I’m starting out on my first valve amplifier build and thought I’d keep a running project log here to share my joys and (inevitable) frustrations.
I started on the idea of building my own amp about a month ago when I realized that it would be easier to sneak a valve amp past the minister of finance as a project than as a purchase.
My initial plan was to start out small and build a simple, single ended 6V6 power amp, which I would initially drive off a Black Star tube pre-amp pedal that I have lying around. If I didn’t enjoy it, I’d leave it at that and my losses would be small. If the bug bit on the other hand I’d have a nice little platform that I could work off and I could then put together a number of little pre-amps and play around a bit. I was even toying with the idea of putting together some kind of power plug on the power amp so that the pre-amps wouldn’t require any transformers. I still think this is a pretty cool idea and may come back to it some time.
Anyway, while trying to source transformers for this build I came across an old Hammond AO-44 on Facebook (a reverb amplifier from a 50s/60s organ), which would give me the transformers and chassis I need… well, one thing led to another and I was upsold to an OA-29, which was the main amp from the organ. It has a beefy power transformer (I believe around 320-0-320V @ 100mA, 5V @ 3A, 6.3V @ 4A), a 20W output transformer used for push pull 6V6s in the original, a sizable chassis and a number or existing tube sockets.
I haven’t received the old amp yet, but I believe that it is still in working order. I’ll probably fire it up and poke around in it before I get started but I don’t think that I’ll ultimately use many of the existing components. So, the question then is… what to build in its place?
A lot of people seem to turn them into plexis but I’m after Fender tones at the moment so was naturally excited when I found this.
It’s basically a Bandmaster pre-amp with a push/pull 6V6 power section and a switchable extra gain stage called the ‘trainwreck’ mod.
I emailed the guy asking for some more information and he directed me to a forum where he covered his whole build.
So right now, I’m looking at using the this schematic and layout as the basis my amp, possibly making with a few mods. There is plenty of extra space in the chassis, so I’ve got a bit of room to play around in the future and possibly do crazy things like adding a reverb tank… hmmm, scope creep much?
Anyway, I think that’s enough of a wall of text for a pictureless first post. I should be picking up the amp on Saturday and will post some photos once I’ve got it in my grubby little hands.
I do have some electronics experience but have never worked with tubes before, so if anyone has any suggestions or comments, I’d be extremely happy to hear them.