AX84 November amp

Below is a picture of my “November” amp, derived from the AX84 site (revision 8).

Modifications include:

• Triode/pentode mode switch
• Impedance selector (see below for my wiring diagram)
• 5AR4/GZ34 rectifier, since it was cheaper than the EZ81/6CA4
• “Clean switch” to remove C10 from the circuit at will
• “Bright switch” to reduce C4’s value
• Bias adjustable from top of case (see pot at back of top between EL84 and 5AR4, green tip jacks on either side of the EL84’s).

It's in a 2-space 10″ deep rack enclosure from SESCOM. From left to right, we have:

• Jacks for channel 1
• Jacks for channel 2
• Volume 1
• Volume 2
• Bright switch
• Clean switch
• Treble, mid, bass controls
• Bias select
• Presence control
• Pentode/Triode mode
• Ultralinear/Pentode mode
• Standby
• Power

Inside view. Output jacks and impedance selector are at bottom of picture, perf board for power supply at right, perf board for PI at left, rest of wiring is point-to-point.

Detail of bases of V1 and V2. Found nice turret terminals with ceramic insulator that screw right into enclosure. There's a couple of them at the bottom of this picture. If I had known about these earlier, probably would have dispensed with the terminal strips.

Diagram of impedance selector switch wiring, as seen from back. Used a 690-C6P0304N-A from Mouser, set to 3P3T.