What the bias measures BEFORE you remove the tubes doesn't matter. The correct bias adjustment for the ST-70 is 1.56 Volts. Be certain that's what you end up with, after all the other steps mentioned by Viridian are followed. Also: The bias needs to stabilize for 15 minutes to 1/2 hour(let the amp warm up) before testing/adjusting the bias(every time). One more thing: Each channel will fluctuate according to adjustments made to the other. Don't just set one, then the other and forget it. Check/adjust back and forth, until they both read 1.56 Volts. Happy listening!
2 Quad EL34 sets for Dynaco ST-70
I am new to tube amp and I really need your help. I have one current quad Russian EL84 running in ST70. My friend gave me another brand new quad Mullard EL34 Russian tubes for me to test sound. What is the best way to remove old quad tubes out and replace new quad tubes? If I do not like new one, I also can put my old tubes back.