[Amps] Alternative cooling strategies for SB-220?

[Rob Atkinson]

Not sure what mode you want to operate (i.e. what duty cycle) but if
high d/c the duct trick with the blower remoted may have this problem:
 the 220 fan is normally placed in the cabinet in such a way that air
is drawn in through the p.s. from what I remember of it.  If you run
duct direct to the rear hole next to the RF deck, you loose that p.s.
cooling through the v.doubler and B+ transformer.  But I have no idea
how hot the p.s. gets under normal condx or if it gets hot at all.

Another thing you can try is a tx keyed relay switch on the power line
to the fan that bypasses a resistor on tx but is n.o. so the fan power
goes through a voltage dropping resistor to slow it down so it is only
full speed and noisy when you are transmitting.   You have to wire it
so the fan is not powered in series with one side of the B+ primary
(if that is the stock SB220 arrangement).   If you make a long RTTY or
SSTV tx and the tubes get real hot you will need to use a timer relay
with a set delay time so the fan speed drops around 30 seconds after
you switch to rx.

Just some ideas.

73

Rob
K5UJ