One Tube 6L6 Transmitter experiments 1

I built my one tuber during 2005. This was my first attempt ever to build tube gear and I must say that I really find it fascinating and fun to experiment with. The circuit was taken from a modified version of the Stancor 25-B Hammanual circa 1939. The circuit was modified by W0VLZ and can be found on his very nice website at the following url http://www.prismnet.com/~nielw/6l6/6L6.htm The attached pic shows my version. I was never able to get the output power up to a decent level, expecting to be able to generate a stable signal at about 7 watts output about 13 watts input (300v plate voltage and about 45mA plate current). I spent some time trying different link turns but never was successful. Today I disconnected my tank circuit and instead connected in a tank circuit from an old Knight T-50 transmitter. This was a success from the point of view of being able to generate about 6.5 watts into a 50 ohm dummy load. However the frequency is extremely unstable. I note that the screen voltage varies significantly although I also suspect that the cheap meter I am using is picking up stray RF which is affecting the readings. I will now try a different meter and report the results. I also notice that the crystal itself is getting warm. What could be causing this? Much heat is also generated off the voltage divider which in itself consumes about 5 watts of power. However I am not convinced that it is this heat that is heating up the crstal. Do I have the wrong screen voltage? I will try to adjust the screen voltage in order to see if I can get a better operating point for the xal.