6J6 dual cathode follower

[shooter]

I used a bunch of 7pin tubes, made a triplet SE 6AU6 amp, driven with a 6sn7(octal) and a 6j6 as cathode follower into the triplet, was a grungy sound susceptible to RFI.  I did come up with a question on the 6J6, dual triode that shares a cathode.  Can I use this as a dual cathode follower, mixer, 2 different signals into the grids, one common “mixed” signal out the cathode? 
Thanks

{edit-- split from parent thread, re-named -- PRR}

[sluckey]

I did come up with a question on the 6J6, dual triode that shares a cathode.  Can I use this as a dual cathode follower, mixer, 2 different signals into the grids, one common “mixed” signal out the cathode?

yes

[PRR]

Yes but... output level may be limited.

You may usually do better with a single triode (both-halves of 6J6 parallel if you wish) and mix-resistors into the grid.

"Triplet"?? Three 6AU6 'power' tubes parallel? Almost any plate-loaded stage can drive that. By the book you need 333K grid resistor(?). 470K will be fine. OTOH the plate of a 6J6 volt-amp can be under 5K.

[HotBluePlates]

... the 6J6, dual triode that shares a cathode.  Can I use this as a dual cathode follower ...

Tubes are designed with a specific purpose in mind. Pick a known-good circuit that connects the cathodes of 2 triodes.

Like a long-tail inverter. Or a differential amplifier. Or a tremolo oscillator (or trem buffer stage) cathode-coupled to a preamp stage.

A shared cathode implies only a resistance from cathode to ground for both triodes, because if you had a cathode bypass cap, the two triodes function independently. Maybe that bypass cap is a handy way for you to use these tubes if you wanted them for run-of-the-mill gain stages.

But if there is no bypass cap and the cathode resistance is not very small, increased tube current in one triode tends to cut current in the other triode. Which is how a differential-amp or a long-tail works.

I think that the shared-cathode-followers use of the 6J6 with have one triode's output fighting the other triode's output. But it should be breadboarded and tested to know exactly how it behaves.

[kagliostro]

I believe you can also use those 6j6's as PIs

Sure you can, here an example with 6J6 used in Floating Paraphase configuration

and one other where it is used as Long Tail PI

K

[shooter]

Thanks, I attached the "project", I ran preamp 2 into my Prow amp (quad SE el84) n had a couple gigging guitar guys play it n I got smiles! anyway I'm doing a multi pre build, still on paper and had 1/2 the 6j6 left over so I was tinkering with the idea of "blending" 2 signals.  N ya, I did put 3 6au6's in parallel into the standard champ ot that doug sells and loud level was about the same as a 5 watt'r.  Didn't work out the quirks but was happy with the build.