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RE: EL34 - second class tube?

Mike:

I don't find the reference you linked particularly credible WRT vacuum tube design and production parameters.

FWIW, here's why I believe the 6L6=hard vacuum/EL34=soft vacuum is urban myth BS: One of the insidious consequences of gas in a vacuum tube is detrimental g1 current. The most common means of dealing with the potential for g1 current is to specify a relatively low value of g1 max resistance. If one looks up the max specified g1 resistance for a 6L6 one finds 100K ohm for fixed bias operation. Max specified g1 resistance for the EL34 at similar operating conditions is typically 500K: considerably higher than the max for the 6L6. Based on these specs alone, theoretically I'd conclude that the 6L6 is more prone to g1 current than the EL34. Considering the usual cause of g1 current, by inference the 6L6 is the tube with the soft vacuum, not the EL34 as that guitar amp publication asserts. Practically, I'd expect that the degree of vacuum is equal for both tubes within the limits of normal mfg tolerance.

Overall, I think the author of your linked reference is commenting more on the differences in breakup characteristics betw a beam tetrode and a true pentoad.

Is my logic wrong? If so, got any other sources of the hard/soft vacuum claim?

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