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In Reply to: RE: look even closer... posted by Steve O on March 22, 2017 at 15:22:09
I am not sure that that 8W is reasonable whilst the anode is run to 25W. The g2 grid posts are equipped with radiators at the top, which could allow this. U-L seems to leave EL34's run at high voltage to push their screens into having glowing spots, which is not what I'd call ideal.
While taking on design work in the past, U-L curves are not very much more linear than the pentode curves, though these curves have only been published at AB1 voltages. That would require a significantly higher load than is available to achieve Class A operation, and for that I will cap reasonably available at 10k a-a.
IMO, the primary benefit to U-L is a reduction in device output impedance; the plate resistance is lower...:) The next time I have the hoods up on my 813 monoblocks, I am going to run them full pentode, with their g2 at B+, with the plates i*R of the OPT primary less. Dropping the g2 voltage as current goes up *WITH THE 813* at 600V is not quite optimal. Or I will put them back to running the 4E27's...LOL
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
...Problems can occur if all max ratings exist simultaneously: 800V/25W anode, 500V/8W g2 but that's far from the case here. Also note that these values are from the conservative "Design Centre" rating system, not today's more prevalent "Design Maximum" system . FWIW, data sheet calls out 30W combined anode+g2 in triode mode @ 500V. Overall, since subject amp is ~ 450V, 33W seems a reasonable max rating and 30W a conservative one.
Bottom line is that 24W in a 9 is a safe and conservative value.
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