[Amps] Dimished Tube Life

[Dennis OConnor]

What kills tubes in the amateur service is turning the amp OFF - period...  
The absolute worst thing you can do is cycle the power... In my shack on weekends the amp is turned on on Friday night and left on until Sunday night..
The commercial service folks reduce the filament voltage about 15% when in stand-by to enhance tube life - up to ten times... You do not want to reduce it too much as there is a penalty for passing up and down through the Miller-Larsen grain reorientation temperature...  So, if tube life is a concern, then put a resistor on the primary with a relay and switch, and drop the filament voltage 10-15% when not using the amp...  With such a setup, tube life could be in the 50,000 to 80,000 hour range, or up to 10 years of continuous power-on...

Now, those figures are derived from VOA experiments for directly heated tungsten filament cathodes... Indirectly heated cathodes operate a bit differently and often the emitting surface wears out before the filament breaks, but the basics still apply... Lower the heat when in stand-by and the indirect surface emits fewer electrons extending its life - as well as the filament's.

Lastly, you need to calculate the cost of the electricity to power the amp for 80,000 hours and decide if the tubes or the electric are the cost limiting items...

As far as transmitting with lower filament voltage - be aware that you can poison the filament... I had that happen with an expensive 3CX-1200 when the filament voltage went lower than was safe due to the power company playing games with the line voltage between day and night...  TAASTAFL

denny / k8do