At last i am nearly there.
The above driver circuit worked but i could only get about 2V pk-pk across my heater.
Here's a summary of what i am doing.
Mains supply feeds a 6V transformer, this goes through a vol control to adjust amplitude, this then goes through a 0-360 Degree phase shifter, this then feeds a 15 Watt(upgraded from 10Watt) Class A amp which feeds one secondary winding of a 9V large toroidal transformer, the other 9V secondary winding is connected across the heater of the 5U4G.
Tonight i finally got to the point of powering up, and the 15Watt Class A easily gives me my heater amplitude and a lot more if needed, it glows
I still have a couple of issues that should be no problem, i am using a 0-6 0-6 transformer, 1 winding provides my mains frequency and phased 50Hz reference, i used the other 0-6 winding to rectify and supply my phase adjust board, it looks like i am getting some distortion because of this, so i now need to move the phase shifter to a new supply and just use the 0-6 transformer for my reference.
I also have a 450-0-450 transformer hooked up via a variac - not had the bottle to fire this up yet.
Something strange happens also, with the variac turned to minimun which is giving me about 3-4 volts ac on the anodes, i connected 1 scope probe to my driver circuitry and then connected the second channel across the heater which is isolated from the driver circuit and suddenly i got lots of hash if the scope gnd is connected to only one side of the heater, i find this strange everything is isolated and connecting the scope ground to the heater should not matter anyway, so the ground probe is shorting gnd from the driver side to the heater side of the valve, surely it should not matter if 1 side of the heater is grounded?
Not got my good camera here but took a snap on the notebook.
I have also attached a shot of the sine across my heater, you can see some distortion on the top of the waveform.
Also i have uploaded the 2 pdf's which show how to build the Class A, i had to modify the design, it was originally a 1969 design, this pdf gives value changes to drive a 3Ohm load, so i added this mod to the 2000 version, i used 2 TIP3055 with 0.1 Ohm emitter resistors in place of each 2N3055 and a BD139-16 in place of the 2N1711