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Check the votage on the grid side of the caps. You may have to disconnect the caps to the outputs to get an accurate reading. Its obvious that you don't have enough negative voltage so increase it in the negative direction. The voltage on the schematic is just there for someone doing a cursory inspection of the amp to see if everything is in range and assumes you have enough adjustment range to achieve proper bias for your particular set of tubes. You are working from a 400 volt AC source. If you can't get -70v from that, you better send it out. Usually the resistor closest to the output of the bias source is changed. You may end up having to change all of them if the change needed is extreme. You have the amp so you have to determine this. You should be able to test without the standby engaged, so you can spare the power tubes any more pain. You need to have it on, of course, to do the final bias set.
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