I have 2 dynacos, VT70 tubes4hifi kt77 gl and a vintage st70.
The problem if it is, is in my vintage one. Running the bias on 1.35 everything is ok, but biasing 1.57 the bias begin to go up slowly. Half an hour more or less, the bias go to 1,70 ore more and the tubes (SVETLANA WINGED C) are so red and there is a terrible noise that invite you inmediatly to disconect the amplifier. Is there a typical problem?. I dont mind to go at 1.35 but i am afraid that in the future will have the same problem.
Thank you, please to meet you all and Sorry for my horrible English, I am Bask in the north of Spain.