Wiring Valves In Parallel For Low Noise
One theory about how this works is as follows – that electrons do not land
on an anode in a constant, steady stream, but instead in 'clumps'; each 'clump'
produces a current pulse that is converted by the anode resistor to a voltage 'click',
and a succession of such 'clicks' constitutes noise. The theory says that two valves
in parallel are extremely unlikely to produce identical 'clicks' in the same polarity
at any same instant, so that the noise of one 'subtracts' from or 'cancels out'
that of the other, the net result being less noise than would be produced by a single
valve alone.
I think it's simpler than that. By paralleling two valves, you effectively create
one, but which has double the anode surface area. This greatly increases
the number of electron 'clumps' arriving at any instant, along with a greater likelihood
of a comparable number of 'gaps' (absences of 'clumps' – please try to keep
up), with a correspondingly increased 'noise cancellation' effect occurring in the
anode itself (although it's really two anodes – yes I know it's confusing).
There is an analogy in magnetic recording tape – each individual magnetic particle
is like a tiny bar magnet, which generates a 'click' when it passes the gap of the
playback head. Again, a rapid succession of these is what produces 'tape hiss'.
The simplest and most effective answer is to increase the width of the tape. Then,
many more particles pass the gap (of increased height equal to the increased width
of the tape track), thus increasing the chances of 'clicks' in opposing phases,
or cancellation.
You can go have a quiet lie down now...