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In Reply to: Re: 7241, 7242 posted by Lew on October 20, 2004 at 08:24:16:
The 7241 has 3 cathodes and 3 heaters - not really all that different from a scaled-up version of the 6336A, [most versions of] which have 2 cathodes and 2 heaters.The problem is the same that exists with the majority of pass tubes: notoriously mismatched sections.
In my experience, the 7241 is no worse than either the 6336A or the 6AS7 in this regard. In general, one has to either abandon the idea of paralleled sections/tubes or else accept these limitations.
The WE 421A is an exception to this rule.
BTW: I've never used [or even seen] the 7242.
Follow Ups:
"In general, one has to either abandon the idea of paralleled sections/tubes or else accept these limitations."Why couldn't one just redesign the circuit to allow for biasing each tube section separately? Just as in most conventional transformer coupled amps that used multi output tubes.
Tre'
I think I can answer for Jim, since he e-mailed me privately with a pdf for the 7241. Each tube has 3 heaters, 3 cathodes, ONE grid, and ONE plate, so I don't think one can externally correct for internal imbalance, if one cathode is current-hogging for example. However, I have built my Atma-sphere MA240s such that I can individually bias each of the six output tubes (currently 6C33Cs), so perhaps I can use the 7241 if I can find enough tubes that are reasonably internally balanced. (By separate biasing I can to a degree compensate for differences between tubes.)
Yes, with only one grid and one plate my idea would not work....
Tre'
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