This stuff is made to a price
not a perceived brand name quality so they only add enough to just cover it,, any more and the thermal switch shuts it all down. (kinda clever but still smells cheap

)
A chap asked me to look at a Fender BXR bass head (similar era and heat sink design)
The plastic sticker on the back panel had melted off and was now unreadable.

The Amp kept shutting down even with a fan on it. He admitted he played it loud to keep up with the bands high sound levels.
I added a big chunk of alloy and never heard another complaint.

BTW, the triode is only used as a diode so it really adds nothing to the sonic result. But if it has a valve it will sell more units.
Phil.