Lt Boob amp PART 2 - the other boob!

[Greg_L]

I know .... the Ampeg's already built though ........

Well that's no fun!

[Lt. Bob]

well .... you'd prolly end up wanting to recap it

[rayc]

Video as expected...straight forward and clear. Well done.

[Greg_L]

Well I made some nice progress today and I've found a problem already. Not a huge deal, but it'll take some re-figuring. I'll get it in a video tomorrow.

[Tadpui]

Looking good already Greg! That really is a nice kit, all organized and everything.

[Greg_L]

Looking good already Greg! That really is a nice kit, all organized and everything.

Yeah thanks. You mentioned thinking about trying one of these. I'm thinking it could be a good one to start with. But let's see how this one goes first.

[WhiskeyJack]

That is so cool. Very Cool. Good vid too. It looks like Mojo tone put a little more work into the giving you a "kit" then the weber kit did.

So you mentioned some thing about it having a JCM800 preamp in it. Kind of. How much of and what kind of things could a guy do to that kit there to make it into a something like that 20W JCM800 like miners? 18W or even less? or more? I don't know what i am talking about it but i am sure it is likely possible yes?

[Lt. Bob]

as far as power goes 18 watts is basically the same as 20 watts .... virtually no difference in terms of volume

[WhiskeyJack]

as far as power goes 18 watts is basically the same as 20 watts .... virtually no difference in terms of volume

yea no i get that. I was just painting a picture. [mention]JD01[/mention] and i were talking about the 1W JCM the other day and now my gears are spinning. Not that i'd want a 1w. 18 would be more than plenty.

[Greg_L]

That is so cool. Very Cool. Good vid too. It looks like Mojo tone put a little more work into the giving you a "kit" then the weber kit did.

So you mentioned some thing about it having a JCM800 preamp in it. Kind of. How much of and what kind of things could a guy do to that kit there to make it into a something like that 20W JCM800 like miners? 18W or even less? or more? I don't know what i am talking about it but i am sure it is likely possible yes?

Well first off, when I talk about "JCM 800" I'm talking about the 2203/2204. There were other 800s, but in my mind and most others' minds the 2203/2204 are the only ones worth talking about.

It's all in the preamp.

This is the Mojo 18w TMB channel preamp:

18-Watt-TMB-SCH.jpg

This is a 2203 preamp:

Marshall_2203_jmp_preamp.jpg

I know it's probably hard to read that, but trust me, they're very similar. The biasing of the preamp tubes, the cold clipper second stage, the tone stack, besides a few values here and there, they're almost identical. That's the voice of a JCM 800.

With just a few tiny twists the 18W TMB can have an exact 2203 preamp in it. It can be built to exact 2203 specs all the way up to the power tubes. That's where it will get different. 2203/2004s are big bottle amps - EL34s or 6550s. The little EL84s in the Mojo kit won't breathe the same fire that an EL34 can. But still, the voicing will be there because of the preamp is so similar to a real 2203.

You could theoretically turn just about any amp into a 2203. All you need is two available 12AX7s and re-wire it to 2203 specs.

[Lt. Bob]

With just a few tiny twists the 18W TMB can have an exact 2203 preamp in it. It can be built to exact 2203 specs all the way up to the power tubes.

do I want that instead of what Mojo has drawn up?

[Greg_L]

do I want that instead of what Mojo has drawn up?

Nah I don't think so. One thing the TMB is missing compared to the 2203 is the cathode follower stage. That stage is a buffer before the tone stack. Tone stacks can really bog down a signal, similar to a long cable run or effects. So the cathode follower, while not being a gain stage, does act as a buffer to send the signal through the tone stack. I don't know why the cathode follower stage was omitted from the TMB. I suppose they chose to just go without it instead of adding another tube. But let's hear it first. It may not need or want that stage with the amp being relatively low wattage. We would need to add another preamp tube to make it happen, and we'd only use half that tube, so it's probably not really worth it.

[Lt. Bob]

sounds good to me .....

Man, you're really starting to know this stuff sir!

Mojo actually has an amp just reviewed by the guitar mags called the Blackout that is this design only with 6L6's.
The mags love it so I'm pretty excited as to how this is gonna sound ..... I really like EL84s ...... this is gonna be an awesome amp methinks.

[Greg_L]

sounds good to me .....

Man, you're really starting to know this stuff sir!

Mojo actually has an amp just reviewed by the guitar mags called the Blackout that is this design only with 6L6's.
The mags love it so I'm pretty excited as to how this is gonna sound ..... I really like EL84s ...... this is gonna be an awesome amp methinks.

Awesome. Yeah I totally believe that the Mojo folks have done their homework on this design. Not only that, people have been doing this to these amps for decades. It's tried and true so I'm sure it's great just the way it is.

[Greg_L]

Progress update!!!!

[BBvideo=560,315]https://www.youtube.com/watch?v=xOfnaV2 ... e=youtu.be[/BBvideo]

[Tadpui]

Woah that's so weird that they'd forget a turret and design the giant cap so it doesn't fit where it's supposed to go! I'd be furious, mainly because I wouldn't know what to do to get around those problems.

And thanks for the reminder, I forgot to put on MNF

[Greg_L]

Woah that's so weird that they'd forget a turret and design the giant cap so it doesn't fit where it's supposed to go! I'd be furious, mainly because I wouldn't know what to do to get around those problems.

And thanks for the reminder, I forgot to put on MNF

Lol it probably won't be a good game.


It's not unusual to have that cap sticking out the side. Original Marshalls were done that way:


But the mounting of this one was just a little bit off, so it touched the PT. It's actually probably fine, but I don't want those things touching.

[Lt. Bob]

should we fuss at them and make them send a new turret board?

[Greg_L]

should we fuss at them and make them send a new turret board?

That's not a bad idea. If I can find a suitable turret I can fix it. But failing that...yeah a proper board would be good. If you wanna call them and have them send another that'd be great. If I can't find a suitable turret locally then I'm gonna have to rig-job something. Whatever I do will work, but it probably won't be pretty.

[Lt. Bob]

I'll call 'em tomorrow .... if you can find the proper turret it doesn't look like that big a deal but I paid good money for that kit.
So I'll call ...... I can send them a link to the vid and tell them it's at about 2:50.

and it was a pretty good game ..... poor Giants ..... i thought they were gonna do it.