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Original Message

The resistors are not critical, except that

Posted by Ralph on January 5, 2016 at 11:01:19:
-as Banat has pointed out, there presence is. The actual values are not.

What is happening is they provide a return path for the bias on the power tubes and also reference the output section to ground potential. Since the actual bias current is very slight, the values of the resistors is not critical. However it is important for them to be able to handle some power, in case the amplifier is given a signal without a load- then these resistors *are* the load and will heat up.

The 600 ohm 3 watt value has proven pretty steadfast over the last 30 years or so.