JTM 45 Head Cab Plans

[stickyfinger]

I'm finally starting to build a Split Top JTM 45 and will be doing the head cab myself butt jointed like the originals (only cause its easier). I had cut 12mm / 1/2" baltic birtch ply maybe 5 years ago for the shell and I'm questioning if 1/2" is the correct thickness?? I only have a 72 large box JMP to use as reference.

I know the old Marshall catalog showed the head shell size as 26"x 9x 8"1/4".
This is 9" high not including feet?
Thickness of wood, shell, front and rear panels?
Control panel cut out size?
Tad pole string distance from end?
Size of the (pine?) cleats?
Round over 1/2"?

Really any info would be appreciated.

 

[paul-e-mann]

I'm finally starting to build a Split Top JTM 45 and will be doing the head cab myself butt jointed like the originals (only cause its easier). I had cut 12mm / 1/2" baltic birtch ply maybe 5 years ago for the shell and I'm questioning if 1/2" is the correct thickness?? I only have a 72 large box JMP to use as reference.

I know the old Marshall catalog showed the head shell size as 26"x 9x 8"1/4".
This is 9" high not including feet?
Thickness of wood, shell, front and rear panels?
Control panel cut out size?
Tad pole string distance from end?
Size of the (pine?) cleats?
Round over 1/2"?

Really any info would be appreciated.

What's split top mean?

 

[Geeze]

Have you moved forward with this build?

I've seen recently on the JMPs Marshall ran 15mm on the shell, 12mm on the front and 10mm on the rear.

Russ

 

[stickyfinger]

Nope havent touched the head cab. Still unsure, Will look like this but with a silver face plate. Looks like 12mm for the shell to me.

https://reverb.com/item/82944440-vintage-1964-marshall-jtm45-mkii-bass-white-split-front-metal-badge-amplifier

 

[neikeel]

I’ve just measured three cabs (64 split front, 65 block and 65 script) all are 12mm top, bottom, sides and front. Approx 9mm (10 with levant) rear. The earlier two definitely butt jointed (as is 65 script logo 45/100). Can’t tell on the later 65 script logo JTM45.

 

[stickyfinger]

I’ve just measured three cabs (64 split front, 65 block and 65 script) all are 12mm top, bottom, sides and front. Approx 9mm (10 with levant) rear. The earlier two definitely butt jointed (as is 65 script logo 45/100). Can’t tell on the later 65 script logo JTM45.

Does the 64 split have a thin metal front panel and no rear panel?

 

[neikeel]

Does the 64 split have a thin metal front panel and no rear panel?

Yes it does, with pitched front knobs, RS Deluxe OT and RS choke. PT is odd one, still RS selector on top but not self lead and subtly different to both the 65s (one has RS OT and choke, the other selector on side Drake and -114 choke).

 

[coffeecupman]

Am I the only one reading this who thinks there's no such thing as too many pictures?...

 

[Marcomel79]

Yeah, where the pics at?

 

[neikeel]

The 64 isn't mine and likely be up for sale soon, I've posted pics of my 65 and old 64 (smooth vinyl, silver maroon logo) and my split front clone before.

 

[neikeel]

If you need pics I can pm

 

[william vogel]

12 mm Baltic birch for the sides, top bottom and front panel. 8 mm rear panel. 3/4 inch round over. I’ve made “plates” that insert into the front and rear panel openings that prevent me from running over with the bearing on the bit to shape the front and back properly because the 3/4 inch radius is past the thickness of the 12mm boards. I cannot remember the inset measurements for the string grooves. The front panel is cut 1/4-3/8 smaller than the opening to allow for the tolex and the piping. The rear panel is cut 1/8 to 3/16 smaller for the tolex. I cut the string grooves a depth of 0.140 and the width is 0.100 (saw blade width). I cut all the tolex into separate pieces and insure 0.140 overlap into the grooves so the tolex is completely captured by the string. Many don’t do this and the shrinkage of the tolex will pull out with only a single wraparound and cut. Don’t do it, cut every piece that spans sides top and front to imbed the tolex. The corners are meticulously cut and require quite a bit of patience and experience. Once you’ve mastered the corner cuts and fit, you’re a master. DONT STRETCH the tolex. It will shrink and open and the corners will become crappy within six months. I’ve built over 50 cabinets and the tolex still stresses me out. The Marshall cabinet IS the most beautiful work I’ve seen for tolex covered cabinets. The string design to capture the tolex ends is brilliant and accents the look.

 

[stickyfinger]

12 mm Baltic birch for the sides, top bottom and front panel. 8 mm rear panel. 3/4 inch round over. I’ve made “plates” that insert into the front and rear panel openings that prevent me from running over with the bearing on the bit to shape the front and back properly because the 3/4 inch radius is past the thickness of the 12mm boards. I cannot remember the inset measurements for the string grooves. The front panel is cut 1/4-3/8 smaller than the opening to allow for the tolex and the piping. The rear panel is cut 1/8 to 3/16 smaller for the tolex. I cut the string grooves a depth of 0.140 and the width is 0.100 (saw blade width). I cut all the tolex into separate pieces and insure 0.140 overlap into the grooves so the tolex is completely captured by the string. Many don’t do this and the shrinkage of the tolex will pull out with only a single wraparound and cut. Don’t do it, cut every piece that spans sides top and front to imbed the tolex. The corners are meticulously cut and require quite a bit of patience and experience. Once you’ve mastered the corner cuts and fit, you’re a master. DONT STRETCH the tolex. It will shrink and open and the corners will become crappy within six months. I’ve built over 50 cabinets and the tolex still stresses me out. The Marshall cabinet IS the most beautiful work I’ve seen for tolex covered cabinets. The string design to capture the tolex ends is brilliant and accents the look.

I’ve done 5 cabs so far and probably only 2 were good enough. I’ll definitely use the tips provided.
The early jtm 45s were a bit different in roundover (likely 1/2”) and string location probably other details all so compared to the more traditional plexi cab.

 

[stickyfinger]

Yes it does, with pitched front knobs, RS Deluxe OT and RS choke. PT is odd one, still RS selector on top but not self lead and subtly different to both the 65s (one has RS OT and choke, the other selector on side Drake and -114 choke).

Hey Neil if you get a free chance this week can you give me some more measurements of the cab?

Most important-

26"x 9x 8"1/4" This is 9" high not including feet?
Control panel cut out size? Width and height.
Tad pole string distance from end?
Least important-

Chassis 6" 3/4" wide?
Size of the (pine?) cleats?
Round over 1/2"?

Saturday I plan on pulling out the tools and building this cab! I think I've been collecting for this amp since 2016 lol. Been a long time and folding a thin aluminum chassis like the original. Should be a spectacular build!