Technical Comments

View the OTL 195 FAQ

The fundamental difference between solid state and tube based technologies: solid state products are current amplifiers with odd order harmonics and tube products are voltage amplifiers with even order harmonics. Well designed tube products will sound much more musical due to even order harmonics and with proper design dispel any myths that exist due to vintage circuit design performance. My tube amplifier circuits all use fast recovery diodes, lots of initial power supply capacitance, low impedance power supplies, no electrolytic capacitors in the signal path, proprietary designed, hand wound output transformers ensuring very musical reproduction with very fast slew rates and low distortion.


All my power amplifiers use a fixed bias system with adjustments on the top chassis. This is a simple, quick user friendly adjustment that is well explained in the operating procedure with each amplifier.

Fixed Bias and Self Automatic biasing Explained;
Cathode/ automatic/ self biasing amplifiers use a large resistor impedance between the cathodes of the output tubes to ground. This raises the cathodes above the ground potential in effect creating the required negative grid number one voltage on the output tubes that determines the current flow and class of operation. Amplifiers with this type of bias do not require any adjustments when output tubes are replaced and are less expensive to the manufacture as no additional negative power supply or controls are required- just a cathode resistor and by-pass capacitor. With cathode biased amplifiers the speed and rise times are much slower due to the large value cathode resistor that is in series with the audio output. Further a large value electrolytic cap in parallel with this cathode resistor has to be used for a shunt AC path ground return and impedance reduction. Electrolytic capacitors in the signal path further degrade the sound quality. Fixed negative bias supplies connect the output tube cathode to ground and have an additional negative voltage power supply. The negative voltage is adjustable and fed to the control grid of the output tube that determines the current flow and class of operation. All of my power amplifier designs use a fixed bias voltage that eliminates the cathode resistor and electrolytic by-pass cap producing an amplifier with fast rise times, superior dynamics and transparency. Bias adjustments are required whenever output tubes are replaced.


McAlister Audio