Identifying orange wire pair on Merren JTM45 PT

[stevehollx]

I ordered a JTM45 PT from Merren, and it didn’t come with a wiring diagram.

I found a diagram somewhere else, but I am unsure what the orange pair is (labeled ‘P’, likely cut off) on the diagrams left wires. What is that for? Primary hookups on the lower right lugs and tap wires, 6.3V heaters on the upper rights, 5V for rectifier power on the lower left lugs, and the LV and HV taps on the upper left lugs.

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[martin manning]

You could always ask Merren, but if you want to investigate yourself, start by finding out if the orange wires have continuity from one to the other and to any of the other terminals. If they only have continuity to each other, it's a separate winding. That would be my guess. Then, put 12 VAC on the 120 VAC primary and check all the other terminals to see if you get 1/10 of the expected voltage. Measure the voltage on the orange wires, which will help you figure out what they are for. Might be a second 6.3 VAC winding.

[stevehollx]

After more research I’m pretty sure it is a 300v tap. I asked for a Variac switch type tap when he built it and figured it would be the inter lugs on the HV tap. But based on documentation that looks to be 425/450 so the 300v must be the orange pair for the variac style dropped voltage tap.

I’ll validate by putting 12v through it.