Stacey Campbell
AX84 P1
AX84 P1 top view
Top view.
AX84 P1 front view
Front view.
AX84 P1 internals
Here's some views of a guitar tube amplifier I constructed back in the late 90's using schematics from The Cooperative Tube Guitar Amp Project. This project is called the AX84 P1. I built Rev 10 with the optional solid-state rectifier. (Note: the schematic has been revised several times since 1999 and the most recent schematic should be used for new builds.)

I used a Hammond 10x6x2 chassis which turned out to be a bit of a squeeze, but everything ended up going in okay. The four huge caps got stacked into the back corner. The vacuum tubes are made by Sovtek, a Russian manufacturer, and the two transformers are made by Hammond in Canada. The output transformer was built only a few days before it turned up at my house.

Total cost of the project (keeping in mind I borrowed the tools and soldering iron) was;

            269EX power transformer        35.06
            125E output transformer        33.11
            12AX7WA tube                    9.90
            EL84 tube                       8.40
            Hammond 10x6x2 chassis         11.00
            2 x 9 pin sockets               3.76
            mono input jack                 3.50
            8" 50W/4Ohm Eminence speaker   44.10
            SPDT toggle switch              3.65
            DPDT toggle                     5.07
            SPST toggle                     3.29
            various pots                    5.00
            500v 40uF caps                  5.07
            fuse holder and fuse            2.86
            AC cable and grommet            9.50
            misc resistors, caps, diodes   23.84
            wire, solder terminals         15.00
            total                      US$222.11
Minimum order quantities on most resistors and caps pushed the price up, the most annoying case being C14 (0.005uF/1500V) where Digi-Key had a minimum quantity of 10 at $1.26 a piece (note: C14 has been removed in later P1 revisions). Plus the speaker could have been had for about $10 less at a number of places I found a week after my order went in.

Anyway, it sounds great. Very nice tone, and very little noise that only becomes evident at high volumes, and is quickly swamped once the guitar gets played.

Oh yes, and I discovered later that since the invention of the transistor most "first projects" generally aren't high voltage. Live and learn.

Update: 2024

The amp still sounds great after almost 25 years of admittedly light use. I will probably check the electrolytic capacitors soon and see if it needs to be re-capped.