6BQ5/EL84's can get hot enough to burn your fingers & still survive for years.
Actually,the hottest operating receiving tube I ever ran into was the 6
AQ5 (a miniaturised electrical equivalent to a 6V6).
Trying to pull one of these out of an (operating) tube type car radio under the dash,is quite startling!
Burnt fingers & dented head!
Some of the amp circuits you have shown us,wouldn't have been considered good design back in the day,as it was usually better to run two big output tubes,rather than EL84s in parallel push-pull.
Obviously,even when they were designed,the supply of audio power tubes was starting to dry up,hence the use of multiple (more available ) devices.
I remember many years ago,a friend of mine referred to fixing a homebrew guitar amp which used 807 's in the output.
In those days,there were still a lot of tubes which had the grid brought out on the top cap.
A trick often used in troubleshooting was to touch the top caps,injecting a bit of hum in so doing.
When it stopped causing a "blurt" at the speaker,you had found the faulty stage.
807s bring the plate out of the top cap,& the"homebrewer" had neglected to use the proper insulated connector.
My friend used the above technique,& received an unwelcome surprise!
![Grin ;D](https://www.eevblog.com/forum/Smileys/default/xgrin.gif.pagespeed.ic.QVVz6XIT20.png)
All of which brings me to ponder why Guitar amp manufacturers didn't use,not 807s,because they were already too old,but 6146s & the like,which have serious power capabilities,& were still readily available.
Perhaps a lack of information about using them in audio circuits?