V404 is the record head driver.
V408 is part of the bias oscillator.
Assuming you are using the unit as a microphone preamplifier, those tubes are not needed.
Take note of the rise in heater voltage, correct if necessary.
Neither is V402 required, whose voltage gain is essentially lost in the record calibrate voltage divider
(100k into 10k). V402 is there for a reason but is not necessary for preamp usage only.
