12BH7 as preamp tube - any experiences?

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I've recently acquired a small horde of 12BH7 tubes for a good price, but I actually have no idea what to do with them... They were just intended to be spares for a Blackstar HT-5, although it now seems I have enough to last several millennia.

I know they make beastly little output tubes, but has anyone ever used them as pre-amp tubes? I'm contemplating a medium gain build with these things, the only problem being... I have no idea what to expect... I guess if it sounds like ass I'll just replace it with a 12au7

[Chuck H]

I'm contemplating a medium gain build with these things... I guess if it sounds like ass I'll just replace it with a 12au7

Ha. I have bucket full of 12au7's that test good pulled from an old Conn organ. And I too have been thinking of how to use them.

IMHE 12bh7's used as small signal amplifiers tend to be quite microphonic. But I was using a small bag of test good pulls when I determined that. They should be good as reverb drivers, cathode followers and maybe even concertina type splitters. And of course, small power tubes. Driving a pair of bugger bottles for an AB2 circuit maybe? I know there could be a miller capacitance issue but a mini "Marshall" with four 12bh7 power tubes sounds like a fun project.

OOOhhh... Here's an idea I've been wanting to try. Build a small AB1 amp, run it into a dummy load and re amp it with a big MOSFET amp. A perfect way to get real power amp clipping at any volume and the ability to run effects post distortion.

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I've heard that the NOS variants of the 12BH7 are hugely microphonic compared to current production... which sort of sucks because the stash I have were pulled from old TV sets I might just stick them in a couple of my existing builds and see how bad it really is.

[Diablo]

I kind of doubt that the NOS 12BH7 would be inferior to current production, although I haven't done any direct comparisons. NOS tubes were state of the art when tubes were dominating the electronics world. I've been using a NOS 12BH7 to tame the reverb driver in a BFDR, and it works just fine.

[Chuck H]

I've been using a NOS 12BH7 to tame the reverb driver in a BFDR, and it works just fine.

How are using that tube to "tame" the reverb driver? Isn't the BH good for almost twice the power of an AT? Also, unless you change the little transformer the load is grossley wrong. I suppose if you just stick one in there it would produce less drive if only because it's operating so far out of spec. I might use that tube to beef up the reverb drive. Way overkill for a BF Fender though as they get pretty wet stock.

[Diablo]

How are using that tube to "tame" the reverb driver? Isn't the BH good for almost twice the power of an AT? Also, unless you change the little transformer the load is grossley wrong. I suppose if you just stick one in there it would produce less drive if only because it's operating so far out of spec. I might use that tube to beef up the reverb drive. Way overkill for a BF Fender though as they get pretty wet stock.

I think the reason the 12BH7 tames the reverb is because it is a medium-mu (16.5 = amplification factor) vs the 12AT7 (amp factor = 60). The 12BH7 is capable of higher current, but in this case it's being lightly loaded and should last a very long time. Stick one in a BF Fender and see what you think.

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I've tried a some 12BH7's in a 12AU7 slot (it biases about right this way, plus the gain is similar), and they sound kind of similar. They don't sound half bad when overdriven. Microphonics aren't as bad as I expected, tapping on it obviously produces a response, but seems fine in normal operation. This might be due to the fact that they're further down in the chain of tubes though (literally the last gain stage before the PI). I'm thinking of cranking up the B+ to 400v and running them at max dissipation, albeit in a pre-amp configuration. Might sound interesting. I've got a ton of these things to 'burn' through... so to speak

[J M Fahey]

For me, tubes are tubes. If I had 100+ of*any* tube, I´d design something around them and turn that into cash.
I bought 1000 *CC189 (mostly "E", the rest "P") for peanuts, I´m doing exactly that.
No, they were not used by Leo nor Jim nor are endorsed by any Guru and no, I´m modding no Classic circuit for them, too different fom a 12A*7.
Why do that anyway?
But the datasheet allows me to design working, overdrivable gain stages.
Real tube distortion for those who care about it.