Hi all. Every time I power up my ST70, I have to adjust the bias because when it is measured the bias often is above 1.56, like around 1.6. Adjusted to around 1.56 (it cannot be maintained at 1.56 flat), then after a while it drops to around 1.52 or sometimes 1.48. Is it normal that bias of tube amps has to be adjusted everytime when powered up? Or is there a problem with my ST70? I have replaced the quad capacitor, the selenium rectifier with diode, the complete driver board and its components, all resistors (except the two 15.6ohm) and capacitors; and am using a new set of Chinese Shugang EL34. Thank in advance for any help.
Also, any one knows where I can find pictures that show the values of all components on the two boards of PAS-2, like those that I've seen in this forum for ST70?