[ezr]

i have the origin amp  st 70   after 10 mins the are some disto in the l.s and now i  cant fix the bais its b 1.5 volts(less)   thank   ezr

[avahifi]

Is the bias going high or going low?  If it is going high, it is likely that you have an output tube failing and pulling too much current. Is one of the output tubes going cherry red? That is a sure indication of failure.  If so, put in a new tube.

If you are not sure what is causing the problem, then swap output tubes one at a time to the opposite channels and set bias again.  See if the problem follows a tube.  If so it is a bad tube.  If the problem does not follow a tube to the other channel, then you have circuit problems.

You can call me about this for more help.  651-330-9871

Frank Van Alstine

[ezr]

thank y frank one of the el 34 its the main prob   
and i will ask y again
if i need to repl the all 4 tubes
ezr