Sink or Swim MY First Amp Build JMP 2204

[lesexypaul82]

Yes this is indeed my first amp build. In fact i didn't even own a "tube" amp until February this year.
I like to jump into the deep end and learn.. But please dont fear for my safety. I have experience in manufactoring and assembly of electrical components, testing of and reworking of..
This will not be a rush job.

I welcome any and all suggestions! I do intend to build this the way Mojo Tone have supplied the "schematics and diagram" for... Once i double check paper to digital then to proper well known version.
Then once it makes a noise Unless its pure heavenly let the mods begin.

I ordered from Mojo Tone a British Style 50w Amplifier Kit based on the JMP 2204. Now there are two version buildable in this kit, 1976-1978 and 1978- Rebrandingcto JCM 800
I had decided to build the 1978 Version... That may change,

Ordered 25/4/2023 (sorry i mean 4/25/23 hehehehe) delivered 3/5/23 a whole week ahead of predicted delivery.. I choose the Fed X option.. Did i mention shipping to Australia?
Everything looks great! Some pieces dont have the quaility feel to them but they are also things that dont really need to be.

1st Issue of the build discovered.. Lets see who spots it.

 

[Gunner64]

What's with the faceplate dude?.. the mojo 50w mv jmp kit should be a 2 holer, with master volume and preamp volume. Not volume 1 and volume 2.

 

[Gunner64]

I built the same kit. Sounds fantastic. 78 specs with a few tweaks.. check out my thread on it below in the similar threads column.

Mine was all correct except they sent a 500k pot for the presence control. The sent the correct pot out immediately after I brought it to their attention.

 

[lesexypaul82]

What's with the faceplate dude?.. the mojo 50w mv jmp kit should be a 2 holer, with master volume and preamp volume. Not volume 1 and volume 2.

Congrats picked it straight away.
Resolved it straight away for me to! Poor old sales guy was even getting confused with all the different builds called 50watt British style.

 

[TheKman76]

Someone's fallen down the valve amp rabbit hole, eh?
Melbourne?

I watch with great interest.

 

[BlueX]

Interesting, I will follow your project. Layout to reduce hum might be something new compared to your current experience.

In case you do not already know. Robrobinette's web pages are great resources
- How to build: https://robrobinette.com/How_To_Build_a_Tube_Amp.htm
- Start-up procedure: https://robrobinette.com/Tube_Amp_Startup.htm

 

[lesexypaul82]

Interesting, I will follow your project. Layout to reduce hum might be something new compared to your current experience.

In case you do not already know. Robrobinette's web pages are great resources
- How to build: https://robrobinette.com/How_To_Build_a_Tube_Amp.htm
- Start-up procedure: https://robrobinette.com/Tube_Amp_Startup.htm

Thanks for the tip looks like some great reading to be had.

Someone's fallen down the valve amp rabbit hole, eh?
Melbourne?

I watch with great interest.

Fallen?? The enlightened path more like it!
Close enough to Melbourne that its still considered a trip to the big city! Far enough away that the music shops don't even stock tubes...

 

[Gunner64]

Yes this is indeed my first amp build. In fact i didn't even own a "tube" amp until February this year.
I like to jump into the deep end and learn.. But please dont fear for my safety. I have experience in manufactoring and assembly of electrical components, testing of and reworking of..
This will not be a rush job.

I welcome any and all suggestions! I do intend to build this the way Mojo Tone have supplied the "schematics and diagram" for... Once i double check paper to digital then to proper well known version.
Then once it makes a noise Unless its pure heavenly let the mods begin.

I ordered from Mojo Tone a British Style 50w Amplifier Kit based on the JMP 2204. Now there are two version buildable in this kit, 1976-1978 and 1978- Rebrandingcto JCM 800
I had decided to build the 1978 Version... That may change,

Ordered 25/4/2023 (sorry i mean 4/25/23 hehehehe) delivered 3/5/23 a whole week ahead of predicted delivery.. I choose the Fed X option.. Did i mention shipping to Australia?View attachment 129683View attachment 129684View attachment 129685View attachment 129687View attachment 129688View attachment 129689
Everything looks great! Some pieces dont have the quaility feel to them but they are also things that dont really need to be.

1st Issue of the build discovered.. Lets see who spots it.

The one thing I changed from the mojo layout was tapping the bias supply before the standby switch as opposed to after the switch as its drawn on the mojo schematic. Some 2204 Marshalls wrongly have it wired like that and mojo just copied it.

The idea is to have negative voltage to the control grid before b+ is applied. A couple members here pointed out that mistake on the layout to those of us building mojo kits.

 

[syscokid]

The one thing I changed from the mojo layout was tapping the bias supply before the standby switch as opposed to after the switch as its drawn on the mojo schematic. Some 2204 Marshalls wrongly have it wired like that and mojo just copied it.

^^^ This! ^^^

1st Issue of the build discovered.. Lets see who spots it.

I see another issue too. Mojotone supplied the kit with silver mica caps instead of beefy ceramics!!!

 

[Central Scrutinizer]

Looking forward to watching your build progress.

Glad Mojotone is taking care of the faceplate so quickly for you. They are a good company to deal with.

 

[syscokid]

Some Windows Paint magic:



Added the extra red wire from Standby switch to the 160K bias feed resistor

 

[lesexypaul82]

Some Windows Paint magic:
View attachment 129747


Added the extra red wire from Standby switch to the 160K bias feed resistor
View attachment 129748

Thank you. This was the only thing i was considering to do differently.
So lift the 160k away from yellow standby wires. Run that new Red wire to it and make a new place to solder it down..

 

[lesexypaul82]

I see another issue too. Mojotone supplied the kit with silver mica caps instead of beefy ceramics!!!

There is two 5watt ceramics...

 

[syscokid]

There is two 5watt ceramics...

I forgot about those 5W ceramic screen resistors. But what I meant was the small value caps, like the 1000pF, 2x 500pFs, 47pF, and the 10pF. But in reality, I'm just screwing with ya and you could always change it later if you decide to.

 

[lesexypaul82]

So you can all play along at home here are the Schematics and Wiring diagram ill be following.

 

[BlueX]

Some Windows Paint magic:
View attachment 129747


Added the extra red wire from Standby switch to the 160K bias feed resistor
View attachment 129748

I asked a question in the Workbench section, on the indicator lamp. Made a separate thread not to high jack this one.

 

[lesexypaul82]

Now i feel like i can start..
Banged together this holder for chassis.
ill refine it and update later on after the first amp is done..
I find it strange that Mojo dont have a step by step instruction book. So im going to follow Metro's build steps. (as in order to do steps)

 

[Axeplyr]

Following... the same kit just showed up at my door.

 

[Pete Farrington]

The one thing I changed from the mojo layout was tapping the bias supply before the standby switch as opposed to after the switch as its drawn on the mojo schematic

Phew that’s good. It’s just from the photos in your build thread, I can’t see how it’s any different to the stock Mojo?
The Mojo board needs a turret adding to mount the 160k dropper.

Incoming! HNAKD, Mojotone MV JMP 2204

www.marshallforum.com

 

[Gunner64]

Phew that’s good. It’s just from the photos in your build thread, I can’t see how it’s any different to the stock Mojo?
The Mojo board needs a turret adding to mount the 160k dropper.

Incoming! HNAKD, Mojotone MV JMP 2204

www.marshallforum.com

I changed it after the initial photos were taken, which was when you guys brought it to my attention. I didn't add a turret however, I just soldered to the resistor like the grid stopper resistors are soldered at the power tubes. The wire goes through a hole in the board, so it's just not hanging there in space.