Audio and Electrical Engineering
1993-2021 Studio Guitar Amp Build
In 1993, I built this guitar amp with Hammond Organ transformers. It originally was purple felt, which has since rotted and been replaced with green, and sadly, I don't have any original photographs of it. Still after all these years, in early pandemic, playing it full tilt, part of the power supply failed and fried a great deal of the circuit and burned out many parts. So, it was time for a re-build.
The original amp was setup for a pair of EL-34s and would do 20 watts give or take. The limiting factor was and still is the output transformer from the Hammond Organ. The original speaker was a 1980s Carvin High Energy HE-12. I believe this speaker was made for them by Eminence in KY.
The Re-Build
First up was to strip the chassis of all parts. I sanded all of the aluminum bare to remove dirt, corrosion, rosen and glue from the previous build. I repainted the transformers, this time in black and started planning the layout for the new can capacitors.
The biggest challenge was I was young when I originally built this amplifier and the layout was less than ideal. Still, I stuck to the original layout and tab point-to-point construction.
The beauty of this amp has always been its flexibility. It has switchable tube and solid state rectifiers in the power supply, and they very much so do sound different, no matter what you have read on the Internet. It also has output tube switching. This amp can use 6K6, 6V6, 6L6, EL-34 or 6550 output tubes. Shown here is a set of Chinese KT-88s.
The original version had 3 tubes in the pre-amp, but I dialed that back a bit in the final build to just 2. The amp is using 2 American 12AT7s for the pre and phase splitter duty.
I settled on a pair of 1950s brown base RCA 6K6GT black plates that were NOS in the box. This is a very overlooked tube from the American heyday of tube manufacturing. Of course, the outputs can be switched at anytime for a different sound.
I did replace the Carvin speaker with a Celestion Blue — a 15 watt made in the U.K. Alnico magnet speaker.
Back together and ready to rock.
