• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

RH84 build & quite a few questions...

After years of searching I came to the same conclusion as Gary Pimm, there is only one ideal candidate for a Schade driver and that is the 6AU6 or one of its relatives. Cheap as chips compared to the weedy audiophile pentode drivers and robust in use.
Boy, it really depends on what you're after. I have used the 6AU6 successfully in two such designs, but they don't always fit the bill.