Marshall JCM1H or JTM1H schematics

Tube or solid-state, this section goes to eleven!
User avatar
Matec
Information
Posts: 32
Joined: 28 Feb 2014, 11:04
Has thanked: 5 times
Been thanked: 17 times

Post by Matec »

Apparently , there is no reason that this circuit does not work. Do not worry about the fixed Bias, thus is simpler.

Do not expect a similar sound to JTM1 or JTM45. But you will have a good study amplifier.

Cheers

User avatar
mavrim
Breadboard Brother
Information
Posts: 75
Joined: 07 Feb 2015, 01:16
Has thanked: 5 times
Been thanked: 25 times

Post by mavrim »

Matec, so good to see you posting here again!

That jcm1 schematic turned out to be a fun build. Wish I had followed it from the beginning of my build, but the schematic wasn't complete then. I did find that R29 which is a 1meg resistor, should connect from V1A pin 7 to ground. It is shown as being connected between C22 and R28 to ground.

A buddy of mine actually cloned his own jcm1 and had boards made up. He sells his clone on eBay. They are built into lead 12 sized chassis and fit right into your own lead 12 combo or head. Search eBay for jcm 800 clone silver jubilee.

User avatar
mavrim
Breadboard Brother
Information
Posts: 75
Joined: 07 Feb 2015, 01:16
Has thanked: 5 times
Been thanked: 25 times

Post by mavrim »

Cloned jcm1. Search eBay
Attachments
image.jpeg

User avatar
Matec
Information
Posts: 32
Joined: 28 Feb 2014, 11:04
Has thanked: 5 times
Been thanked: 17 times

Post by Matec »

Hello mavrim.

I doubt there is a big difference between R29 connected between the ground and the V1a grid, and R29 connected between the ground and the C22-R28 node.

There will be many clones of Marshalls 1W, manufactured by talented people. This is really good. Your friend seems to be doing a great amplifier.

Cheers.

User avatar
Matec
Information
Posts: 32
Joined: 28 Feb 2014, 11:04
Has thanked: 5 times
Been thanked: 17 times

Post by Matec »

Hello everyone.

Here is a video and sample of axehack, who set up his own JTM1.

Link: [youtube][/youtube]

The description is in TDPRI Forum at this link: http://www.tdpri.com/threads/jtm-1-clone.650255/

Have fun!

Matec.

User avatar
bmxguitarsbmx
Cap Cooler
Information
Posts: 510
Joined: 25 Mar 2010, 21:15
Has thanked: 704 times
Been thanked: 216 times

Post by bmxguitarsbmx »

Fatmoocow wrote:This is a great thread. As a learning exercise I've been reworking the JTM1 to more closely match the real thing. Full disclosure I don't really know what I'm doing.

Thus far I've taken the power amp and added a long tail pair to split the signal in front of the 12au7. I'm not sure that this will work at all. In a perfect world we'd want fixed bias as well, but I don't have the skills for that.

[ Image ]

I'm going to add another 12ax7 and toss out the jubilee circuit for something that matches the JTM45 more closely.

Any feedback or ideas would be greatly appreciated.

Hey fatmoocow,
This is cool, but there may be some figuring to do first.

The classic marshall long-tailed par circuit has gain of ~ 25 (good for driving el34's)

the cathodyne phase splitter has unity gain.

The 12au7 needs much less drive to reach full power than el34's do, so a phase splitter with gain may not be helpful.

Hope that's helpful :)

User avatar
Electrochimp
Information
Posts: 1
Joined: 25 Oct 2016, 05:21

Post by Electrochimp »

What effect on the second triode plate does that 100nf and 4.7m have ? thanks

Post Reply