The Aviatrix is a single-ended amp built from the remains of a Ward’s Airline console radio and a Vox Valvetronix combo cabinet.  6V6 output, approx 5W.  The speaker is a Weber Alnico Signature 10S.  The variable voltage regulator (VVR, a.k.a. power scaling) mosfet and ridiculous overkill heatsink were scavenged from a Sun e450 server power supply module.  The Airline console provided the transformers and the chassis.  I’m currently using the Airline-branded 6V6.

This project started as a quick and dirty junkbox build after I finished another, more complicated project, the Neutron Star, for a friend. I wanted to quickly throw together a small amp that I could keep at work–there’s a spare room where I can practice at lunchtime, etc. The Neutron Star had turned out well, and I wanted to do another build where I was driving a pentode followed by a bootstrapped cathode follower. I started with the Airline chassis, which in addition to the power tube and rectifier, had holes for a 9-pin tube and a 7-pin tube. To keep things relatively straightforward, I decided on a 12AX7 for the input stage and CF, and went hunting for a 7-pin pentode.

After some googling for schematics I saw that one or two people had used the 5654 in guitar amps. Also they were cheap. I bought a lot of 18 on eBay. When they arrived and most of them were marked “FAA” I figured that for a sign, given that they were going into what was once an “Airline”.

This was my second experience building (mostly) point-to-point on terminal strips, and I really started to enjoy it. I definitely pushed the limits of what would fit in such a small chassis. I also did a lot of improvising. For example, the 12AY7 was added after the original build was complete. I had an amp that sounded really nice, but I couldn’t resist going for more gain, so I made another hole in the chassis and crammed in a few more term strips. It was a fun way to work, more flexible than coming up with a board layout before building. I did a lot of unsoldering/resoldering. At this point I only have one resistor substitution box, so I was forever tacking in parts. I really need to get at least a cap sub box.

Cab-wise, I’m about halfway there. I covered the cab with olive drab fabric from an army surplus half tent shelter I picked up at Berkeley Surplus for $10. I gave that a couple coats of shellac, as you might with a tweed cab.  I used Zinsser Bullseye clear.  I removed the chrome from the grille with a wire wheel on a drill, then rusted it for a few days by repeatedly spraying it with salt water.  When it was good and rusty I removed a bunch of the orange oxide with steel wool and treated it with some Van’s instant gun blue.  Repeated that a few times, then coated it with Hoppe’s Gun Grease.

Clip!  Fairly random noodling, but what the hell?  Starts out very dirty, gradually cleans up, then back to max grit at the end.  Please pardon the mic-bumping noises–garage was cramped/messy and I was twiddling knobs while playing.

current schematic

[soundcloud width=”600″] https://soundcloud.com/john-hannon-1/aviatrix[/soundcloud]

FAA 5654 tube

FAA! This tube approved for all your avionics needs..