JTM45 build?

bolero

bolero

Well-known member
Anyone here built a JTM45 clone before?

If so, are there any preferred layouts/circuits to use?

I have a Merren OT I ordered a while back, finally getting around to doing something with it.

Thx!

 
Metropoulos used to sell accurate JTM45 kits.  I envy you guys that can build amp without being zapped.
Were the Merren Marshall originals?

 
Another vote for the Ceriatone solutions, they can build one for you just the way you want with a choice of tone caps in he preamp if you want to nitpick.  The C-tone lineup delivers the most bang for the buck along with the real deal tone sets for their circuits, they use great parts and do not cut any corners AT ALL in their pre built boards, kits, or built for me amps, I have 3 D-clones that have the C-magic inside.  Get one built with a simple interrupt fx loop in the build, will be there if you decide to use it.

Blah blah blah ,

take my word for it please,

saving you key spew...

mine do all sound amazing.

Research JTM 45, earliest ones ran 5881's through a not for guitar amp OT, the Radiospares.  Mercury Magnetics builds the Radiospares type in various configurations.  I have one of those Mercury 'Spares enhanced OT's in my Siegmund Blues Breaker JTM45 head with parallel tube fx loop.  That amp is king of the tone pile of all my amps including the D-clones with some real Tung Sol 5881's going into that enhanced 'Spares tranny with the 8.8k primary selected.  Besides the original, unicorn fx loop, that OT is a very big part of the reason why the Siggy sings like the fat lady closing out the show at the opera.  Nik at C-tone will say that his locally sourced at his spec OT iron for his JTM45 build is just as good as anyones, period, and he won't be way off at all.  His D-clone stuff has proven it for me.

 
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Thanks all!

I doubt I'll order a kit: just get the parts & build it. Thx for the tip on Ceriatone docs, I forgot about them. I had a Ceriatone DC30 & it was a fantastic amp.

Chris Merren hand builds his own transformers & is a longtime specialist on old Marshalls. He used to work for NASA & really knows his stuff. He also makes Neve, McIntosh, and Hiwatt replacement transformers:

http://merrenaudio.com/marshall_output_transformers

I have one of his OT's in my '66 JTM100 and it's amazing. So I bought a JTM45 OT with intent to build one, at some point.

 
I’m starting a JTM45 build this weekend. I’m going with a KT66 version. I’m using a Mercury Magnetics 8 ohm Radiospares ot and a Hammond 273Bx pt. I will have enough amps to run EL34 if I want to and the ot has the ability to go that route too as well as 6l6 tubes. I have a Hammond aluminum chassis for the build. I’m going to roughly follow the layout for the Bassman but I’ll have the electrolytics on the board inside instead of external or with cap cans like the Fender or Marshall’s.  I’m also going to set up a bias with individual adjustment for the KT66s so I can have them out of balance or exactly perfect, whatever sounds best. I’ll put two bright caps on the bright channel too, 100 and 4700pf. The 4700 will have a 220-470k resistor in series so it’s more of a mid boost and not quite as powerful. I did it on a 6g3 I built and love it. Without the resistor it is too overpowering. I’ll experiment with the value between 220-470k to see which I like the most. I used a 470k on the 6g3. 

 
Awesome!

I think aluminium is the way to go.

I had a Ceriatone JTM45, it sounded good. Wish I hadn't sold it, which is why I want to build another. Life is getting in the way though.

 
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I finished my build and it is the fourth amp I’ve built and just replaced the 6g3 as my favorite amp. The 45/Bassman is just a timeless design and sounds good no mater what it’s amplifying. The 6g3 does too but when I turn the guitar volume down the 45 just has a cleaner more beautiful sound. I ended up with a 250pf/off/4700pf with a 270k series resistor bright switch. I think I’ll change to a 470k resistor to take the highs down another 1k hz to focus the mids more. With the volume down the 250PF sounds nice with the neck pickup. I also put a negative feedback switch that goes from Bassman/off/45 and it is one of my favorite things on any amp. It really makes a versatile amp. I have not put a ay7 in v1 yet but I think it will sound great that way too. I made the normal channel with. 100k plate resistor 1.5K bias and the bright side with a 220k and 2.7k bias so it’s a little more Marshall on the bright side than a 45 was. The amp is LOUD so it will have limited giging. I would like to make a mini version with 6k6 tubes and a single input at some point. 

 
Also, I used a tone stack from the Blackface era but with a 56K slope resistor, it’s more chimney. Mainly it is a .1 cap vs a .02 on the bass side of the treble pot. It’s Fender’s secret sauce. 

 
I’ll get some picture up tomorrow. I just got back from a glacier and I have some pesky blisters on my big toes. 

 
The cab is ugly and is made from a table I recycled into a box as a housing. 
Gut shot

IMG_4502.jpeg

Back, on/off and 8 ohm outs

IMG_4503.jpeg

Front, Bassman/JTM hi low inputs, vol 1, vol 2, TMB and Pres. Top switch is a 220ph treble/off/4700ph270r mid boost. Bottom switch is B/off/J neg feedback. 
IMG_4504.jpeg

Playing through 4 Weber DT-10s in a recycled pine cab. 
IMG_4506.jpeg

I roll up and down the volume in these vids on the pickup settings. I used my phone so it’s not that great and sounds a little more distorted than it actually is at the lower volumes. The full volumes are more correct in the way they sound. The guitar is plugged straight into the amp and the tone knobs are set to full on the guitar. The V is 50%, T is 50%, M 50%, B 35% and P 65%. 



 
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