Re: Which KT66?
I like KT66's biased hot in most cases too. This is the case with most 6L6 types as matter of personal taste I guess. The same is not necessarilly true of EL34's. In my JTM45 I run KT66's hot.
The typical max plate dissapation of real British KT66's was 27 watts. This is quite different from typical regular 6L6 types. Many early 6L6's and 5881's actually have max dissapation ratings of 18 or 20 watts. Many are 25 watts, and some 70's 6L6 models such the 7581's and some 6L6GC's, are 30 watts. You really need to know what exact 6L6 your dealing with when biasing.
As for the heater current draw, most regular 6L6's only draw about 0.9 amps. The real KT66's draw 1.3 amps. EL34's draw 1.4 amps and KT88/6550's draw 1.6 amps. If the amp normally operates EL34's or 6550's okay, it should handle KT66's okay too. But an amp designed with regular 6L6 tubes in mind may not be able to handle them.