Henrik's tube amp builds

AX84 P1

This amp is my take on the P1 amplifier from the AX84 amplifier community (the best place on the web for tube amp geekery, both for beginners and experienced builders). It's a single ended amp with one EL84 and one 12AX7, which all in all puts out 7–8 watts. The amp model is very well documented at AX84.com so you're not going to find any basic theory or how-to guides here on this. The original circuit at AX84 has been revised a few times since I built this back in 2002.
 Being my first build, it's also my sloppiest in terms of component placement, soldering, etc., so I strongly advise you not to copy this if you're doing your first amp. However, it sounds great, it's noise free, and I have used it on many recordings. It has a quite Marshallish sound (partly courtesy of tubes from Mullard and Brimar) and I love to jam with it when my other amps are too loud. Sounds best with a Les Paul style guitar and volume on 10!

My P1 is pretty much ”stock”, except that I used both a rectifier tube (EZ80/EZ81) and solid state rectifying, selectable with a SPST switch. This is a rather useless mod which only affects the B+ voltage, and I always keep it in diode mode. As of February 2015, I have added a 68k resistor across the standby switch as per the Valve Wizard, moved the standby switch from the B+ ground connection to the actual B+, moved the circuit-to-chassis ground wire from the power supply end to the preamp end, and soldered a protection resistor to the speaker jack.
 The components are a mixture of high quality and budget parts. Orange drop capacitors, carbon composition and metal film resistors, Swedish Rifa electrolytics, etc. Probably used more shielded wire than necessary (white cords in the pic below). The teflon wire from Apex Jr is great, especially if you're clumsy with your iron.

The transformers are Hammond 369EX and 125CSE and the chassis was home-bent by a fellow tube amp builder. The turret board was bought at Hoffman Amps and I knocked the turret lugs in place with a homemade ”drill press” consisting of two wood planks, a screw and two nuts. The lugs aren't exactly tightly fit, but the components help keep 'em still.

Again, the soldering could be cleaner and the components could have been spaced out more. In an attempt to put the tubes as close to the front as possible (purely for aestetic reasons) the circuit board got a little squeezed up against the pots. Works fine, though.

The faceplate was drawn in Illustrator by me and engraved by Bits 'n' Pieces Laser Engraving in Washington DC. They make fabulous plates, but alas I've stopped ordering from the because of high shipping costs to Sweden. The words on the faceplate are in Swedish; I just thought that would be more original.

I built the box out of plywood, bought a reissue Gibson amp handle (which seems to have disappeared from the market since then), found a piece of plexi glass (replaced with a thicker one as of 2015) and dressed the thing in dark blue galon (cheaper than tolex but not as durable).

When I get the time, I'm hoping to record some new demonstration videos of all my amps. For the moment, the best way to hear my P1 and Tremolux is in my video game covers at Mutherpluckin' B, which are recorded almost exclusively with those amps.

Back to main page

@lidbjork  lie . b ✇ runtimerecords . net

Parts List

AX84 Community
The Valve Wizard
Paul Ruby's Tech Info
Casey4s' Tolexing Guide
Hoffman Amps (parts store)
Tube Town (German store)
Apex Jr. (cheap surplus parts) BNP Laser Engraving
Hammond transformers
Glasklart (glazier in Sweden)