"N_Cook" wrote in message
...
Just repaired a tube amp , problem unrelated to this.
But it seemed odd to me to have valves , in inverted
orientation , ie under a pcb with SM resistors on it.

Anyone foresee temperature cycling problems/ dislodged SMD in the future
with such arrangements.

As they say "If it can be done, some fool will do it". Given that heat
rises, I see no benefit whatsoever to putting a tube which converts 70% of
the electricity fed through it to heat underneath a PCB. All it's going to
do is shorten the life of the PCB components and, quite possibly, the tube.
There's a reason why most tube amps have the tubes exposed or covered only
by a mesh grille...

just my 2 cents.