There is a quiet extractor fan above those amps, ventilating to the outside.
However, these Quad amps use Peter Walkers current dumping design. The 909 amps power transistors are biased class B and run very cool, but there is a small very good class A amp which feeds an error correction signal to the output devices. So the performance is actually class A and does not have the normal low signal level crossover distortion of the usual class A/B amps at low signal levels.
The Quad 405 and 405-2 amps power transistors are actually biased class C! You would not think the circuits would be stable, but they are. They are superb amps.
These amps do not make the huge amounts of heat that class A amps do. They also run significantly cooler then the ubiquitous class A/B amps. The other ice feature is that the part count is very low compared to other amps.
Quad 909.
Quad 405 II
Pure design elegance.
