The Plexi 6V6
meh 1/2002 (last update: 4/2008)
These pages describe an experimental/prototype Marshall/Plexi-style amp which I built using an old Traynor YBA-2 amp (sorry, Traynor fans!). I did this partly for fun, and partly as a test bed so I could fool around with all the various component values used in the many JTM45/1987 amps that have been produced by Marshall over the years.
I also wanted a lower power "November"-style cruncher (see ax84.com) for fooling around in the basement.
This is an ugly duckling - I spent almost no time on aesthetics, and used the holes already in the chassis wherever they were, only drilling new holes where I had to.
Bottom line: It didn't cost much and it sounds great!
Note: YOU CAN GET KILLED by fooling around with the high voltages in a tube amp. Don't even attempt this work unless you have at least some experience and are pretty sure you know what you're doing!
Builder's Note: In many cases, I used whatever parts I had lying around to build this. So, some of the parts are atypical or a bit different. There is no need to slavishly copy every part value and voltage reading. One of these days I'll build a proper 6V6Plexi using commonly available parts. :)
The Schematic is partly original Marshall (most of the preamp), partly November (the PI in particular), and partly my own design.
Starting with the original chassis, I stripped all the parts except the transformers, tube sockets, and the filter cap. Then I made a hole for a third 12AX7, mounted a socket, and connected the filament wires.
I drilled three more holes for the pilot light, mains and standby switches, and mounted the switches, pots, and a NOS Dynaco power supply inductor.
I created a ground buss out of 14 gauge copper wire bent into an Omega shape, and soldered the legs to the chassis (using a big 'ol 120 watt Weller). As shown in this picture, all grounds connect here.