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In Reply to: RE: PSVANE 2A3C x Shuguang 2A3C, what is the best ? posted by Aldovan on June 03, 2015 at 19:52:07
...I am a complete convert to the JJ 2A3-40. Well worth the price difference.
Follow Ups:
This JJ have 40W dissipation.
What power you can obtain ? 8W ?
Its not a question as to how much Power Out the JJ can do, but rather, how nice it sounds for the first 1 Watt of use, where I would listen 99 percent of the time on Altecs, or any high efficiency speaker system.
Jeff Medwin
...the maximum power output from the JJ will be about the same as any other 2A3, that is about 4W in class A1 (no grid current.) According to its specifications the JJ 2A3 can be run at 300B operating points (but still 2.5V across filament) which could indeed yield around 8W, or perhaps a little more, in A1.
Class A2 operation (grids swinging positive and drawing current) may permit higher power output but requires a driver stage designed for that purpose. I have no idea how the JJ compares to other DHT tubes in supporting such operation. Most tube manufacturers don't draw plate curves for positive Vgk.
Generally, if the tube is designed for A2 it will say so clearly - there must be allowance for heat dissipation from the grid, so the mechanical design is different, and you will sometimes see a spec for grid dissipation.
A few older tubes were operated in push-pull A2 or B2 without any specific design features; the 45 is the most well-known example. I suspect that the circuits used (e.g. a 56 into a 1:1+1 interstage transformer)were not capable of driving enough current to do much damage.
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