• 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.

preamplifier

If you're looking for OTL headphone amplifiers, you might want to take a look at some of the ideas at http://www.tubecad.com. Broskie has at least four or five schematics--probably more--for OTL headphone amps. Various tubes are used, depending on the circuit, including one with paralleled 6922/6DJ8s for the output. It would give you an interesting basis for comparison.

Grey
 
Preamp?

Just put a 1 meg pot on your input before it gets to the driver tube on your amp if you are just looking for volume control. Unless you are needing a phono section. A CD player or tuner have high enough outputs that a volume control potentiometer is all that is needed to control the amplifier. It doesn't look like you are wanting to change the bass and treble.