• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6SN7 plate voltage, current and lifespan

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My PSU tweaking on my Aikido is reaping tangible results with regard to hum.

I added 30K across the final cap to bring current draw up to around 32mA, then added an extra 0.1uF to my PSU input cap (to give a total of 0.78uF on the tuning cap). Today, I will look for a 1uF motor-run cap as well as 80-100uF Motor-run caps for my filtering caps.

All of this brings me to questions of voltage, current, wattage and lifespan of my 6SN7GTA's.

I currently run the inputs at 4.5mA and the outputs at 7.2mA (or thereabouts). At it's present config, B+ is around 278VDC. When I do further tweaking with the "tuning" cap and maybe remove the 30K current sink, I expect that B+ will rise to somewhere in the region of 360VDC. Anyway, this would mean that each plate of my 6SN7's will be seeing 360/2 = 180VDC.

The tube specs give maximum ratings as: 450VDC per plate at 20mA cathode current with power dissipation of 5W for a single plate, 7.5W if both plates are used.

By my reckoning, if each plate does end-up seeing 180VDC, even at 10mA current, each plate would be required to dissipate around 1.8W. This is well within the tubes specs.

OK, I noticed when I added current-draw, that sonically, the amp, with 278VDC (as opposed to 317VDC) sounded a tad more sluggish - still amazing, but somehow the polish was dulled slightly. Sorry for the poor adjectives.

Now my QUESTION: with the high cost of NOS 6SN7s, to what degree does would running the tubes hotter (ie. higher wattage) effect lifespan? Of course, I am in no way going to get close to their max. I had read that many tubes were rated for 10,000 hours, is that running at max wattage?

Thanks,
Charlie
 
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