Dr. Gregory L. Charvat

Quad Tube Amplifier

Quad Channel Vacuum Tube Amplifier

  • 14 tubes total
  • 4 class AB (‘ish) tube audio amplifiers in one chassis
  • EL34 output tubes
  • Approx. 80 watts RMS output power per channel
  • 20 Hz to 25 KHz -3 dB closed-loop bandwidth
  • 0.45% THD
  • Single power supply for all 4 amplifiers


This is the quad tube audio amplifier portion of my tube home theater system. In designing this amplifier I have attempted to squeeze as much power as I can out of a pair of EL34 pentodes while still maintaining high fidelity performance resulting in a bandwidth of 20 Hz to 25 KHz and a THD of 0.45 % while achieving a peak output power of approximately 80 watts RMS per channel.

Photos of the Quad Tube Amplifier

Photos of the quad tube amplifier, its installation, with the covers off and under test.
General power amplifier block diagram
Quad power amplifier schematic
Quad power amplifier power supply
Transient response before of old fall ’05 amplifier design before latest loop compensation
Open-loop Bode plot before compensation
Open-loop Bode plot after compensation networks
All power amplifiers are capable of 20 Hz to 25 KHz -3 dB closed-loop bandwidth. Closed-loop Bode plot after compensation