just kidding. I’m leaving the leads long enough to change if need be.

The visuals...
https://ibb.co/wSVpMTD
https://ibb.co/SQKVRDC

Cheers.

danman
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Re: Jtm45 metroamp and Mercury OT wiring

Post by danman » Sun Mar 03, 2019 7:25 pm

Sometimes the left and right colors can be different on two of the same OT's so it never hurts to leave them long until after the first start up. Amps without nfb don't have this issue so you can switch the wires around without concern. If by chance the primary wires are trimmed to short to swap, you can also switch the pin 5 leads coming from the phase inverter tube

Tcaradonna
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Re: Jtm45 metroamp and Mercury OT wiring

Post by Tcaradonna » Tue Mar 05, 2019 10:57 pm

Mercury confirms that the OT has maintains consistent color conventions for windings and tap leads. But they also suggest wiring with excess leads and flipping/trimming excesss after power up. Hopefully I can post what is definitively the right way for the Metropoulos build.

Tcaradonna
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Re: Jtm45 metroamp and Mercury OT wiring

Post by Tcaradonna » Wed Mar 13, 2019 12:25 am

To any other builders using a Mercury OT with the MetroAmp/Valvestorm JTM45, the primary wiring hook up is:
Red to V4 pin 3
Black to V5 pin 4
This is consistent with other Mercury JTM45 examples I have seen on the web, and should be the correct wiring for all future Metroamp/valvesform JTM45’s using Mercury OT. Mercury says they will never change the wire color convention.
I hope this helps someone!

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