Block-JAN6418

A simple yet flexible gain stage based on the JAN6418 subminiature pentode.

Features

• Filament supply options:
  • 2x resistor voltage drop
  • Optional bypass capacitor
• Pentode/Triode mode:
  • Triode: Jumper (0 Ohm resistor) S2 to the plate
  • Pentode: Solder a resistor between S2 and B+, and S2 and ground
  • Pentode: Solder leads to an off-board potentiometer in lieu of the two resistors
• Impedance controlled PCB stack-up:
  • Top, Inner-2, and Bottom copper fill ground planes
  • Signal lines on Inner-1 layer
  • Power lines on Bottom Layer
  • Vias along signal path for improved impedance control
• Mounting holes on either side of the tube for securing using rubber or silicone grommets, and a pair of 2.54mm (0.1in) zipties.

Background

I've been designing a blues harp preamp for a buddy of mine, and it occurred to me that all valve gain blocks are essentially the same, just with some variance in component values. Because I tend to have different ideas for an individual gain block, and different ideas about interstage connections (capacitor types, tone stack, delay/echo, etc), having this board allows me to play with different ideas more easily than pulling up components from the breadboard, but at the cost of components soldered into place.