Baby Jim MkII

A small valve guitar amplifier. The original Baby Jim paired a JCM800-style preamp with a 5 W single-ended, class A EL84 output stage. The MkII keeps that output stage and builds out the front end: more gain, more features, and far more flexibility and switching.

The circuit. ECC83 triodes make up the preamp; a single EL84 drives a single-ended output transformer from a 380 V centre-tapped power transformer. The controls are Gain and Master, a three-band Bass, Middle and Treble stack with a mid shift, and Presence, with Deep and Bright voicing switches and a Boost for more gain. There's an effects loop, with send and return.