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Re: Tube lifetime

Posted by dave slagle (M) on January 10, 2002 at 09:09:14

In Reply to: Tube lifetime posted by Paul Joppa on January 9, 2002 at 22:18:32:

very interesting...

i wonder if he was referring to all tubes or just IDT's ??

steve bench is a large proponant of starved filaments in DHT's

http://members.aol.com/sbench102/dht.html

i suppose they are looking at two different aspects tube life vs. linearity???

as an interesitn side, i have been looking briefly at voltage drop Vs. current in damper diodes, and some really strange things happen when you get to low currents say less than 10ma in some of them.

the 6DA4 has a voltage drop that increases linearly from 1ma on, while the 6Cm3 and thew 35CE3 both show positive voltage drops at 1ma, and then at some point go to 0 drop and then the "linear" voltage drops start at 5ma or so??? a very interesting thing is reducing the filament voltage by 25% completely eliminates this behavior in both of these tubes???

my only guess is the two tubes that show the peculiar behavior have double the filament power and current handling than the 6Da4 along with a much smaller voltage drop... and the "positive voltage drop" is from too large of a space charge in relation to the potentials??? it seemed that i could get down to about 50% on the filament voltage and still retain linear operation, an interestingly enough as we would expect the voltage drop goes up as the filament current goes down... for example, at 30ma the 6cm3 drops 1.1V 6.3V, and 1.8V at 3.5V... maybe a really cool way to tweek the bias on an input tube???

also maybe looking at the sub 1ma range on the 6DA4 might reveal a similar non-linear behavior?

dave

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