12BH7/12BH7a subs?

[pstamler]

What about a 12FQ7 or 12CG7, basically identical to 6SN7 except for basing and heater voltage/current? They're a lot more linear in most configurations than 12BH7s. Or are they also just as hard to find where you are?

Peace,
Paul

 

[NewYorkDave]

6FQ7 and 6CG7 are the more common 6V-heater versions. They're good tubes, similar to 6SN7 as Paul says. Or, if you don't mind an octal, 6SN7 is still common and cheap.

Using two 12AU7s is possibly the best idea yet. AU7s are easy to come by, and should remain so for at least a few years to come. In at least a couple of "classic" designs--don't recall exact models at the moment--I've seen two AU7 used where one might have usually found a single BH7, CG7, etc. These were push-pull plate-loaded circuits.

 

[CJ]

OK, the AU7 was stuck in the BH7 socket on the LA2 last night and I could hear no difference. I did the swap about ten times. I wish I had an A/B switch, as you lose a little focus waiting for the tubes to warm up, but still, I heard no major difference. Both tubes run pretty cold in the LA2, as Dave says, they are not really being hit very hard in that circuit.

If anything, I noticed a bit more detail with the AU7. So, good to know. If you have a bucket load of AU7's and don't want to hassle buying the BH7, you should be OK for the LA2 at least. I did try using the LA2 for driving a Pultec (600 ohm input iron), and did not notice any ill effects.

One useful DIY project would be a 9 pin plug that you plug into the tube socket. Then, you would have two 9 pin sockets mounted on a board with a switch for going between the two for comparisons. This would save the tube socket from wear and tear, and also eliminate warm up time. Leave the heaters on, just switch the B+ back and forth.

BTW: Interesting to note that the LA2 will still pass audio with the 12BH7 removed, reminding us that the last stage is indeed a buffer stage that does little in the way of amplification.

 

[SUPERMAGOO]

can i find bh7!!! and test my la2 w/ au7 and bh7.i feel beter bh7....
6cg7 I´ts the same than bh7 but diferent heater???.
good info.thanks to all!!!

 

[pstamler]

[quote author="SUPERMAGOO"]can i find bh7!!! and test my la2 w/ au7 and bh7.i feel beter bh7....
6cg7 I´ts the same than bh7 but diferent heater???.
good info.thanks to all!!![/quote]

No, 6CG7 is the same as 6SN7/12SN7/6FQ7 in terms of tube characteristics. The 12SN7 has a 12V 0.3A filament, the two *SN7 tubes are octal while the *CG7/*FQ7 tubes are 9-pin miniature. All are hefty medium-mu tubes. with perhaps more oomph than the 12BH7 and certainly better linearity in most applications. I originally recommended the 12FQ7 as a plug-in sub for the 12BH7 because its filament is compatible; my guess is that it'd do a good job as a substitute, possibly with a couple of resistor changes.

Peace,
Paul

 

[SUPERMAGOO]

pstamler:thanks.

 

[ciminosound]

Oh yeah, I just remembered someone told about the 6GU7 as a replacement for the 12BH7. Different heater voltage of course. The characteristics look nearly identical. Check it out and comment if you would.....

http://www.pmillett.com/tubedata/HB-3/Receiving%20Tubes%20Part%202/12BH7-A.PDF

http://www.pmillett.com/tubedata/HB-3/Receiving%20Tubes%20Part%202/6GU7.PDF

 

[CJ]

Pretty darn close spec wise. The GU7 curves llok a little more bent, but that might be a good thing.

Darn, I just threw out about ten of those things to make room in my tube caddy for more glassware. :evil:

Wasn't the GU7 used in a Gibson amp or something?
Seems familiar.

 

[bovox]

Hey, did anyone react on the newrope E80CC? I notice that it has a lower
Ua max 300V. And not so much of Na, just 2W per system, but...
I´ts a bigger tube, it needs double the heat current and I´ve seen it and
listen to it (EMT 140 tubeplate-amp -converted into a Mic-amp with a
optocompressor between the 2 stages.) It sound nice and huge.
My question is; have anybody used it as a WCF??
Cheers Bo