6BL8/6CQ8 Interchangeable

[TIMBO]

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/127/6BL8.pdf
They have the same pin numbers but one is a pentode and the other is a tetrode.
Similar but different????

[drgonzonm]

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.   

[PRR]

> 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.

[TIMBO]

Schematic