Building a Mini Marshall Plexi

Inspired by the sound of my JCM800 I longed for a more portable version with the same snarl and drive. It was then that I discovered Terry Stinger’s Plexi SE, a 5 watt version of the 6L6 based Marshall classic.

Doing it the hard way

Like all my projects I wasn’t doing it the recommended way. This build is based around converting and Epiphone Valve Jr. to a Marshall. The board should / would have dropped in place. I wanted a custom route. As well as not being able to find an EVJ I wanted to build a combo.

I found that Musical Power Supplies did transformers in the specs I needed. The PT275.2i and the OT10SE, which I only ended up using the power transformer as dad found an old fender champ output transformer. Monaghan Sheetmetals for the win again. I ordered a pair of 18g alloy chassis based off the dimensions off the Blackstar HT-5TH.

Wiring it all up

Populating the board was relatively straight forward, finding some of the caps in the right voltages was tricky but luckily Ryan at The Amp Shop had some repair parts in stock. Matching up the Epiphone transformer wiring to that of the MPS transformer was harder than expected, the virtual grounds were different and dad and I ended up actually cooking the transformer on the first power up and filling the whole garage with smoke!

Speakers and cab

eBay came to the rescue again as I was trying to source speakers. I ended up modelling the physical dimensions of the amp off my Blackstar HT-5TH 2x10” combo. It was the perfect size and volume with a 2 x 10” open back cab. I settled on a pair of Celestion Ten 30’s / G10R-30’s.

Mum and dad recently did a re-fit of the kitchen, so I ended up gathering up all the awesome Rimu ( New Zealand native timber ). The cab needed a bit of sanding and filler to tidy it up ready to be tolexed. The front baffle was 12mm plywood, I built it using the same method as doing an 18 watt Marshall baffle, in 3 bits.

The Amp Shop also supplied the tolex, piping and grill cloth, this time a nice cream colour paired with the JTM45 style grill cloth and black piping. I have essentially modelled the whole thing of the look and size of the Blackstar at this point.

After a little bit of playing it was very evident that this thing could sound amazing, I say could as it has a huge amount of hum that got louder with the volume knob.

Off to Clarry it went. Once I got it back I was informed that I shorted the 6V6 cathode to ground, but was also told it was very hard to find so I didn’t feel so bad. Some lead dressing and ground jacks and this thing was as quiet as a mouse now. And boy does it sound killer cranked with a Epiphone Casino running through it!

Left to do:

  • Glue on badge
  • Laser cut faceplate

Materials:

  • MPS PT275.2i power transformer
  • Champ output transformer
  • Rimu boards
  • Plywood baffle
  • Celestion G10R-30 x 2
  • Marshall style knobs and pilot light
  • Plexi SE board
  • Mojotone tolex, piping and grill cloth
  • 18g folded alloy chassis