Marshall JTM 45/50 or BB Combo?

[Decko]

Hi All,

Just picked up this Marshall aluminum chassis and boards (preamp board and power board) from a guy who started a build but did not finish. Looks like a Marshall JTM45 50.

As I was dissecting the JTM45 50 schematic, I noticed that the physical layout shows one board! Not two boards as what I have.

More research show that the JTM100 uses two boards and not the JTM 45 50.

That said, I am not sure what I have here. Could be a custom jobber.

Can you help clarify (based on the pictures below) if there is indeed a Marshall JTM45 50 with two boards? or is this a different model?

Thanks!

[ToneMerc]

There's a JTM50, no such model as a JTM 45 50. The JTM50 is a single board like JTM 45 with either a S/S or GZ34 rectifier. The cap board appears to be setup for axial caps instead of using two cap cans. Some of the Weber kits use two boards, with a cap board instead of cap cans. It cannot be a BB because there's not enough pot holes. The person you purchased this from should have some idea of what he sold you.

JTM50

http://marstran.com/67%2010054.htm

TM

[M Fowler]

Here is the Weber 45 chassis drawings to compare with.

[Homebelly]

seems like that chassis is quite big for a JTM45 to JTM50.
At least it does when compared to the boards, assuming the boards are the usual size...

I'm wondering if this couldn't be made into a JTM45/100 by cutting one more hole..

[ToneMerc]

seems like that chassis is quite big for a JTM45 to JTM50.
At least it does when compared to the boards, assuming the boards are the usual size...

I'm wondering if this couldn't be made into a JTM45/100 by cutting one more hole..

It looks like the Weber chassis, what's thrown off is that the cutout is for a Bassman which makes the interior looks larger than what it appears to be. You would have to enlarge the cutout and I would be leary of mounting a 17lb JTM45/100 PT in that pop riveted chassis.

TM

[Roe]

Hi All,

Just picked up this Marshall aluminum chassis and boards (preamp board and power board) from a guy who started a build but did not finish. Looks like a Marshall JTM45 50.

As I was dissecting the JTM45 50 schematic, I noticed that the physical layout shows one board! Not two boards as what I have.

More research show that the JTM100 uses two boards and not the JTM 45 50.

That said, I am not sure what I have here. Could be a custom jobber.

Can you help clarify (based on the pictures below) if there is indeed a Marshall JTM45 50 with two boards? or is this a different model?

Thanks!

basically you have a jtm45 style chassis (also used on the very first 50w amps although marshalls had holes both for a filtercap and gz34 on top on both 45s and early 50s). the boards looks like something based on an early plexi 100w. the preamp board is the same for 45s, 50s and 100s. you dont need the power board for a 45/50w. for references check metroamp, ceriatone, amparchives

[Decko]

Hey Folks,

Thanks for the feedback. Based on your comments and some thought, I will build the JTM50 using EL34's over Kt66's/6L6's.

The chassis is not the Weber based on the dims. I guess it is a custom job. Nonetheless it is nice and thick with a polished top surface.

In addition, I will continue with the spirit of the existing layout and populate the power cap board.

Should be a fun project!

Regards,
Decko

[M Fowler]

Decko,

Yeah it looks like a good chassis.

I like the EL34 version better myself and used the 3k4 OT.

The JTM45 plus is a good circuit http://tubedepot.com/kit-jtm45plus-combo.html see instructions on bottom of page

[Decko]

Decko,

Yeah it looks like a good chassis.

I like the EL34 version better myself and used the 3k4 OT.

The JTM45 plus is a good circuit http://tubedepot.com/kit-jtm45plus-combo.html see instructions on bottom of page

What is the differentiating feature of the "plus" version? Switchable rectification?

Decko

[Homebelly]

Decko,

Yeah it looks like a good chassis.

I like the EL34 version better myself and used the 3k4 OT.

The JTM45 plus is a good circuit http://tubedepot.com/kit-jtm45plus-combo.html see instructions on bottom of page

What is the differentiating feature of the "plus" version? Switchable rectification?

Decko

It also seems to have a variable or switchable NFB circuit and a master volume.

[statorvane]

The voltage rail filtering resembles a 50 more than a 45. There is also a switch able tone stack - either a 45/50 or JMP50 (lead). So it's a real chameleon - not necessarily a bad thing.

[M Fowler]

I just think for those of us that want more than a JTM45 with KT66 tubes there are quite a few different options out there for us to build.

I have to say my favorite is the mojotone JTM45 that uses EL34's and OT 3k4