OR120 chassis

Yay Orange OR120 from back in the day. Caps say 1975. Has trimpots for bias and for hum balance. Just a 12AX7 for V1 driving the tone stack and FAC selector then a 12Ax7 in V2. V2A is DC coupled to a cathodyne phase inverter and then 4xEL34 in the output. Hard to see in the picture but the bias was set so hot (around 90%) that the solder on pin 4 of the two right output tubes is kind of vaporized. The screen grid resistor looks like it’s just sitting in the socket, barely making connection.

OR120 close up

A lot of current flowing in the screen.

OR120 scope

Getting a once over. It was needed for recording but was cutting in and out a lot after being banged around in the car. A heavy-ass V4B fell on it, or something, which caused a power supply capacitor to have a broken lead.  It is the capacitor furthest to the right in the top picture.

Orange OR120 graphic MKII schematic

Orange OR120 Graphic MKII schematic. Cool rotary switch for 6 different voicings.