May 31, 2007

Vox Stuffing, or Flip this Vox?

I've wanted to flip an amp ever since seeing what people were doing with the Epiphone Valve Jr. So I set my sights on doing something unique with a SS Vox Pathfinder.  I figured the 8" speaker and 16"x14.5"x8" cab would be perfect for a small amp such as the Firefly from

So, I picked up a working Pathfinder on eBay for $42.00, promptly gutted it and began work on a layout plan for a Firefly. Looks like it will all fit in the original chassis. Then one night while taking a break from the layout work, I decided to plug my November Project head ('s 18 watt Plexi) into the Vox speaker. I was impressed! I got a good crunchy sound and when I backed off the Strat volume, I had a nice chimey sound too. All at bedroom volume! I immediately scratched the Firefly plans and proceeded to figure out how to stuff a November chassis in this cab.

It wasn't long before I realized I would have to use a separate chassis for the preamp and power amp. I just used the original chassis to house the preamp. Had lot's of room especially since I would get B+ and filament voltages from the power amp. The power amp chassis layout was a bit of a challenge, not because it was too small, but because the iron and tube layout had to also fit around the speaker in that small box. After working out the major layout of the power amp, I proceeded to layout the boards.

With board layout and assembly done, it was just a matter of final assembly. I used the same assembly techniques and grounding scheme that I've used on my other amps. The preamp umbilical cord used separate STP cables for the B+ and filament, and teflon insulated coax for the signal. The cord was hard wired to the preamp and connected to the power amp via an octal plug and socket. There were no surprises during construction or startup. I even got the feedback polarity correct the first time!


Download the schematic and full size board layout. (vox.pdf, filesize =  395k)

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