Michael A. Terrell said:
RCA used 16 parallel 6146 as the video amplifier to modulate a 4CX250
in their TTU-25 series TV transmitters.
It's sometimes more economical to use multiple small devices, rather
than have to find some single big device to do the job.
With semiconductors, it can often be advantageous to use several cheap
transistors and run them gently, rather than push a big expensive one to
its limits. If there is a lot of dissipation, the thermal paths from
multiple chips to the heatsink are parallelled, which allows a smaller
heatsink that can safely be run hotter.
In the case of valves, there was often a big jump in price between a
'consumer' output pentode and the next size up, which fell into the
'industrial' class. For guitar amplifiers, which were, in essence,
'consumer' equipment, it made sense to stick to consumer valves, even if
it meant using more of them.
It also made the power supplies cheaper because bigger valves usually
needed higher voltages, which meant special rectifiers and paper
smoothing capacitors. A smoothing system with paper capacitors worked
out more economical if the capacitors could be relatively small and the
extra smoothing was provided by chokes. The chokes made the equipment
bigger and heavier- and the higher voltages made it very dangerous for
semi-skilled 'roadies' to service (and more spectacular when it went
wrong).
