A guy by the name Thomas Weissbach on diyaudio.com has built a monster amp from Russian GU-46 (ГУ-46) pentode. Thread here
The valves can make up to 700W with a 2.5kV anode voltage. In this build though they are 150W per channel. There is almost 80kg of custom iron in there!
The valves can make up to 700W with a 2.5kV anode voltage. In this build though they are 150W per channel. There is almost 80kg of custom iron in there!