Mild HAVOC

Detailed Circuit Description

The signal enters the first 12AX7 triode, center-biased and partially bypassed for maximum mid to high frequency gain, and is boosted well above the noise floor. The GAIN control then attenuates the signal according to the user’s preference.

At this point the signal enters the second 12AX7 triode, warm biased to add even order harmonics and timbre, and leaves to the third 12AX7 triode stage setup as a DC-coupled cathode follower.

A large grid stopper on the DC coupled cathode follower encourages squashing the signal for ultra tubey compression.  The cathode follower sends the signal to a traditional Fender style tone stack with BASS, MIDDLE, and TREBLE controls, and a LEVEL control bolted on to the end.  The LEVEL knob controls the signal level that reaches the fourth 12AX7 triode, the output stage.

The output stage is configured as an AC-coupled cathode follower, but with a large anode load to restrict headroom to safe line levels; this prevents large signals from escaping the preamplifier and damaging line level devices, but maintains the cathode follower’s low (as far as tube devices are concerned) output impedance.  The tone is crafted before this stage, so don’t crank the LEVEL for tone’s sake (use the GAIN for that); cranking the LEVEL beyond what is needed will only add noise and possibly unpleasant clipping.

The filaments of both tubes are powered by a 6.3 VAC supply, fitted with a humdinger trimpot with grounded center tap.  This trimpot is adjusted at the factory to remove nearly all heater noise. DO NOT OPEN THE CHASSIS OR ATTEMPT TO ADJUST THIS TRIMPOT YOURSELF; DANGEROUS HIGH VOLTAGES ARE PRESENT VERY NEAR THE TRIMPOT.