Jan6418 Guitar Preamp with Distortion

A circuit that i was prototyping about 10 years ago… it will be revised in the next few months… i wouldn’t suggest building it yet, but follow the circuit to give you some ideas about how to wire up the Jan6418 for guitar use.. i plan to put in clipping diodes like in the KLON Centaur pedal.

One of the switches throws the tube into pentode mode for distortion, great clean and distorted tones possible.

I had trouble with Pot orientation, some of them work in reverse, again this kind of got made right before i ceased electronics for a few years and needs to be finished.

I used Mullard Mustard Capacitors as well as Paper in Oil for the tone control.

Power Supply for this can be found here:

Project files available here:

***Original Notes from our Old Website***

I’ve made a guitar preamp based around the Raytheon JAN 6418 Vacuum Tubes, this design has a lot more gain than my previous preamp… it also at the flick of a switch or two throws the tubes into pentode mode for overdrive…. On my guitar plenty of clean tones as well as some crunchy overdrive when you want it…. I tried to get an authentic sound out of it…. one of the ways of achieving this is to use Mullard mustard caps…. In my prototype C1 C3 & C5 are 160v mustards – if you can’t find some (i do have some in my store), Sozo mustard replica’s are propably the way to go, if not paper in oil or Orange Drops will do just as well, just a slightly different tone….

R8 – Input Volume Control
R5 – Gain

R12 – Distortion type in pentode mode
R15 – Overall Volume

R17 – Tone Control

Also 2 Switches, each controlling tube 1 & tube 2 pentode/triode mode – you can use a DPDT switch and wire both with one flick, for more control use two SPDT switches as sound is different in single and dual pentode mode.

Anyway here it is.

Board Layout
Board template for etching
Assembled Board

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