Not too sure if the further dilution of the Amp Garage with handfuls of sub fora is a good thing...
WARNING: not very neat and tidy
Just thought I would post a few pics of my JCM800 build and talk you through a little of what went on.
I had a Marshall build in mind back in 2012 when I saw Mark Fowler's Stage 50 based on the 2204.
It seemed a great addition to my #102 and AB763, especially as I wanted to run the Dumble and Marshall as a dual amp rig.
Martin Manning then suggested the Classictone 40-18095 PT modelled on a Drake I believe which was being developed at that stage and features 3 secondary taps of 560v, 625v and 690v as well as a 5v rectifier tap.
Well I was pretty busy on my 102 build leading up to Christmas but I built the 2204 combo cab over the holidays from a good dry 21mm pine floorboard and made the baffle from 18mm MDF. Covered it in British Racing Green tolex and Marshall salt n' pepper grille cloth. A new G12-65 Heritage was installed, coutesy of the same lovely ladies in Suffolk who made my original one back in the 80s!
The chassis 18.5 x 6.5 x2.5 came from Modulus Amps in Scotland as did the block logo nameplate.
I finished the 102 in January and got straight on with the 2204. I ordered the PT from Triode as soon as it was available. Very good comms also from MC, by the way. OT used was an MC 18025 and the 5H 120mA choke. The set arrived from Triode exceptionally well packed!
I got on and started planning the layout and drilled board which I got from Modulus as I am lazy....! I used a combination of Metro and Ceriatone layouts with the JCM800 schematic.
A PPIMV is a must for me so that was fitted too.
I had a few NOS resistors left from my 102 order so these went into the mix.
Filtering was via F&T, 2 x 50+50uF cans and one 32+32uf dual on the board.
I added an octal socket for a GZ34 tube rectifier and wired up the 5v but have left it for now as it sounds fine as it is. I don't think there is much to be gained from running a tube as the capacitance needs to be reduced to 50 from 100uF when the tube is being used.
I tried all 3 HV taps but the 625v gave the best balance of headroom and driveability as you might expect....
Plates are 435vDC biased at 35mA.
Grounding is a star ground near the PT, I put in the solder tags for a Larry scheme if it was noisy -it isn't.-
Mods to the circuit are:
PPIMV in place of the 220K bias resistors.
It works very well and is essential IMO.
.047 bass cap in place of the .022.
Mid pot 50k instead of 25k.
Single input so no treble peaking circuit.
Bias test points.
Yesterday I got crazy with the board mounted bias trimmer and dropped in a pot at the back in the tube/diode switch hole. Much better!
