I didn't have a vacuum tube power amplifier for a long time and I had been wanting to build one for quite some time. I came across a suitable schematic on the DIY Audio forum. The original schematic was by Tubecad.com and many people had built the amplifier with great success, so I decided to give it a go as well. Along the way a forum member "artosalo", a fellow Finn, took the time to optimize the schematic even further. I tried both, and artosalo's version measured better with more power and less distortion, so I chose his schematic over the original one. The amplifier has several operation modes which are selectable by toggle switches. The amplifier can be used in either triode or ultra linear mode, with or without global negative feedback (GNFB). All these modes have a slightly different sound characteristic, all of which sound fantastic.
The amplifier uses vintage Russian military 6N1P tubes as preamp and phase inverter tubes and a matched quad of JJ branded EL84 (or 6BQ5 in the American RETMA designation system) as the power tubes in a push-pull configuration. The output transformers are made by the Polish company Toroidy, the exact model is TTG-EL84PP.
The enclosure is made of pine, aluminium and as a decorative feature I made sleeves for the power supply capacitors out of some copper pipe I found at my local scrapyard. All the metal parts of the enclosure are made of recycled materials. It is safe to say that this will be the last amplifier enclosure I will make out of pine. Yes it is very cheap and easy to work with, but it is an absolute nightmare to make it look good. I went through at least two dozen experiments to come up with what I have now and it's still not perfect.