Dual-control, sharp-cutoff pentode

[rsumperl]

Good afternoon everyone,
In a pentode that advertises as a dual-control, sharp-cutoff pentode and that G1 and the suppressor grid, G3 can be used as control elements, if G3 is grounded, does this pentode then act like any other pentode? Specifically I am looking at the 6BV11.

Thanks
Ray

 

[smoking-amp]

You need a positive voltage on grid3, like +8V, to get them to behave like a normal pentode:

curves:
http://www.diyaudio.com/forums/tubes-valves/160240-suppresor-grid-used-feedback-6.html#post2083612

https://frank.pocnet.net/sheets/123/6/6BV11.pdf

0 V on g3 causes a large % of plate current to be reflected back to g2. With +8V on g3, most of the current goes through to the plate like a normal pentode. The resulting lowered g2 dissipation should allow the plate diss. to be increased, maybe to 3.5 Watt each. (typical 4:1 rule, 1 Watt less grid 2 diss. allows 4 Watts more plate diss. The plates look more than twice the size of the 3.1 Watt 6BN11 dual P) Should make a decent dual pentode tube with g3 at +8V. Grid 1 gm typically doubles with the g3 mod too (for dual control tubes, more cathode current makes it to the plate). Both tubes on the $1 list.

..

 

[rsumperl]

If applying 8V to G3, would you go through a 1K or so resistor? Would you bypass G3 with a cap to ground?

Thanks

You need a positive voltage on grid3, like +8V, to get them to behave like a normal pentode:

curves:
http://www.diyaudio.com/forums/tubes-valves/160240-suppresor-grid-used-feedback-6.html#post2083612

https://frank.pocnet.net/sheets/123/6/6BV11.pdf

0 V on g3 causes a large % of plate current to be reflected back to g2. With +8V on g3, most of the current goes through to the plate like a normal pentode. The resulting lowered g2 dissipation should allow the plate diss. to be increased, maybe to 3.5 Watt each. (typical 4:1 rule, 1 Watt less grid 2 diss. allows 4 Watts more plate diss. The plates look more than twice the size of the 3.1 Watt 6BN11 dual P) Should make a decent dual pentode tube with g3 at +8V. Grid 1 gm typically doubles with the g3 mod too (for dual control tubes, more cathode current makes it to the plate). Both tubes on the $1 list.

..

 

[smoking-amp]

The gm for grid 3 is only 400 on the datasheet, so a grid stopper should not be needed. And the current for G3 is minimal. The R - C would still help to keep out power supply noise though.