audioguru and RCinFLA, thank you very much for your reply.
The 'transformer is big and operates at a low frequency'. I fed the primary with 50Hz 5-0-5V square wave at 50% duty cycle with 10A maximum current available and the secondary was at...
1. 300V under no load drawing 1A average current at the primary,
2. 275V under Phillips lamp (rated 15W 220V) drawing 2A average current at the primary.
Building an inverter with success, as you see, I need to reverse this phenomenon. What I know is transformers follow reciprocity theorem (constant power at both sides). The DC resistance of primary is 0.01Ohm and secondary is 0.7Ohm (though inductance, and hence AC resistance is unknown).
I had enough of the beginner's fascination with inverters. Now what interests me is a low voltage high current power supply for He-Ne lasers. Interests in resonance, anyone? If not, such a power supply is, still, indispensable.
Please review my former post and advise...