Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on August 09, 2016, 04:49:34 pm
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Hi guys, I have an amp that would normally have a 6BL8 in the PI position, but found a 6CQ8 instead.
http://www.nj7p.org/Tubes/PDFs/Frank/093-GE/6CQ8.pdf (http://www.nj7p.org/Tubes/PDFs/Frank/093-GE/6CQ8.pdf)
http://www.nj7p.org/Tubes/PDFs/Frank/127/6BL8.pdf (http://www.nj7p.org/Tubes/PDFs/Frank/127/6BL8.pdf)
They have the same pin numbers but one is a pentode and the other is a tetrode.
Similar but different???? :dontknow:
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post a schematic of the amp. It would be nice to know how the tetraode/pentode is being used.
The posted amplification factors of the triodes are different. How severe, not sure, remember, a lot of 12a_7 are used interchangeably.
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> Similar but different????
Exactly.
To the eye, that "tetrode" does not look like tetrode curves. No kink.
However the pentode will pull-down a bit more than the "tetrode".
Whether it makes a difference will depend a LOT on what the circuit asks of it.
If this a Dyna-like pentode voltage amp and triode cathodyne, it may make no real difference at all. Many Dynas are re-rigged each time the original recipe tri/pent becomes scarce.
When in doubt, put in the type the factory calls for. TubeDepot has it for $7.
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Schematic