My AX84 Mods


I originally used a EZ81 rectifier but I replaced it with a pair of 1N4007s. It made the amp run cooler and increased the B+ by about 10V. In this amp I don't hear any real difference between the SS and tube rectifiers. Had I known that I would end up a SS rectifier I could have saved myself some effort. With the SS rectifier there is one less hole to drill, one less obsolete tube to track down, one less glowing tube to burn yourself with and about a $7 savings in parts. Of course if I hadn't built in the tube rectifier in the first place I would forever wonder if I was missing something.

Inspired by the AX84 Chameleon I added an octal socket so I could replace the EL84 with a 6L6. It was an interesting experiment but tone-wise it was not very interesting.

The 6L6 needs to be driven harder than the EL84 to get it to distort. When I cranked up the amp with the 6L6 installed I found it harsh sounding. I suspect most of the distortion was in the preamp.

I then added a switch to bypass the tone stack in order to drive the 6L6 harder. The amp was now a Champ-style circuit except it used a 6L6, the plate voltage was only 250V and some of component values were different. I put a master volume in front of the 6L6. This gave me precise control over the amount of power tube distortion. I still couldn't get it to sound as nice as the original AX84 circuit with the EL84. To my ears the AX84 with the EL84 is richer sounding and has a bell-like quality.

I would have liked to try some more tweaks but I was running out of room for more switches and pots and I didn't want to tear up the original AX84 circuit. This experience convinced me to build a Tweed Princeton clone for my next amp.

Page updated 3/2/00.