Studio HAVOC

Detailed Circuit Description

The signal enters the first 12AY7 triode, center-biased and fully bypassed for maximum gain across the audio frequency spectrum. The VOLUME control then attenuates the signal according to the user’s preference.

The second 12AY7 triode is configured as a cathode-biased cathodyne phase inverter.  The signal enters the cathodyne through a large grid stopper to prevent frequency doubling.  The cathodyne is slightly unbalanced, due to the bias resistor in the cathode circuit; this slight imbalance adds a touch of even harmonic distortion to the power stage for extra character.  The cathodyne sends an inverted signal out of it’s anode and a non-inverted signal out of it’s cathode.

From there the signals pass through large power valve grid stoppers (to avoid gain-spike distortion), and on to the two EL84 power tube grids.  The power tubes are cathode-biased push-pull Class AB and provide 10 watts of output power.  The push-pull configuration results in excellent power supply ripple noise rejection, while cathode biasing allows for easy power tube replacement.

The filaments of all three 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.