Metropoulos Forum

I am starting a JTM45 build with a MM Radiospares OT tomorrow. I want to make sure I understand the speaker jack wiring, so as not to accidentally blow my OT. I want to wire it for 16 ohms.

My brown & white leads off the OT secondary connect to the speaker jack like in this picture I have found (brown and red in the picture), and my NFB lead attaches to the other side of the same jack. And then I need to add a ground ground to the jack. And red & black are soldered together, as are blue & green. Is it important which lead goes to the front & which goes to the back of the jack? Thank you!

Missing anything? This OT is new to me. Thanks!

Yes it is important

The ground wire is negative (usually to an output valve base ground) goes to the nearest lug to the chassis - that is the sleeve of the jack, the common of the OT secondary is also to this lug and on the MM OT is the white wire.

The tip of the jack is positive, ie hot. If you are going for 16ohms then, the brown wire goes to the tip.

The other wires blue to green and red to black pairs are soldered to each other and shrink wrapped under the board.

The NFB (purple wire) is best soldered to the jack tip for 16ohms NFB

Thank you, Neil!

Trying to decide if I should hook up the 6.6K or 8K. Any thoughts?

Also I am think now about 8 ohms given my speaker situation. It looks like I solder the red and blue wires together and then run a lead off of that?