The Most 1980’s JCM800 ever

Dec 4, 2019 | Amplifiers

I always wanted a big Marshall but could never find the one I liked. Then I discovered Ceriatone. They had a hand wired JCM800 dual volume schematic for a hand wired amp. After doing the math and finding some bargain deals the project was a go!

Finding a speaker cab

First part was finding a speaker cab to use. I was trying to find a cheaper but bad condition cab that I could re-condition and save some cash on freight. Trolling Trademe I picked up a 4 x 12 ( or so I thought ). On arrival it was pretty obvious that the cab was NOT a 4 x 12 but actually a 2 x 12. I said to the guy “if it has the half the speakers i’ll give you have the agreed price.” He agreed.

Unbeknown to him, I had noticed a little badge and some strange colours inside. It turned out to be a Marshall 50th anniversary Jubilee cab. Someone had spray painted the silver tolex black, but when I took the back off the cab I could see the silver inside, as well as little badge on the front.

The wood working

I stripped the cab and made a head to match. The whole setup is actually the size of the 2550 Marshall instead of a proper JCM800, so the whole build was going to be a one of a kind. The head had to be double layered around the front and back to give it that Marshall chunk. The whole thing was made from solid pine boards, i’m not a fan of MDF and ply was too big to fit in my car.

Parts collection

With some phone calls and some trading of skills I got some chassis’ made up from Monaghan Sheet Metal. And because I hate getting just one of something, I got 8. I ended up selling the rest and paying essentially nothing for mine ones.

The tolex, transformers and parts came from Triode Electronics, when the shipping to NZ was reasonable. Because I was going for a 1980’s rock / metal thing I went all out and go red tolex, which I never regretted.

Putting it all together

This part took forever as it was only the third amp I had done and it was the first I had done by myself. With lots of calls to dad and lots of googling I got it all wired up. I ended up purchasing some chassis punches to get the tube socket holes ( boy are those handy! ) With a bit of test fitting I was ready to cover it all up. I also snagged some laser cut badges and faceplates through my mates at uni to replace the broken ones on the cab. Also randomly the mesh for the back is cut down gutter guard, the stuff you put in the gutters to stop leaves blocking your gutters.

Firing it up

I was almost ready to fire it up. I ended up going for 6550’s instead of EL34’s as I the samples I heard were more to my liking. I picked up some valves from VintageAudioValves, where I started a great personal friendship with Paul and continue to get valves from.

When I fired it up and I ended up modifying it and adding in external bias tests points with an external bias pot. Still running too hot with the 6550’s I had to change the bias resistor. After a few weeks I also ended up changing to CTS volume pots as the alpha ones went scratchy fast.