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I couldn't adjust properly the bias of my ST70. I have tried 2 sets of EL34s but the bias is still too high, more than 2V for the Groove Tubes and 6V for the XF2 against the standard 1.56V. Can anyone tell me the probable cause of the problem?
Follow Ups:
The "lytics" is not replaced. I also suspect there's something wrong with the selenium because I can't adjust the bias of both channels. I'll replace the selenium to see if it works. Thanks for the advice.
ANY decades old electronics requires some basic maintenance prior to use. Read the Asylum FAQ, under Tubes section, Vacuum Tube Primer article. Notice that there is a more-specialized Dynaco Doctor forum listed on the Asylums' Home page under Sponsor Forums. Good luck.
Perhaps the Selenium rectifier in the bias supply is on its last legs. Since Selenium rectifiers are ticking TOXIC time bombs, replacement, as a matter of routine, is in order, in any event. A UF4007 Silicon diode gets the job done. A resistor may be needed in addition to the UF4007, as the forward drop in Silicon is smaller than the forward drop in Selenium.BTW, have the PSU 'lytics in the amp been replaced? The 'lytics literally dry out over time.
Eli D.
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