Metro JTM45 PT and 1987 Lead spec?

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Big Mike
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Metro JTM45 PT and 1987 Lead spec?

Post by Big Mike » Mon Apr 08, 2013 5:47 pm

What am I looking at with SS Rectification...round 420 if I'm at 404 on the plates with a sovtek GZ34
Am I still going to get the same sort of low end WHOOMP my 50 does with George's JMP PT?

I'm just giving up on the tube recto'd thing, I"m gonna tear down, do a new board and go 71 Specs with Tesla NOS Powertubes.

Maybe Lead/Bass tone stack switch and split/shared cathode.

Thanks for the help.
Metroamp kit JMP50 - CM OT
Metroamp JTM45 turned JMP50 w/Classictone OT
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Big Mike
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Re: Metro JTM45 PT and 1987 Lead spec?

Post by Big Mike » Wed Apr 10, 2013 12:37 am

Well in case anyone is searching for the answer like I was...
I figure around 420 or so. I'll report back when I get the rest of the parts I ordered today from valvestorm and get it running.
Metroamp kit JMP50 - CM OT
Metroamp JTM45 turned JMP50 w/Classictone OT
Marshall 2550 Jubilee
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pearlrider
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Re: Metro JTM45 PT and 1987 Lead spec?

Post by pearlrider » Thu Apr 18, 2013 12:43 pm

Hi Mike,
That’s something I would like to know.
I’m building a JTM50 at the moment. I put in an order with Marstran for the transformers, 1202-118, 784-128 and a 1999 choke a few days ago. I plan after that to build a JMP lead spec. I guess I will get the answer for the question you ask when I’m finished.
Talking about plate voltage I am getting 419vdc on the plates of one of my JTM’s. I finished a JTM45 last month and I got the standard 400vdc. That was with a Ruby GZ34. (The Ruby was from my VOX ac30) At the same time I looked at the voltage on my other JTM and I got 180vdc. The GZ had gone, it was a TAD. As I needed to get a GZ34 for the amp I had just built I thought I would get a couple of JJ’s. So I sent off for two.
I put one in the older JTM and one in the new build. The new build shows 400vdc and the old build shows 419vdc. Could the age of the amp have anything to do with it? I put the old build through a punishing break in period, over twenty hours of my music collection. I did that because of something I had read on a Sozo web site. The older amp has some wallop to it now, whereas the newer amp sounds thinner. The older amp has GEC’s in it and also I live in the UK, and I’m 5 volts over at the wall. Other differences are a 100pf on the volume and a 330uf on v1. Played through a pair of 55Hrz Selestion G12H’s, it sounds thunderous, in a good way.

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Big Mike
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Re: Metro JTM45 PT and 1987 Lead spec?

Post by Big Mike » Thu Apr 18, 2013 12:57 pm

They all have the same brand and model power transformer?
Metroamp kit JMP50 - CM OT
Metroamp JTM45 turned JMP50 w/Classictone OT
Marshall 2550 Jubilee
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pearlrider
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Re: Metro JTM45 PT and 1987 Lead spec?

Post by pearlrider » Thu Apr 18, 2013 1:50 pm

Big Mike wrote:They all have the same brand and model power transformer?
The two JTM45’s have the Metro. Heyboer 1202-55.

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Big Mike
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Re: Metro JTM45 PT and 1987 Lead spec?

Post by Big Mike » Thu Apr 18, 2013 9:43 pm

Maybe earlier specs? No idea.
Mine runs at 404 with a sovtek GZ34.

I'm convrting the amp to a JMP50 though and it'll be that PT running solid state, and a classictone 50 watt El34 spec OT. -139.
Metroamp kit JMP50 - CM OT
Metroamp JTM45 turned JMP50 w/Classictone OT
Marshall 2550 Jubilee
Powered by Thorn and Kauer guitars
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Big Mike
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Re: Metro JTM45 PT and 1987 Lead spec?

Post by Big Mike » Mon Dec 01, 2014 10:48 pm

FYI getting 440 on the plates with that transformer SS rectified.
Amp is now also lead spec but closer to 68 specs.
Metroamp kit JMP50 - CM OT
Metroamp JTM45 turned JMP50 w/Classictone OT
Marshall 2550 Jubilee
Powered by Thorn and Kauer guitars
Scumback Speakers

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