Heptode preamp

[Arthur Dent]

I have an old amp that had a 6AU6 preamp pentode, and it sounded completely amazing, though very noisy. I had swapped that tube out for a 6BA6, which sounded similar with a little less noise.

Then, I found something interesting: a 6BE6. It is a seven-pin heptode, which I found had a pinout and specs which would allow it to be directly swapped with the pentodes. I tried it of course, and it sounded even better in my opinion, and the amp is now dead quiet!

I have never heard of that being done, so I just wanted to pass on that tip to anyone who may be interested.

[Alex/Tubewonder]

That's analogous to strapping pentode as triode. Heptode strapped as pentode. How did you wire grid 3?

[Rob Mercure]

If you like your current result try using these bottles to mix two signals - much more elegant than the junction of two isolating resistors. Better yet try a 6L7 - if the grid cap isn't off putting - specifically desinged for audio work as a mixer/control tube.

Rob

[Arthur Dent]

Alex, grid 3 is jumpered to the cathode. I've never used a heptode before, so I didn't know what else to do with it. I guess it's supposed to be a second control grid, but I am unsure as to how I could use that beneficially. Wire it to grid 1?

Rob, that's a good idea. I haven't had any reason to mix two signals yet, but I'll keep that in mind.