6BN11 vs 6CB6

[rsumperl]

Greetings everyone,
Based on the 2 data sheets, how close would you say these pentodes are, obviously leaving basing and single vs dual behind.

http://www.scottbecker.net/tube/sheets/093/6/6CB6A.pdf

http://www.scottbecker.net/tube/sheets/123/6/6BN11.pdf

Thanks,
Ray

[Wavebourn]

Similar non-linearity, but quite different transconductances.

[smoking-amp]

Take a look at 6EW6:
http://scottbecker.net/tube/sheets/093/6/6EW6.pdf
and 6LT8:
http://scottbecker.net/tube/sheets/135/6/6LT8.pdf

[rsumperl]

My goal was to find dual pentodes in one pkg. Basicly a compactron. I was hoping to sub them in the circuit that the 6CB6 uses in the red board.

Ray

[smoking-amp]

Change pot R52 to 150 Ohms approx. and the 6BN11 gm will be lowered to the 6CB6 range. You figure 1/gm to get equiv. resistance of the cathodes, then take the difference to get the compensation resistors. Since the CCS is running at 17 mA (8.5 mA per tube) you would strictly speaking have to figure the tube gm at this current for both tubes. This can be roughly approx. by using gm_new = (Inew/Iold)^.66 * gm_old, applied to each tube's datasheet values.

Or leave R52 the same and the open loop gain will be a bit higher.

Main issue with the dual compactron will be the inability to match the tube sections. So some adjustment of screen V or g1 bias may be advisable for one side. The pot (R52) does allow some adjustment for matching, but it changes AC gains as well as DC op points. Better to have a DC adjust and an AC adjust.