In college, I was interested in building high power audio amps. (I have
since outgrown such foolishness). Anyway, big power transistors were
EXPENSIVE, like $30 in the late 1960s... a LOT of money.
To avoid frying them, I fused the circuit w/ 3AG fuses. That worked fine,
but every so often a fuse would blow w/o explaination. I chased this for
days w/o success. Eventually, I was testing the thing from a low freqency
sine generator at a Hz or two and I noticed the fuse wire was alternately
heating (and bowing) then cooling (and straightning), and deduced they
were failing by metal fatigue.
The same thing could be happnng here. When the unit is turned on, the fuse
may briefly heat and then cool... eventuall leading to a fatigue failure
at some random time, for no apparent cause.
FWIW,
-John
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Eventually both fuses of the IF section had blown as a matter of
surge protection. My house is right next to a transformer site from
the electrical regulator (20.000V transformed downto 220V) and our
power supply in the house is quite unstable.
Since I often disconnect and reconnect the power I suspect a surge
took place after reconnecting the power blowing out both fuses. I'll
go out and see if I can find a good surge protector or whip
something up myself.
Since you're very close to the transformer substation, you probably
have the best (lowest impedance / highest voltage / best stability)
power available on that circuit. People downstream from you only have
it worse. Or, in other words, I fail to see how being close to the
transformer makes the power supply in your house "unstable" -- on the
contrary, your "predicament" is usually desirable!
I'd argue that you don't really know what caused the fuses to blow. I
suspect that unless you completely clear the reference circuit as
pointed out by Chris Trask/Al Jamison in their posts, that's still
suspect. It must be a common failure mode. I don't know what supply a
141T uses, but I have never ever had fuses blow in otherwise in spec
equipment blow due to a surge other than nearby lightning hit. If the
fuses blow on rather commonplace power line voltage fluctuations, then
either the design choices for the fuses (or other things) were wrong
from day one, or something in your equipment is consuming too much
power -- either in normal operation, or on during startup transients.
Cheers, Kuba
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