New build: 2204 Mojotone kit

[GuitarBilly]

@Bill - any chance you have any gut shots of your Ceriatone 2204 you could share?

I don't, I opened mine the other day but didn't take pictures, the amps are at the lockout so I can't get to them right now... but there are some pictures online:





As for grounding, what MojoTone is recommending is the way it always has been done by Marshall etc.. don't overthink it

[itchyfingers]

As for grounding, what MojoTone is recommending is the way the have always been done by Marshall etc.. don't overthink it

Are you not aware this is Steve Overthinkinit Grimespace?

[GuitarBilly]

As for grounding, what MojoTone is recommending is the way the have always been done by Marshall etc.. don't overthink it

Are you not aware this is Steve Overthinkinit Grimespace?

Yes, I am very aware

[Tortuga]

Who dat?

[Tortuga]

It begins...

[GuitarBilly]

It begins...

Very cool of you to build this along with your kid. That's going to be a great experience for him

[Tortuga]

Thanks, Bill

Got some of it started today...



Transformers, Filter caps, power/standby switches, and input jack. Spent rest of time figuring out minute details, like which side of the chassis do the tube sockets sit, and which hardware size goes with what.



Added another minor project - a smoke absorber that we made for making things a bit safer while soldering on big projects like this. We made if from a PC fan, carbon filter, a wall-wart, and will be adding some tape to temporarily hold it together. Dylan's going to 3D print a case for this





Then (for the Lego nerds ) - we finished this one, which was started last year (Father's Day & birthday gift) and worked on a bit at a time when the boys were over...

[Zozobra]

It's not a wildly high gain amp and your grounding scheme is limited by the layout and the use of can caps. I wouldn't worry about it. Build it to the docs and worry about it afterwards if you're convinced that ground noise is a problem.

[Marc G]

I know nothing about building amps BUT..... I would suggest building it to Mojotone's specs first... get it working...then fuck with it IF there's a problem you think needs addressing.... this would make troubleshooting MUCH easier if you do encounter any issues when you fire up the amp for the first time

[Zozobra]

This is the definitive article on grounding best practices. You'll see that very few commercial amps do this

http://www.valvewizard.co.uk/Grounding.pdf

[Tortuga]

Y'all make good points. I was really thinking I'd try out the floating ground idea, but I guess I'll build up a baseline by going with the Mojotone wiring diagram. Kinda overwhelming having to work entirely from that one sheet, though.

[Marc G]

Y'all make good points. I was really thinking I'd try out the floating ground idea, but I guess I'll build up a baseline by going with the Mojotone wiring diagram. Kinda overwhelming having to work entirely from that one sheet, though.

the kit didn't come with a step by step build manual? just the layout?

[Tortuga]

Nope - just a schematic and wiring layout. It's considered a more "advanced" kit, so you're pretty much on your own. Lots of builders use the build manuals from other, similar designs as a general guide. I've looked at the ones from Metropoulos (Plexi) and Mojotone's 18-watt, and they've been helpful. Plus, there's a LOT out there on the various forums, etc.

This is what comes with the Brit800 kit:

[Tortuga]

...of course, when you go to other marshall-related forums, you wind up coming across this fucking guy



holey mega fucking mega signature, batman

[PatF]

You could pull the ground buss off the pots and wire it like the mojotone layout. Use non conductive standoffs except for the last one. Notice Mojotone grounds to the chassis at the input end which is correct by theory and proboably quieter. The Triode grounds at the PSU side which makes more common sense. I hate cooking the pots by soldering that buss to the back of them. Yes, it is proven to work million times but it still sucks.

I've done the Larry style grounding a few times and its cool too. I have the Metro kit step by step pdf if you can't find it.

[Tortuga]

You could pull the ground buss off the pots and wire it like the mojotone layout. Use non conductive standoffs except for the last one. Notice Mojotone grounds to the chassis at the input end which is correct by theory and proboably quieter. The Triode grounds at the PSU side which makes more common sense. I hate cooking the pots by soldering that buss to the back of them. Yes, it is proven to work million times but it still sucks.

I've done the Larry style grounding a few times and its cool too. I have the Metro kit step by step pdf if you can't find it.

Heya!!!

Yes, please - anything you can share would be MOST welcome!!!

[IAmTheKurgan]

I used this video to get an idea. Granted, its an EL84 18w kit, but it was still super helpful. I used it more for the order of building the subsystems and how to plan out the build.

https://www.youtube.com/watch?v=ym49IRaL0Ho

[Tortuga]

I used this video to get an idea. Granted, its an EL84 18w kit, but it was still super helpful. I used it more for the order of building the subsystems and how to plan out the build.

https://www.youtube.com/watch?v=ym49IRaL0Ho

Thanks Steve!

Checking it out today

[Tortuga]

Been busy... got a bunch of stuff started (and restarted) over the past week and especially today.

All the topside hardware (transformers, caps, etc.), with the exception of the bias control is all in place. First two cap cans are grounded, heaters done, OT and choke transformer wiring is prepped and just about ready to go.

Doesn't look like a lot, but it's coming out well. Did some pre-work on the turret board, too. That'll be coming up soon.

[Tortuga]

My son 3D printed this smoke absorber for me

[IAmTheKurgan]

Coming along nicely, Steve!!

[Tortuga]

Here's some build updates, including a few pictures focusing on some mods I've been incorporating into the amp kit.

Didn't like the standard power transformer wire layout and made a few changes. The chassis had 4 extra holes (shown in green below), so I decided to use them.



So I pulled the bells off and revised the wire placement (moved a few wires to the other side):



<...and while it remains to be seen if doing so will introduce noise in the power circuits, I'm pretty confident these changes should be fairly safe>

Then I got everything placed in the pan - should be able to see the 4 holes for the power transformer being used (4 left-most grommets)



Another thing of note in that last photo is the black grommets installed on V1 (lower-right component in that picture). I had read some things about V1 being susceptible to microphonics and quite a few builders adding some 1/4" grommets between the socket and chassis to help as shock absorbers. Sounded like a plan...

[Tortuga]

Some test fitting of the board



Decided I wanted to route hookup wires as they were done on the actual Marshalls using a through-hole in front of the solder pads, as you can see in this pic



The circuit board provided would allow me to connect the hookup wiring to the terminal posts (with the wire laid on the top of the board) or underneath. I didn't like either of those options, and since there was plenty of room on the edges of the board, I went ahead and drilled them out, which you may or may not have noticed in an earlier posting above:



Then, started installing test points for bias current, plate voltage, and ground. Decided to put the safer test points on the back panel along with the common ground, and the high voltage plates are hooked up on the top of the chassis, which requires removal of the back panel for access. Thought that was a pretty good compromise, and worked well with the wiring.



First bias test point installed - holes for other bias and ground points have been drilled in this pic (they run horizontal)



And here you can see the orange test points on top of the chassis for getting the plate voltage of each power tube



And here was my first pass at hooking it all up, using some stand-in 5% 1-ohm resistors that I knew I'd be replacing soon with to-be-ordered 1% precision resistors

[Tortuga]

Walked into a FUCKING DISASTER of screw organization boxes that let go from the shelf I'd thrown together a few months back... spent an hour or better today cleaning it all up.



Then I decided I wanted to redo the whole bias test point hookup today, and then would install the new precision resistors when they arrive (hopefully) tomorrow. This one turned out great, and all I gotta do is hook the 1-ohm resistor between the bias test point and the ground lug.



And then this one FUCKING BROKE on pin 1 (8:00 position in this picture)... too late to get an order in and get something shipped for the weekend, so will try the two last remaining electronics stores in my area tomorrow to see if either of them have any octal sockets.

[Tortuga]

So I decided to use the rest of the evening putting together the main circuit board. Got a little more than half way done. Not perfect, but I think it's turning out pretty damn good so far. And yeah, I researched some more on grounding, and decided that floating the ground using a rail was a good way to go (plus I think it looks cool, not to mention makes it a little more challenging). Worst case, if it's noisy, it's not going to be hard to change out the grounding scheme from what I'm putting together right now.