These seem to be a trend lately. This is the second one I found to turn into a project, this one is a Columbia (Sony) C-690tr. It's a small portable unit with 1 12ax7 and one 12BH7, pushing a 4x6 speaker. Here's the schematic: I only had to move one wire to be able to plug a guitar into the inputs and play through it. It has tons of gain, a pretty decent amount of volume, but a bit of a muffled tone without much treble. It is usable as is but it really seems like it would benefit from some tweaking to make it more guitar friendly... Here is a modified schematic with some proposed changes in red: I've changed the input and a few cap and resistor values as well as adding a tone control and a grid stopper to the power tube. Thoughts and suggestions would be much appreciated!