[roymail]

12AX7 = 100 x gain
12AT7 =  70 x gain
12AU7 = 20 x gain
7025 = 100 x gain

I copied this from a thread in another circle.  Blair, would you mind briefly explaining the advantages of using each of these tubes.  I still have much to learn.  Thanks! 

[djbnh]

You could also add using 5751 v. 12AX7.

[avahifi]

My info is that the 5751 tube is a ruggedized, but lower gain, version of the 12AX7 tube designed for portable radio use.

We used them many years ago when good new 12AX7 tubes were simply not available.  We found an adequate supply of NOS GE5751 tubes that were better than available alternatives.

Now, with several brands of new good 12AX7 tubes available (we use JJ 12AX7/ECC83s types in certain circuits) I see no reason to switch to 5751 tubes. However, the higher gain of a good 12AX7 tube may cause high feedback transcient overload in some circuits and the use of a 5751 might then provide slightly milder, but less defined musicality.

It all depends upon the circuit design of course.  It really is nice to know what the circuit really wants before just trying different tubes.

Regards,

Frank Van Alstine

[Niteshade]

My personal favorite (meaning most used) out of what you have as options is the 12AU7. I use it in preamps and amps. I hardly ever use a 12AX7, however, Fisher did with great success in the 500C tube receiver as a phase splitter.

[roymail]

My personal favorite (meaning most used) out of what you have as options is the 12AU7.

Blair, I know it's not the list, but I read somewhere that a 6SN7 has three times lower distortion and three times the drive capability of the 12AU7.  Is this correct?  I'm just wondering if it would be a good choice for the Beacon One?

Of course you understand the circuit and I don't, so I'm just asking. 

[Niteshade]

Distortion and sound quality are mainly derived from the circuit which drives the tube. I was listening to a Beacon One yesterday using a 12AU7 and thought it sounded absolutely wonderful! The circuit is a moderately low voltage/low impedance type that doesn't stress the tube at all and can drive just about anything.

I am making Beacon One's with 6SN7's too.

[Freo-1]

Distortion and sound quality are mainly derived from the circuit which drives the tube. I was listening to a Beacon One yesterday using a 12AU7 and thought it sounded absolutely wonderful! The circuit is a moderately low voltage/low impedance type that doesn't stress the tube at all and can drive just about anything.

I am making Beacon One's with 6SN7's too.

Agree with 12AU7.  I have a small cache of Raytheon and Westinghouse NOS and ANOS Black Plate tubes for my preamp section, and they sound wonderful.  Also have some NOS Tung Sol D getters 12AU7 tubes, and they are very nice performers.

My amp uses 12AX7 as the driver tube, and I love the sound from them.  Have a pair of Raytheon US Army NOS from 1948 that are incredible.  Also have some NOS Japan from the early 60s that are a well kept secret.  (Very quiet and non microphonic)

I HATE the 6DJ8/6922/7308 tubes for audio.  They CAN sound excellent, but they are WAY too prone to microphonics and noise.

[Ericus Rex]

I HATE the 6DJ8/6922/7308 tubes for audio.  They CAN sound excellent, but they are WAY too prone to microphonics and noise.

That's been my experience too.  Happy to now not have any 6DJ8s in my sys.

Freo, come one man!  Spill the beans on that secret Japanese 12AX7!

[Niteshade]

Bottom line: If the circuit keeps the tube happy, you're way better off!

Preamps and amps that chew up tubes are best for recycling material.

[FullRangeMan]

Anyone knows what is the sound character of the 12SN7 ??
It is the same sound of the 6SN7 ??

[Freo-1]

That's been my experience too.  Happy to now not have any 6DJ8s in my sys.

Freo, come one man!  Spill the beans on that secret Japanese 12AX7!

No secret really.  They are marked Raytheon from 62 to 64 date codes.  One is marked USA, one is marked Japan, but they are identical.  They are the early Raytheon Japan, with shiny flash vs. the caramel colored ones the later tubes from Japan exhibit.  They have a 2 digit code on the bottom of the glass.  They are DEAD quiet, non microphonic, very neutral. 

[roymail]

Distortion and sound quality are mainly derived from the circuit which drives the tube. I was listening to a Beacon One yesterday using a 12AU7 and thought it sounded absolutely wonderful! The circuit is a moderately low voltage/low impedance type that doesn't stress the tube at all and can drive just about anything.
I am making Beacon One's with 6SN7's too.

Blair, thanks for your comments.  Does the Beacon One using the 12AU7 in the circuit add any tube character to the overall sonics when driving an SS amp?

[6L6PPP]

They are exactly the same only the filament voltage is different. I have 60 or so 12SN7s (RCA/ KEN RAD/ SYLVANIA/ HYTRON etc...) and the equivalent 6SN7 sounds the same. The tube I really like is the 7AF7 or tall bottle 7N7 with an adapter.

Anyone knows what is the sound character of the 12SN7 ??
It is the same sound of the 6SN7 ??

[FullRangeMan]

They are exactly the same only the filament voltage is different. I have 60 or so 12SN7s (RCA/ KEN RAD/ SYLVANIA/ HYTRON etc...) and the equivalent 6SN7 sounds the same. The tube I really like is the 7AF7 or tall bottle 7N7 with an adapter.

6L6PPP,
Much Thanks for your reply, I appreciated it.   I will study the 7AF7 & 7N7 too.
Best Regards