Finally Building JTM45: Stupid Questions As They Arise

[The New Steve H]

We were putting the trannies in today, and it turns out a Classictone JTM45 power transformer will not fit the screw holes in a Mojo chassis. This is pretty annoying.

The original holes are so close, it would be difficult to add new holes without ruining the existing ones and ending up with a mess.

I'm thinking I may machine an aluminum spacer, but I thought I should ask: is there a clever and easy solution which other people already know about?

This is a transformer that lies on its side.

[NickC]

We were putting the trannies in today, and it turns out a Classictone JTM45 power transformer will not fit the screw holes in a Mojo chassis. This is pretty annoying.

The original holes are so close, it would be difficult to add new holes without ruining the existing ones and ending up with a mess.

I'm thinking I may machine an aluminum spacer, but I thought I should ask: is there a clever and easy solution which other people already know about?

This is a transformer that lies on its side.

I used a Mercury Magnetics JTM45 Toneclone PT. It also did not line up with the pre-drilled holes in the aluminum chassis. I drilled holes where they needed to be, and mounted it in stand-up position. As an added bonus, got some more real-estate inside the chassis for the can caps.

If you go that route, make sure you orient the transformer cores/lamination of the PT and OT properly (i.e. not pointed the same way).

[ToneMerc]

We were putting the trannies in today, and it turns out a Classictone JTM45 power transformer will not fit the screw holes in a Mojo chassis. This is pretty annoying.

Yep, that's what happens when the vendor(Mojo) doesn't have a real clue on the amp in question. The JTM45 laydown PT has the same cutout/mounting center pattern as the Fender Twin PT, which is 3 x 3.75.

What I would do is redrill the chassis holes and use the "english" PT bracket. The bracket will cover the old holes on the inside and the PT lamination stack should cover the old holes on the outside as well. I get the brackets directly from Heyboer, but Mercury I believe has started to sell them as well. I'll look when I get home, I might have an extra that I can part with.



TM

[The New Steve H]

Redrilling the holes will cause some problems. Having looked it over, we have two solutions which might be easier. One is Nick's idea. The other is to take a piece of aluminum and fix it so the transformer attaches to it. The other side will attach to the chassis. The transformer will be about 7/16" higher than originally designed, but it will still be lower than the tubes.

I might have to replace the screws running through the transformer with shorter ones. That might be no fun, given that they're covered with some kind of hardened snot.

[ToneMerc]

Redrilling the holes will cause some problems. Having looked it over, we have two solutions which might be easier. One is Nick's idea. The other is to take a piece of aluminum and fix it so the transformer attaches to it. The other side will attach to the chassis. The transformer will be about 7/16" higher than originally designed, but it will still be lower than the tubes.

I might have to replace the screws running through the transformer with shorter ones. That might be no fun, given that they're covered with some kind of hardened snot.

Steve here's a lesson I learned from building both firearms and engines. I find it applies to amp assembly as well, mock up parts fitment before you start final assembly.

TM

[The New Steve H]

That is good advice. Of course, we couldn't do that before ordering.

[M Fowler]

it turns out a Classictone JTM45 power transformer will not fit the screw holes in a Mojo chassis.

Steve, I found this out as well and drilled out the chassis then to find out that this chassis does not work for KT66 JTM45 only EL34 JTM50.

I had a set of mojo JTM45 transformers so used those instead.

The Triode JTM45 chassis is setup for KT66 and will accept the mojo JTM45 faceplate.

Mark

[The New Steve H]

Wait...they sold this guy a JTM45 chassis that won't accept JTM45 guts? Are you serious? What's the problem? We can't send the chassis back, because it has already been marred a little.

[Reeltarded]

If I'm honest, Mojo really only exists because something else doesn't. I am scared by my experience with every order I ever made with them, from poor quality parts in some instances, to kits no one can unfurl.

Weber acts like Mojo too.

I stopped using the word 'mojo' as a descriptive after my first experience with them. Who's bad? Michael Jackson.. Take that as it is.

I predict Mark will say the output tubes are too close together for most real fat tubes. El34s work though.

[ToneMerc]

Guys, just an FYI here's the faceplate drill pattern for the JMP/Plexi which is not the same as a JTM45. More than once I've seen vendors sell a JTM45 chassis that will not accept a true JTM45 faceplate.

TM

[M Fowler]

There is not enough room on a mojo JTM45 chassis to use the Triode PT which is a lot larger. This affects the OT placement and choke placement as well as room for KT66 tubes.

Mojo openly advertises their kit as 3k4 OT for use with EL34s my first clue. The board layout and physical layout in a mojo is different.

Makes for a great sounding amp though.

My intention was to build both a Triode KT66 version JTM45 and Mojo JTM45/50 EL34 version both are good.

Mark

[jelle]

Metro is selling the Jtm45 chassis and panels again. What is the verdict on those?
Btw, the triode chassis is steel....

[The New Steve H]

We'll see how it works out. If it won't mock up, I'll give my friend the bad news.

Maybe I wasn't so stupid to use 6" aluminum channel in my Bassman clone! I could have mounted a dishwasher on it if I had wanted to.

[ToneMerc]

Metro is selling the Jtm45 chassis and panels again. What is the verdict on those?
Btw, the triode chassis is steel....

I used George's chassis and white back plate for my JTM45, his stuff is correct.

TM

[The New Steve H]

I like the wigs.