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In Reply to: RE: Tube/Valve Lifespan posted by 6bq5 on December 10, 2020 at 20:40:13
"If the tube is biased hot, then start the subtraction machine..."
What would constitute a hot bias?
February 26, 2020: "You have fifteen people, and the fifteen within a couple of days is going to be down to close to zero,"
Follow Ups:
It really depends upon the tube -
and in truth it is not just the bias - but the power you are pushing into the tube to get the amplified music out-
Tubes have design specs - and generally they should be adhered to
There are designers who have pushed the ratings and get long life, there are others who push the envelope and get short tube life-
The Tube specs are not always easy to decipher-
From the RCA RC-30 Tube Manual- for the 6CA7 - Class A, Plate voltage, 800v, bias current 150mA
but in the next section, Class AB1 - Plate voltage 450, with a 'zero-signal plate current' of 120mA - which is the bias current w/o signal- or idle current...
So in a PP Amp using this tube - running a bias current above the 120mA would be 'hot' at a plate voltage of 450
But class AB1 is a bit of a sliding scale - and the place on the scale is determined by the bias current....
As with a sailboat, the design is a compromise.
For a sail boat, the line goes: Speed, Comfort, Sea-worthyness - pick two!
Happy Listening
I'd be lying to you if I said that I understood that . . . .
But I do like the way that they sound.
7-5-2019 "Our army manned the air, it rammed the ramparts, it took over the airports, it did everything it had to do, and at Fort McHenry, under the rockets' red glare, it had nothing but victory."
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