Huh, thanks - but frankly, I`d be more happy with "normal" forum talk about DIY, exchange of ideas and experiences - then some "teacher role"...
Source impedance in PS to the first capacitor - this is our Rt (secondary resistance + primary resistance "transformed" to the secondary side); plus impedance of vacuum tube recifier in series. It isn`t linear resistor, but for our purposes (with known current draw and voltage "drop" through the tube) we can simplified it with series resistor of typical value, say 100-300 Ohms (depends of the diode).
About tube/OPT loading I wrote many times, for example:http://audioroundtable.com/GroupBuild/messages/1111.html
http://audioroundtable.com/GroupBuild/messages/1113.html
http://audioroundtable.com/Tubes/messages/665.html