This amp is currently under construction. I just added the Fostex FT66H Supertweeter for the last octave. Also it draws the sound a bit from the Altec/Oris horns, so they seem to beam a lot less at the high frequencies. It is hard to hear this amplifier, but the sound gets a lot better positioning, the sweet spot is much larger and also the sound is more fine, loose, more sparkling. This is a very good addition to the system.

The amplifier consists of a 6CS7 double triode with pre and power triode part. It is build like a very simple singled-ended amplifier, the pre-triode drives the power triode, which is connected to a 10k:8 amorpheous single-ended output transformer specially optimized for the frequency range of 1kHz to 100kHz (less inductance than normal). The amp is capable of delivering 0.7 watts, more than enough for this frequency range on the 100 dB sensitive Fostex FT66H supertweeter.

Sound is incredible good! It is now build on a piece of wood. More (pictures, schematics, etc) to come right after I have build it definitive (somewhere this year).