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Registered Member #2318
Joined: Fri Aug 28 2009, 01:22AM
Location:
Posts: 33
I finally got my first VTTC working good. I am using two 572b tubes. I have seen on several youtube videos where people will slowly turn the filaments of the tubes on rather than switching them hard on and off. I understand that logically this will extend the life of the tubes because it puts less thermal stress on the filaments. But realistically am I going to see a much shorter life from them by just turning them on and off? If so then I need to add in some way to gently turn them on which I have not done yet. Just wondering if it is worth the trouble. Thank you!
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Because of the way the resistance of the filaments changes with temperature, using a constant current source rather than a fixed voltage will give you a gentler switch on. The switch off is less traumatic anyway.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Civil and military medium power transmitters of the Thermionic Age commonly had a "Heaters On" switch or a "Standby" fulfilling the same function.
More sophisticated designs used time delay relays, such that the HT would only be connected to the valves in question after so many (RC time constant) milliseconds.
In maritime mobile and military applications dependent on 12V Lead-acid batteries, the question about whether to have the power hungry heaters on all the time (as in 'Standby') was an important one stretching further than the stress damage caused by applying HT to a valve before it has reached its correct operating temperature.
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How critical is it to "baby" vacuum tubes? Am I going to kill my tubes turning them on and off?
