The first vacuum radio tube was made around 1900 in laboratory and became commercial mass production in 1920. In mid 1920’s tube radio became popular and lot of manufacturers such as RCA victor, ATWATER KENT, KOLSTER, MARCONI etc. made famous radio models. At that moment, stand alone tube amplifier was not popular. In early 1950’s,…
It was well known that a triode voltage amplifier is easy to build even for beginners. Please see the picture. This is a 6SN7 tube voltage amplifier: The only thing we have to determine is RL, RK, RG and B+ supply voltage. DIYers could easily suggest that RL= 30 Kohm, RK=1.2 Kohm, RG= 470Kohm and a B+…
From mid 80’s I went back to tube amplifiers and tried to build a 30W 6L6 push-pull mono block pair with 6SN7 drive tube. I selected a popular circuit diagram see picture: Stage 1 voltage amplifier calculation, plate output. Grid input load of next stage neglectable. Stage 2 phase spliter calculation, plate and cathode output. Grid…
Self bias comes from voltage drop of a cathode resistor, in case of minor gas inside glass envelope, the slightly plate current increasing will lead to negative bias increasing so that this is a self protection to prevent over current. See picture below, an example of cathode resistor bias(348 ohm, -34V). Fixed bias comes from…