Are KT66's hot tubes?

[BoogieEngineer]

I find those KT66's running way hotter than the EL34's in my other amp. For the EL34 amp, the chassis gets warm after an hour. Whereas the JTM45/100's chassis gets so hot that you don't want to keep your finger there for too long. Not overly hot that you'd pull back your finger immediately though.

I figure it's because the volume on the Plexi is like 8 all the time while the EL34 amp being not a Plexi only needs to run at 3-4 on the volume knob or so. Also KT66's are bigger, they generate more heat I guess. Bias is 35mVDC for EL34's and 36-38mVDC for KT66's. Thoughts?

[SteadyEddie]

I was running KT66's in my plexi and if I ran it impedance mismatched (as I read you are SUPPOSED to do) and it got hot.
Ran the amp at 8 ohms into my 8 ohm cabinet and it ran much cooler. Normal.
If you're running the impedance mismatched because you think you need to, to run those tubes, then that is the problem.

[BoogieEngineer]

I was running KT66's in my plexi and if I ran it impedance mismatched (as I read you are SUPPOSED to do) and it got hot.
Ran the amp at 8 ohms into my 8 ohm cabinet and it ran much cooler. Normal.
If you're running the impedance mismatched because you think you need to, to run those tubes, then that is the problem.

No I don't run impedance mismatch. Just 8 ohm tap into a 8-ohm cabinet. What could be the problem then? I've played with it extensively for long hours without problems, although the heat is bothering me.

[BoogieEngineer]

LOL turned out it was because I opened up the amp to measure bias and experiment with the 100pF bright cap so I had to place the chassis upside down, and the tubes heated up the chassis which was right above them. I turned it around and now the heat dissipates well into the air and it runs as cool as the EL34 amp, if not cooler. My bias resistors are actually 1.2R measured on my multimeter so I'll have to increase the bias a dozen mVDC to actually get a 35mA bias current, so it's great that the amp's running cool now.