I like music and playing guitar, but I also like to tinker with things that make music. I lately thought I should understand how vacuum tubes work. I first learned the basics of electrons flowing in tubes--diodes through pentodes. I bought a few old 78 record players from the 40s and 50s with tube amps to repair, mostly just replacing old capacitors with modern, safe equivalents. In every case, the old tubes themselves worked just fine.
I then thought I should make a practice guitar amp for my little music room where not much volume is needed. There’s lots of info on the internet, and I thought Robrobinette.com was particularly good. He recommends starting with a Fender Champ build, because it sounds good and is a relatively simple amp with just a preamp tube and one power tube.
I approached this build with the desire to use as much stuff as I had lying around. I rewound some 12-volt AC transformers to be an isolation power transformer and an output transformer. I used a silicon bridge rectifier instead of a tube rectifier. I had a 12AX7 twin triode tube available. I bought the requisite resistors, capacitors, tube sockets, pots and DC filament transformer. I bought a 12AL6 pentode that seemed like it would work well with the lower voltage from my isolation transformer. I also bought an old Fender Frontman 15 for its cabinet and 8” speaker.
The build was pretty straightforward but I spent a long time chasing down some loud hums. The solution ultimately was shielding the transformers and grounding the filament negative supply line to the chassis.
In the end, the amp sounds great, though more distortion than surf would probably like. Especially with some boost ahead of it, it gets plenty loud.
A Champ-style amp is a great first build for any of you thinking about such a project.
(Awaiting a pot for treble.)
If I'd stop buying old guitars to fix, I might actually learn to play.
Bringing instruments back to life since 2013.
Last edited: Nov 14, 2021 18:37:13