Vostok - 1.5 KW HF linear amplifier using GU-81M ( GU81 GU81M ГУ81 ГУ-81М ГУ81М) tube - by YO6PMX

10 years ago, Serghei Pasko, EX8A published on CQHAM.RU a series of articles describing the performances of the "old", "hopeless" "lazy" tubes GU-81M, GK-71 and GU-13. There were alot of ham operators who criticized him, but there were a few who confirmed his results. When I readed for the first time his articles, I felt that he was right, it was some sort of "resonance" with what I was thinking about these tubes. I took me a few years until i felt myself ready to build Serghei's amplifier with gu-81M, but now here it is, as strong as predicted... EX8A WAS RIGHT!
The linear is driven in the first grid, the anodic voltage is 3KV under load and 3.4 KV in idle mode. The idle current is 80 mA. The original articles can be found here : www.cqham.ru/Hi... , www.cqham.ru/pa... and the results of EX8A are confirmed also by RA6ED here: www.cqham.ru/ra... and here: www.cqham.ru/pa...
The second grid regulator described in the original article of Serghei was not working for me, but I found a very good regulator offered by UR3IQO, which works very well. The schematic can be found here : skydan.in.ua/PA...
73 de YO6PMX !