Hi,
I built a Simple SE with a JJ ecc99 driver tube a couple years ago. I used the ecc99 because I have an active tube preamp that I like, so I didn't want as much gain as the 12AT7 would have given me. I changed one resistor (R13) to get ~20 mA of plate current from the CCS, otherwise it's the same as on the schematic.
The datasheet below has data listed with and without shield, are they referring to the internal shield that separates the triode halves? If so, does the shield exist in all 12BH7 tubes? I just want to make sure I'm not wasting $ on a nos 12BH7. Thanks!
http://www.classiccmp.org/rtellason/tubedata/12BH7.pdf
I built a Simple SE with a JJ ecc99 driver tube a couple years ago. I used the ecc99 because I have an active tube preamp that I like, so I didn't want as much gain as the 12AT7 would have given me. I changed one resistor (R13) to get ~20 mA of plate current from the CCS, otherwise it's the same as on the schematic.
The datasheet below has data listed with and without shield, are they referring to the internal shield that separates the triode halves? If so, does the shield exist in all 12BH7 tubes? I just want to make sure I'm not wasting $ on a nos 12BH7. Thanks!
http://www.classiccmp.org/rtellason/tubedata/12BH7.pdf
Dave,
I have many NOS American 12BH7/12BH7As in my personal stock. These include RCA, GE, Sylvania, Tung Sol, CBS and some Euro types like Amperex and IEC Service Master. None of them has an internal shield. In fact, I can't remember ever seeing one that did. Curiously the data sheet you linked to is a "tentative" one. I suspect a shield was never really used, or so few times that I've not seen one. Also, the RCA and GE tube manuals do not mention any shield.
I have many NOS American 12BH7/12BH7As in my personal stock. These include RCA, GE, Sylvania, Tung Sol, CBS and some Euro types like Amperex and IEC Service Master. None of them has an internal shield. In fact, I can't remember ever seeing one that did. Curiously the data sheet you linked to is a "tentative" one. I suspect a shield was never really used, or so few times that I've not seen one. Also, the RCA and GE tube manuals do not mention any shield.
I've got a small assortment of 12BH7, and I've never seen a shield in any of them either.
There is a curious evolution in these small triodes. As best I can gather first there was the 6J5, which is a single low-mu triode in octal basing. Then there is the 6SN7GT, which looks like two 6J5 in one bottle (still octal). Then came the 6CG7 which appears to be a direct descendant of the 6SN7, except it came in the nine-pin base and has the shield between the triodes. I think they later discovered the shield really wasn't necessary and eliminated it in the 6FQ7. Otherwise, all these guys are nearly the same (at least on paper).
Next up we've got the 6GU7 and its twelve volt brother, the 12BH7. These two are not electrically identical to the first bunch, but certainly close enough that drop-in replacements usually work just fine. These tubes seem to have a strong reputation as superior alternatives to one of the more common low-mu twin triodes. Which brings us to the last, and arguably the least: the oft-maligned 12AU7. Again it's characteristics are not exact matches for either of the first two groups, but close enough. I guess the biggest thing it has going for it is sheer volume of production. There's a boatload of 12AU7 out there.
Assuming you can manipulate the base and wiring, and you've got enough heater current available, I'd think any of these tubes could be made to work in the same circuit. Some should clearly work better than others, but they should all work.
There is a curious evolution in these small triodes. As best I can gather first there was the 6J5, which is a single low-mu triode in octal basing. Then there is the 6SN7GT, which looks like two 6J5 in one bottle (still octal). Then came the 6CG7 which appears to be a direct descendant of the 6SN7, except it came in the nine-pin base and has the shield between the triodes. I think they later discovered the shield really wasn't necessary and eliminated it in the 6FQ7. Otherwise, all these guys are nearly the same (at least on paper).
Next up we've got the 6GU7 and its twelve volt brother, the 12BH7. These two are not electrically identical to the first bunch, but certainly close enough that drop-in replacements usually work just fine. These tubes seem to have a strong reputation as superior alternatives to one of the more common low-mu twin triodes. Which brings us to the last, and arguably the least: the oft-maligned 12AU7. Again it's characteristics are not exact matches for either of the first two groups, but close enough. I guess the biggest thing it has going for it is sheer volume of production. There's a boatload of 12AU7 out there.
Assuming you can manipulate the base and wiring, and you've got enough heater current available, I'd think any of these tubes could be made to work in the same circuit. Some should clearly work better than others, but they should all work.
The reason i ask is, I was told the 12at7 (that the Simple SE uses in stock form) has a shield that allows the triodes to operate independently. One triode for left channel, one for right, and the shield would keep one channel from affecting the other. It looks like the pinout for the at7 is the same as the bh7, so I'm guessing that I was misinformed regarding the shield in the at7 and the bh7 should work fine in the Simple SE in place of my current jj ecc99.
Is this the case or am I missing something? Thanks for your patience
Is this the case or am I missing something? Thanks for your patience
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Wow, forgot about this thread.
I spent $20 or so on a NOS RCA 12BH7 and it was money well spent. In fact, it's still in there driving a pair of Winged-C EL34s and I haven't touched my system all year. It's still running 20 mA plate current on the BH7 and all has been good using the amp several hours a day.
The synergy between this amp and my Omega single drivers is amazing, I have never been happy with my system for longer than a couple months and while my system could be improved, it is finally to the point where it doesn't annoy me and on some material is actually really good.
So, if you don't need the gain of an at7 the bh7 seems like a good option. The gain structure works out pretty good with this driver tube and an active preamp.
I spent $20 or so on a NOS RCA 12BH7 and it was money well spent. In fact, it's still in there driving a pair of Winged-C EL34s and I haven't touched my system all year. It's still running 20 mA plate current on the BH7 and all has been good using the amp several hours a day.
The synergy between this amp and my Omega single drivers is amazing, I have never been happy with my system for longer than a couple months and while my system could be improved, it is finally to the point where it doesn't annoy me and on some material is actually really good.
So, if you don't need the gain of an at7 the bh7 seems like a good option. The gain structure works out pretty good with this driver tube and an active preamp.
If a valve has a shield, make sure it can be grounded either to ground or a cathode. Failing that, the grounded end of the heater. A floating shield can cause all sort of weird problems unless it is kept strictly well away from the electrons (e.g. no anode holes facing the shield). There was a thread on here about this a few months ago.
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