Metro JTM45 PT suitable for JMP50?

shakti · Post by **shakti** » Fri Nov 02, 2007 12:41 pm

I built a Metro JTM45 with the stock PT. The amp sounds *great*, but I've been considering changing the PT to one which delivers a little more juice. The B+ is roughly 400VDC whereas the original JTM45s were usually running closer to 450.

However, I am also planning to build a JMP50, and with solid state rectification I am guessing the JTM45 PT will put out closer to 420-430VDC? Will the PT work for this purpose?

George - how different is your JTM45 from the JMP50 one?

Alternatively, I might transform my current JTM45 into a JTM50 and recycle the OT for a future Bluesbreaker build...this way I might end up with both JTM45 Bluesbreaker, a JTM50, and a JMP50!

shakti · Post by **shakti** » Fri Nov 02, 2007 1:32 pm

And if I want to transform my JTM45 into a JTM50, does anyone know where I can get...

- a matching faceplate

- a 1202-128 OT replica?

Flames1950 · Post by **Flames1950** » Fri Nov 02, 2007 6:21 pm

Do you mean a 784-128 transformer? Brian Wallace has them made.

shakti · Post by **shakti** » Fri Nov 02, 2007 6:56 pm

Oops, yes, that's what I meant. And yes, now I see it. I was only looking at the page for his JMP 50 OT, but on the page of currently available transformers, he has it listed. Veeery interesting.

What else will I have to do to turn this into a JTM50? Obviously change to 1k screen grid(?) resistors to use EL34, and re-bias. Should I change the mixer resistors to 470k?

Has anyone built a JTM45 with "proper" panels? I am aware that some amps came out with JTM45 faceplates yet EL34 tubes, but it seems the majority had the black flag/reverse JTM lettering. Did Marshall ever put out any of these amps with a proper "JTM50" panel with that lettering on the right side of the panel, just like the JTM45?

bluze81 · Post by **bluze81** » Fri Nov 02, 2007 7:22 pm

I have never seen a Marshall amp that said JTM50 on the fromt panel? perhaps they did have it? I would love to have a reverse black flag JTM logo on my clone I am building but think its a trademarked logo and could be trouble,somebody would have done it,anyone else care to chime in here?

Post by **Scumback Speakers** » Fri Nov 02, 2007 7:58 pm

What's the answer to the question about using the JTM 45 PT for 50 watt Plexi? I just realized I have two Mercury Magnetics JTM 45 PT's and would be happy to use one of them instead of ordering another one from MM.

Roe · Post by **Roe** » Sat Nov 03, 2007 3:00 pm

you need to up the filtering to 32 throughout