NAD - 50w JMP clone

[fitz]

Picked up a homemade hand wired 50w Marshall clone.
Threw out a lowball offer and a quick counter offer later, it was inbound.

Kinda ugly for now, but I have plans...
Here's some listing pics.



Supposedly a Mojotone JCM800 preamp layout, but looks to be TAD caps and various tidbits on a Mojotone turret board.
PT from an old Hammond organ with a Hammond 50w guitar OT, and a Pacific Audio choke



Rear panel is set up with external bias test points and a bias pot between the fuse holders.



I've ordered a proper JMP50w chassis with front & back plates, along with a loop kit from Mojotone.



My current plan is to put the amp in these cabs that currently house my Origin20 #2.

 

[fitz]

Amp arrived today.
Well packaged and nothing looked amiss, so I popped the tubes in and checked the bias.
Played it a bit and it runs fairly quiet unless the gain is cranked.
I'd imagine some neater wiring will do no harm.
Hammond iron sound fine to me.



One of the Mesa El34's is running a little hotter than the other.
Swapped them and the results followed the tubes.



Put in a set of JJ 83's and a pair of JJ 6CA7's.
Much tighter on the bias and sounds more to my liking.



Some quick gut shots.





I'm going to check the schematics and decide if anything needs changed for a '78 JMP 2204 spec.
Chassis and other stuff from Mojotone won't be here for a few days.

 

[C-Grin]

Cool

 

[Robb]

Very interesting project.

 

[BFT Gibson]

Get that bad boy set up to specs you like & it is probably "the" circuit in my experience & SL100 that is rock ! Enjoy maximus !

 

[T-Rex]

Amp arrived today.
Well packaged and nothing looked amiss, so I popped the tubes in and checked the bias.
Played it a bit and it runs fairly quiet unless the gain is cranked.
I'd imagine some neater wiring will do no harm.
Hammond iron sound fine to me.

View attachment 110588

One of the Mesa El34's is running a little hotter than the other.
Swapped them and the results followed the tubes.

View attachment 110589

Put in a set of JJ 83's and a pair of JJ 6CA7's.
Much tighter on the bias and sounds more to my liking.

View attachment 110590

Some quick gut shots.

View attachment 110591

View attachment 110592

I'm going to check the schematics and decide if anything needs changed for a '78 JMP 2204 spec.
Chassis and other stuff from Mojotone won't be here for a few days.

I built a few amps with rescued Hammond iron, Baldwin too. They are fine to use if you get the voltages needed.

 

[Mitch Pearrow SJMP]

Congratulations on a stellar amp @fitz .
HNAD

 

[fitz]

Deceived by ambiguous tracking info - the chassis & face plates showed up today, FedEx.

Front hole placement isn't even close.
Glad I went with the chassis purchase.





Back looks to already be punched for the loop.



2 holes between the fuses and impedance selector.
I'm assuming one would be for a voltage selector?
Not sure about the other, but either could be used for the bias trim pot.
I'll need to add some holes for the probe sockets.



Top will need some work for the lay down PT.
OT holes should work, but I'll need to drill for the 2-point choke mount.
Tubes and caps connections I'm hoping to be drop in.



Too mentally spent from work on a Friday night to start anything.
Circuit comparison to schematics is scheduled for tomorrow after a few mugs of coffee.
Lots of photos before anything comes apart.
Parts list starts with chassis bolts and cage nuts...

 

[DirtySteve]

Looks like fun!