Stereomour Tube Equivalents

[Grainger49]

This thread is getting started to explore tube types, different numbers, that can be used in the Stereomour without any circuit modifications.  That is, drop in equivalents.

These are the ones I have found.  Variants like a 12AT7A will be in parentheses.  I will modify the OP with others as posters contribute other numbers.

If anyone finds that I have a tube with the wrong pin out, or higher heater current than the Stereomour can supply please post and I will modify the OP accordingly.

Stereomour Tube Equivalents (in numerical order):

12AT7(A, WA, WC)
6060 (Brimar number)
6679
B739
CV4024
ECC81
ECC801(S)
6201



2A3
2A3C
2A3-40

[balancedtriode]

i got a genalex gold lion  B739
sounds amazing with the stereomour and has become my first choice for the driver tube
i highly recomend it it sounds great and its not nearly even burned in yet

[Grainger49]

Thanks for the first response to any of the equivalent tube threads I started.

I have not heard of a B739 and checked on the Duncan site PJ linked below.  It is good!

Again, thanks!

[Thoburn]

Do you think a 8526 would work (replacing the 12AT7)?

[Paul Joppa]

Do you think a 8526 would work (replacing the 12AT7)?

Not without major circuit changes. Look at the critical parameters, 12AT7 to 8526:

Plate resistance 10900 vs 4000
transconductance 5500 vs 5000
gain (mu) 60 vs 20

You have to match ALL those parameters, within normal variations (20 percent?), to have a viable substitute.

Also, the 12AT7 operates at around 230v on the plate. The 8526 has a maximum voltage of 165 volts.

Here's a link to Duncan Amps:  http://tdsl.duncanamps.com/
Look under "tube data" to find links to data sheets for most tubes. I could not find the 8526 there, or at another site I often use, but the 1973 GE handbook lists it, and that book is available as a reprint - I got my copy from Antique Electronics. Sometimes you have to scounge around for information on ancient technology like tubes!

[Thoburn]

Ouch! That is quite a different tube. The only reason I posted is that I have a pre-amp where the final output tube can be either the 12AT7 or the 8526. In that pre-amp the 8526 was more lively. I really need to learn more about tube gear. Anybody know of a good book for an electronics dolt?

[Doc B.]

Ouch! That is quite a different tube. The only reason I posted is that I have a pre-amp where the final output tube can be either the 12AT7 or the 8526. In that pre-amp the 8526 was more lively. I really need to learn more about tube gear. Anybody know of a good book for an electronics dolt?

I'm chuckling, as it sounds like maybe the guy who designed your preamp is the one who needs to learn a little more about tube gear. Tube choices are actually a fairly advanced topic since there are lots of parameters to consider. I would suggest starting with something like an RCA tube manual, which has some pretty good chapters on tube applications along with the tube data. Also, check out Pete Millet's site. He has done the community a great service in gathering all sorts of useful publications about vacuum tubes.

[Maxwell_E]

i got a genalex gold lion  B739
sounds amazing with the stereomour and has become my first choice for the driver tube
i highly recomend it it sounds great and its not nearly even burned in yet

I'm curious, is that a NOS B739, or one of the reissues that they've started making again?

[balancedtriode]

its a NOS but i recently bought a new stock one
it sounds great as well not as great as the NOS but it has not burned in yet so the jury`s still out

[Thoburn]

Do you think a 8526 would work (replacing the 12AT7)?

I screwed up big time. The tube I ment is a 5751. Not a 8526. I don't know where I got the 8526 from. Very sorry for the mistake.

[Paul Joppa]

The 5751 is also very different from the 12AT7 - plate resistance is 58K vs. 10.9K for example. In my opinion, it can barely drive a 45 satisfactorily, and does not have the drive for a 2A3. It is much more similar to a 12AX7. The 5751 will not work in Stereomour at all unless the plate current is reduced to half (2mA) and the bias is reduced to around 1.5v - perhaps an LED would work.

[Thoburn]

Oi Vay. Thanks PJ. I dug my old pre-amp out of the closet. It was using that tube instead of the 12AT7. I confess to knowing nothing about matching tubes. Can't say why that tube works in the 12AT7's stead. The pre-amp is a Basie that stock uses 3 12AT7 tubes. One tube left and the other right. Both feeding the third tube. It works with a 12AT7 or the 5751 in the third socket. I found the 5751 to be more dynamic that the 12AT7 in the third spot, but can obviously give no reason for it.

[Paul Joppa]

... One tube left and the other right. Both feeding the third tube....

It's probably a cathode follower output, which has fixed voltages so it can be more flexible about tube parameters. It's much harder to guess why it might sound more dynamic; but the difference in operating conditions is large enough that it could be that, rather than any sonic differences between the tubes, which causes the perceived effect.

[Dyna Saur]

12DT8 is also a nice 12AT7 replacement, with the limitation that the 12AT7 filament power is 12.6V AC (or DC) . I recently built a small 12B4A SET, which originally had a 12AT7 for the VA tube, and seeing that the 12DT8 has the same operating characteristics, I decided to give it a try, and was not disappointed!  

In my small amp, the B+ voltages are significantly lower, about 250VDC for the 12B4As, and 220VDC for the 12AT7 / 12DT8, so this tube  may or not be equally  applicable to the Stereomour, with its higher plate supply  voltage and current.

FWIW, the RCA 12DT8 which I used  has "ribbed plates" similar to some of teh 12AX7s, but smaller dimensions.

6679 is also another "industrial numbered"  12AT7 equivalent. This series continues with 6680 (12AU7A) and 6681 (12AX7A)


/ed B in NC

[Grainger49]

So I should toss in 12DT8 in the top?  I have 6679 now.

Thanks Ed!