bassybeats | Bassybeats Projects

Building a Mini Marshall Plexi

by bassybeats | Dec 4, 2019 | Amplifiers

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.

$D:\GuitarAmplifierPCBs\Production\Plexi SE PCB\Schematics\Plexi SE PCB (Cascade) - Schematic v11.dwg$

$D:\GuitarAmplifierPCBs\Production\Plexi SE PCB\Chassis Layouts\Plexi SE PCB (Cascade) - VJ Chassis Layout v4.dwg$

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 2×10” 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

The 1950’s style Fender Champ

by bassybeats | Dec 4, 2019 | Amplifiers

Technically the second amplifier I built, the 5F2A Fender Champ build was created out of left over parts. I had a bunch of leftover wood, tolex and fibreboard from the 18 Watt 1974X build ( and the green from dad’s build).

The build

Unfortunately I didn’t take many in progress pictures, but the idea was to build a 1950’s radio two tone combo, half black and half green. Pretty much all the tolex and grill clothe was left from the Marshall style builds. I managed to get some faux Fender badges laser cut at uni and spray them silver.

The tolex is wrapped in the old Fender style, with the sides getting done first and the top and bottom being over lapped by about 20mm. Then I just hit the inside with some black paint.

Almost all the parts were left from other builds other than an output transformer. Again not too many gut shots during the build. Its all standard turret board hand wired like the days of old.

As well as the the badge I laser cut of the faceplate and just rubbed in some white paint to make the lettering standout.

I ended up ditching the V-shaped back panels, as cool as they looked the tolex just kept peeling up even using Ados contact adhesive.

The final product

I have since sold this amp to someone else that might like it more than I do. It did sound awesome but I prefer something a bit more easily over driven like my 5 watt Plexi.