Using different spec trannies in Metro JTM45 circuit

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JMT
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Using different spec trannies in Metro JTM45 circuit

Post by JMT » Fri Nov 09, 2018 6:53 pm

Dear experienced JTM45 DIY builders,

I am doing my first amp build using Webber quality kit components and transformers of Chinese origin (I'm on a budget and postage down under is prohibitive). The kit is based on the 1987 JTM45 circuit but handwired so basically includes all the components of the various JTM45 kits available. As I have read and heard such great reviews of the Metro JTM45 I was hoping to build a more vintage Metro style JTM45 circuit. As my electronics theory is lagging I wanted to ask how critical the specs of the trannies and choke are if I wanted to do a Metropolous JTM45 build based on the 2008 PDF instructions?

The PT has slightly higher voltage on the high voltage wires, 350V vs 323V for the MM PT in the Metro kit and the biggest difference is the current on the 6V wires is 3.5A (not 6A) and the 5V wires is 3A (not 5A). Will this be a major issue and prevent from using the Metro circuit? Also the OT has a primary impedance of 4.2k and the choke is rated at 5-8Hy and 200mA.

Thanks a lot

JMT

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axeman
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Re: Using different spec trannies in Metro JTM45 circuit

Post by axeman » Tue Nov 13, 2018 7:28 pm

I don't see much of a problem, but if you are building a JTM45 amp do it right the first time. A JTM circuit is the same as a 1986 circuit "bass amp" with referent PT and OT, If you are looking to save many do it with the components. Buy Orange drops for the coupling caps and use Xicon resistors. Don't lay cheap on the PT and OT. 1987 is a lead circuit

JMT
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Re: Using different spec trannies in Metro JTM45 circuit

Post by JMT » Wed Nov 14, 2018 5:00 am

Ok thanks, my understanding is 4.2k ohm vs 8k ohm primary impedance for the metro OT is an important difference and possibly impedance mismatch would need to be wired on the OT resistance selector. Anyway I have linked the 2010 JTM45 Ceriatone circuit provided with the kit which I will use, just wish I could afford those Mercury Magnetics transformers to do a Metro build. Cheers from down under

https://music-electronics-forum.com/sho ... php?t=2205

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axeman
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Re: Using different spec trannies in Metro JTM45 circuit

Post by axeman » Wed Nov 14, 2018 11:36 pm

You do not have use Mercury Transformers, they are a little to bright for me go with Heyboer or Hammond Transformers.
https://www.heyboertransformers.com

https://www.youtube.com/watch?v=yH2PoFSUObI

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