I am a long time lurker, but I've learned so much from this community, a lot of which went into this build, that it feels good post my build report here.
This is my first amp build in 30 or so years, and it was a long build process, around 8 months from start to finish. A good chunk of that time was just being too tired from overwork to work on hobbies but I did spend quite a bit of time problem solving how to fit everything I wanted to into the build. I started with buying the Hilbish chassis but decided early on I would not use the PCB. My main concerns were protecting the transformers because I intend to ride it hard, and put it away wet. But also a couple of useful, but defeatable mods. Some high points:
I added internal pre-rectifier fuses on the B+ in addition to the mains and post rectifier B+ fuses. UF5408s for the rectifier.
MOVs on the mains to protect the PT from power surges.
MOVs on the OT primary to protect it from spikes.
Failsafe load for the OT.
Quad bias supply so each power tube can be biased on it's own.
Separate elevated heater supply for the preamp tubes.
All non-transformer wiring is Tefzel or Teflon.
TOCOS pots and heavy duty Carlin switches.
Isolated input and output jacks, one ground connection to the chassis, one true ground.
Defeatable arc-protection and grid-stopper for the cathodyne PI.
A switch to lift the EQ. I also had a switch for some mods to NFB, the EQ lift turned out to be much more in character of the amp (garage-stoner-doom) and one of the mods needed to go.
Slave output gone.
Effect loop send gone.
Effect loop return remains but is relocated to the lower input position on the left. The stock effect loop circuit is crap, but the effect return is useful to bypass the preamp to use an external preamp.
I changed it so the 220K resistor on the grid of the input is only active on the lower two throws of the gain switch. I may remove it altogether.
I have 100 feet or so of shielded Teflon wire and figured I'd need to use it in a number of places but really the only wire I had to shield was the NFB wire. The amp is very quiet (when it should be).
The Hilbish chassis is stunning. 14 gauge steel. High quality powder coating. Roll cage is awesome.
The Mercury Magnetic transformer set is great (but pricey AF).
First electricity was a pucker moment for me but it went smooth. I started with the variac around 30V no tubes to sanity check with voltage measurements, and then moved to a lightbulb limiter with tubes. Bias was easy.
Here's the guts. Starting with the power section that is under the main board.
It's done aside from the shell and some additional labeling on the chassis. I may make the Merlin cathodyne changes always on, I have a few ideas for mods for the switch I'd have open. I won't be building the shell until later this year when all the amp projects I have going are finished and I'll build shells for all of them at once.
Next up are some tube preamps, starting with VH4 (channels 2,3, and 4), and Wizard MTL (full preamp). Thinking SLO and Mesa Boogie Mark I for the next two. Next amp is a Sunn Model T clone, I have the Mercury Magnetics transformers in hand, and a custom chassis is being built.
Matamp GT120 build
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JustinHarvey
- Posts: 3
- Joined: Fri Oct 25, 2024 4:02 pm
8 others liked this
Matamp GT120 build
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Raoul Duke
- Posts: 759
- Joined: Sun Apr 17, 2022 1:00 am
- Location: S.E. Mass.
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Re: Matamp GT120 build
That’s awesome. Not everyday do you see a Matamp clone. They are really cool amps for sure with a unique tone.