TESTED CV4060 S11E12 Power Tube/Valve up to 28W dissipation.

This is a rugged low-impedance valve/tube primarily designed for a series pass valve in power supplies but usable as a power amplifier.

It can operate at anode currents as low as 50 and at 100V has a gm of 10mA/V.
Data sheets available at www.electrojumble.org.uk/DATA_4/CV4060.pdf 

This is electrically similar to the older 12E1