Gentlemen,
There always seems to be much talk about inrush current being detrimental to
tube filaments, light bulbs, etc. How many of us have turned on a cold light
bulb and have it blow open the filament? A power amplifier's filaments can
draw in excess of 15 steady state amps and much more cold. In tube circuits
the inrush filament current can hasten the life of a tube, some of which can
be rather expensive. Of course a thermister in series with the filament can
alleviate this problem, but it poses other problems, such as increased heat
(especially bad in Florida). If you turn the system on-off-on, the fuse most
likely will open because recycling of the thermistor is slow.
So I am searching for alternate ideas to the thermistor. The HV is no
problem because I simply add a 555 timer that shorts out a power resistor in
series with the B+. The relay activates after the tubes safely warm up.
I've posed this question on my beloved NG, RAT with little satisfaction. I
believe the problem is that this is an electronic, not tube problem. All
suggestions are very welcomed and appreciated. Thank you very much in
advance for you time.
Cordially,
west