18Watt.com

I scored a new JTM45 offset head cab and chassis from reverb. Thought I could use it for my next 18 watt build. Started ordering faceplates, etc for a superlite and realized a JTM is not a small box chassis.

Should I get a blank chassis and get custom face plates made, save the cab for another build, or what?
I think it would be kinda fun to do my own chassis, but that's neither here nor there.

I'm afraid to find out what else I don't know about the differences in a jtm size vs small box.

Opinions appreciated.

I forgot to mention that a marshall jtm chassis, at least the one I have, has a laydown output. There's barely enough room as it is so I'd have to cover a big nasty hole.

The other option is to build a 45W Superlite TMB.

JMPGuitars wrote: ↑

Wed 10/23/24 3:44 pm

The other option is to build a 45W Superlite TMB.

That is an option. Long story, but just messing around I was goofing with my TMB MV and dimed it.
I had never done that and was completely amazed. It's all power tube distortion. That IS my new tone and that's the only way I play it. It's loud, but not hurting your ears loud. 45w would be too loud (probably)

gkwallace wrote: ↑

Thu 10/24/24 9:16 am

That is an option. Long story, but just messing around I was goofing with my TMB MV and dimed it.
I had never done that and was completely amazed. It's all power tube distortion. That IS my new tone and that's the only way I play it. It's loud, but not hurting your ears loud. 45w would be too loud (probably)

Oh, you found the magic.

Yeah, 45W would be a little louder, and less power tube distortion. You could always start with a blank chassis if you want to use that head cab.

JMPGuitars wrote: ↑

Thu 10/24/24 10:00 am

gkwallace wrote: ↑

Thu 10/24/24 9:16 am

That is an option. Long story, but just messing around I was goofing with my TMB MV and dimed it.
I had never done that and was completely amazed. It's all power tube distortion. That IS my new tone and that's the only way I play it. It's loud, but not hurting your ears loud. 45w would be too loud (probably)

Oh, you found the magic.

Yeah, 45W would be a little louder, and less power tube distortion. You could always start with a blank chassis if you want to use that head cab.

After looking at a JTM chassis layout and obtaining a file I could see that it would be easy to recreate the chassis how I want it. Just move some pieces around in illustrator and print the panels on the plotter.
I'm excited about it now.

BTW - I drilled my turret board by hand and I didn't like it. I bought new brad point bits, a new center punch and used a drill press and it still didn't come out perfect. A couple holes were out of line.

I set it up for the cnc and waiting for new stock.

gkwallace wrote: ↑

Thu 10/24/24 11:21 am

BTW - I drilled my turret board by hand and I didn't like it. I bought new brad point bits, a new center punch and used a drill press and it still didn't come out perfect. A couple holes were out of line.

I set it up for the cnc and waiting for new stock.

With your skillset, you'd never be satisfied with asymmetrical / sloppy board layouts. CNC is the right way to go.

Personally, I use my laser to mark the top of the board and then drill with the adorable Proxxon drill press, still using the guide to line up each row. If I had a CNC, I would use it.

JMPGuitars wrote: ↑

Thu 10/24/24 1:15 pm

gkwallace wrote: ↑

Thu 10/24/24 11:21 am

BTW - I drilled my turret board by hand and I didn't like it. I bought new brad point bits, a new center punch and used a drill press and it still didn't come out perfect. A couple holes were out of line.

I set it up for the cnc and waiting for new stock.

With your skillset, you'd never be satisfied with asymmetrical / sloppy board layouts. CNC is the right way to go.

Personally, I use my laser to mark the top of the board and then drill with the adorable Proxxon drill press, still using the guide to line up each row. If I had a CNC, I would use it.

A guide would have solved my problem. I was way too cocky. The ones spread apart would never show but the ones on the long edge would be ugly.

This post is with my old laser that glitched and put the name in the wrong place, but it shows my process in the images:

Very cool. That drill press is perfect.

Do you guys ever use eyelets instead of turrets? I recently had to rework a small custom turret board that I made, and the arrangement of parts required stripping most of them off in order to make changes. It was a major pita. In addition, this board was mounted vertically on the chassis next to two 9-pin sockets. Some of the parts were connected directly from socket pins directly to the turret board. Space was at a premium, and the length of the turrets (which overhung the sockets a bit) contributed to the difficulty of the job. I ended up drilling out nearly all the turrets and pressing in eyelets instead. Luckily, the eyelets I used require a slightly larger hole than the turrets, so no problem there. The end result was a design that's much easier to work with than the original. Now, if I need to replace a part for some reason, I just heat the eyelet and pull the lead out. No more unwrapping, and the leads don't get stressed when I install them. Incidentally, I use CNC to drill for the eyelets and turrets. I also use it to cut and size the boards, and have sometimes made custom terminal strips to fit available space:

Jack

Hi Jack!

It's a personal preference thing more than anything else. I prefer working on turrets 100%. I hate the look of eyelets, and I don't like the lower quality mechanical connection that allows what you're suggesting for part removal. My desoldering gun makes quick changes pretty simple, and I stopped making full wraps for most stuff. A simple J hook is all that's needed on the turrets.

However, you're the real engineer here. You know there's no meaningful difference electronically between the two options. Nobody building these amps is worrying about the minor difference in inductance between the two mounting types.

Thanks,
Josh

The thing about eyelets that’s puzzling me is how to obtain a strong mechanical connection of the second wire of a part. On a turret I solder the 1st wire on a turret and then wrap the 2nd wire half way around the other turret. You can pull that wire to strength.. how do you do this with eyelets?

Wiring to eyelets hasn't been a problem for me. The custom terminal strips in my earlier post were used in a project where several of the eyelets had three or four wires in each one. I think the usefulness depends a lot on the type of wire and components being used. Below is a photo of the turret board I mentioned earlier. This board has 16 connections in a square pattern (all but four are now eyelets). As you can see, there's no access to components mounted on the lower levels. Upper components have to be removed first, or at least one end unsoldered so they can be moved out of the way. This is part of a very complex tube hi-fi preamp project that I've been sweating over for a long time. All the circuits are finally wired and tested, but now I'm in the process of revising one section of the power supply. I'm hoping that will be the last issue to deal with before adding this to my audio system.

Jack