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.
Look into the overlooked. They're usually cheaper, too. Try the 6GK6. It's a beefed up 6BQ5, with different pinout and more filament current, but great for SE or push-pull auto bias.