The project starterd after a long search for schematics on the Internet. I didn't find anything worthwile, so I decided to experiment with the so-called ideal concept. It contains three principles: first - minimum number of parts in the signal path, second - minimum number of output tubes, and third - usage of newest parts for tried and true solutions.

This is how it looks with KT88 and E88CC tubes from JJ electronics

Inside Dark shot

Specifications:

Max Power Output With Nonlinear Distortion >1%, Using KT88 Tubes: 40w (E34L Tubes - 30w)

Nonlinear Distortion With Power Output At -1w , - 1kHz Freq.: 0,05 %

Nonlinear Distortion With Power Output At 10w , - 1kHz Freq.: 0,4 %

Global Feedback is only 6 db. If we leave out the feedback loop, distortion will increase twice, but it's still not much. It's more a matter of taste really.

Input Level While Input Impedance Is 100 kOhm.: 0,5V

Output Impedance: 4 Or 8 Ohm

Power Supply: 250w

Class A Power Amplifier (one channel uses 65w at idle, KT88 vacuum tubes)

This ampifier projects combines modern techniologies and time tested tube equipment. The circuit of the amplifier is symetrical from input to output . The audio signal enters an input selector through a gold-plated connector using a thick audio cable whitch is not longer than a few centimeters. Volume control circuit uses an Japanese ALPS high quality potentiometer. First apmlifier stage has a E88CC JJ tube. It works as a phase inverter. Driver stage uses a second E88CC JJ. The signal enters a push-pull stage (KT88 JJ or E34L JJ tubes) through a pair of paper-in-oil capacitors. Output transformer is connecter in an ultralinear circuit. To prevent hum ant ensure stability, a star ground method is used. Tube heating is grounded via a 100 Ohm potentiometer. The power supply is a special toroidal transformer, whitch is produced as an audio model. Anode power supply circuit has an RC filter, made from 1500uF capacitors. Here are the integrated amplifier and power suply schematics. Some measurements made with SpectraLAB software with power output of 1W, 10W and maximum (THD >1%).

Replacing output tubes with EL34s, the amplifier changes it's character - the sound becomes softer and more natural.