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SO I have this 1963 Bassman that had a Bias pot professionally installed. When I got it, it had Mesa 6L6GCs in it. I put a set of NOS Tung Sol 5881s in there and proceeded to re-Bias the amp.
I measured 420VDC on Pin 3 of the power tubes. The Tung Sol 5881 max plate dissipation is 23 Watts (http://lib.store.yahoo.net/lib/thetubestore/ts5881.pdf)
23 / 420 = .0547, so 54.7 mA
70% of 54.7 = 38.33 mA
With the tubes nice and hot, I measured before adjusting anything. I got 24.91mA
Turning the bias pot all the way clockwise results in a reading of 34.47 mA using my Eurotubes bias probe.
If my math is right, this translates to 63% of max plate dissipation, which seems kind of low.
What I'm confused about is that from what I've read, bias below 70% translates to more headroom, but if I reverse the math (.03447 * 420) I get 14.477 watts, which seems to indicate that I would get break up at a nice low volume.
Is that 14.477 watts per tube? That would make the amp 28.95 watts which makes way more sense...
Obviously I'm fuzzy on this stuff...
I measured 420VDC on Pin 3 of the power tubes. The Tung Sol 5881 max plate dissipation is 23 Watts (http://lib.store.yahoo.net/lib/thetubestore/ts5881.pdf)
23 / 420 = .0547, so 54.7 mA
70% of 54.7 = 38.33 mA
With the tubes nice and hot, I measured before adjusting anything. I got 24.91mA
Turning the bias pot all the way clockwise results in a reading of 34.47 mA using my Eurotubes bias probe.
If my math is right, this translates to 63% of max plate dissipation, which seems kind of low.
What I'm confused about is that from what I've read, bias below 70% translates to more headroom, but if I reverse the math (.03447 * 420) I get 14.477 watts, which seems to indicate that I would get break up at a nice low volume.
Is that 14.477 watts per tube? That would make the amp 28.95 watts which makes way more sense...
Obviously I'm fuzzy on this stuff...