by Shannon Parks » Wed Nov 20, 2013 5:54 am
The limitation is the voltage swing you get from the 6SL7 and the ratings of the transformer. Unfortunately when one increases the cathode bias in an otherwise static circuit, the cathode voltage will go down, meaning there's less headroom for the voltage swing. So you can only get more watts by increasing the B+ voltage, too.
But if the transformer can handle the heaters, then yes, you can just drop them in.
Shannon