Manfred,
At first sight (at those 6AQ5 characteristic curves) it seems possible to increase the primary AC and obtain lower anode voltages during conduction. Another way would be to keep the original primary AC but to lower the DC center tap supply voltage. Both ways seem so easy to realize that Tek would have tried this and likely had reasons to reject it.
I can think of some attention points but have no answers.
The inevitable higher (average) screen current and voltage might require a more powerful feedback tube.
The grid 1 currents seem to increase only at the very low anode voltages, so might be no problem. BTW grid 1 operates at considerable positive voltage during part of the oscillator cycle. Most curve are for zero or negative grid 1 voltage.
The grid 1 primary feedback winding number of turns, and RC-network to grid 1, might need revision in order to have the desirable conduction time of the 6AQ5. Probably also to avoid "motor boating".
Albert
