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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Re: Balancing preamp warm up with tube life posted by Ron Oehlert on April 2, 2006 at 10:45:26:
Some modern tube preamps run the tubes a bit hard. These designs will often consume preamp tubes at a faster rate than a standard Dynaco PAS2/3 Preamplifier.If the preamp is tube rectified the start-up sequence will not be as hard on the tubes as designs with solid state rectification and low value series resistors in the power supply.
Some diode rectified supplies employ a larger voltage dropping resistor so that the voltage rise will not be as sudden as with some supplies that provide B+ seconds before the filaments have a chance to stabilize.
In either case the dominant issue is standing current and plate dissipation (limiting tube life with the Preamps left on always) and the other extreme where the frequency of power cycling stresses the tube and causes them to fail prematurely.
The final parameter that can have a deleterious effect of tube life is the filament voltage. If too high then the filament lasts for a shorter time. Usually the trick is to feed the tubes at of slightly below rated filament voltages. For 12AX7's this can be 6 to 6.3 Volts and 12 to 12.6 Volts. Anything in between I consider ideal.
Going over 6.3 and 12.6 Volts will cause the tube filament to glow brighter than usual and shorten tube life by a percentage between 3 and 10%, sometimes higher with Power Tubes.
Tube life is about balancing all parameters so that the circuit and tubes perform consistently over their expected lifetimes.
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Follow Ups
- Re: Balancing preamp warm up with tube life - shermanr@prw.net 14:37:26 04/03/06 (0)
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