2. amps-preamps
  3. 1201324454

Best small signal tube for a preamp?

Is there inherently a "best" small signal tube for use in a preamp? Assuming all other things are equal-which of course they never are.
Choices are 6922/12AT7/12AU7/6BK7/6BZ7/12BH7/6H30II (and varients to the listed tubes - e.g. E88CC for 6922, etc.).
The reason for my question is that I am auditioning the Lector Zoe, which can use all of the above tubes by way of its SATC ( autiomatic tube adaptation) circuit and user switchable 6V/12V plate voltage.
I am interested in your reason, which might have to do with inherent sonic characteristics, predisposition for problems such as noise or microphonics, or availability and economy of NOS tubes being better for one tube type over the others. All responses are welcome, and in return I will let you know the results of my listening with the different tubes that I try.
mitch2
cyclonicman
693 posts
 
You may want to consider that many of these tubes have different load and gain levels and are not always interchangeable, even though they may look the same. If your preamp wiring cannot handle a load increase, you may incur some damage. For example, a 12AT7 and a 12AU7 look identical, however the 12AT7 has a gain of 60, while the 12AU7 has a gain of 19. If your preamp circuit was built for a 12AU7 and you retube it with a 12AT7, you are increasing the load gain to your preamp by over 300%.
mitch2 OP
3,966 posts
 
Cyclonicman, I appreciate your comments but the Zoe is specifically made to operate with the range of tubes listed above. The preamp has a SATC (automatic tube adaptation) circuit and user switchable 6V/12V plate voltage, and the owner's manual specifically lists the tubes I listed above as all being compatable. One just has to remember to switch to the appropriate voltage, although yes the gains are different for the different tubes. Right now it sounds very good with some RCA 12AT7 black plates installed. I am still interested in trying a pair of premium NOS 6922 tubes, and currently looking into different sources.
keshiri
11 posts
 
Upscaleaudio.com has some premium (and expensive) 6922's in stock which you might want to check out. My Siemens 12AT7 has opened up nicely and is more fluid now as it's breaking in. I think I'll give tube purchases a break now as I can see myself living with this one for a while...
Did you notice an improvement upon reversing your speakers' leads?
keshiri
11 posts
 
Mitch2, I've read those old RCA 12AT7 blackplates are also very good. With the ZOE, are you finding that you're turning the volume dial to around 3 o'clock for reasonably loud volume levels, as I'm finding with my 12AT7s? I rarely had to turn it past 12 o'clock with the 12AU7!
mitch2 OP
3,966 posts
 
Hi Keshiri, I still don't have the "feel" of the Zoe, and honestly have not paid too much attention to where the volume knob is set. It is a very nice preamp, and an absolute steal for the price, and I compared it head to head with the Vibe/Pulse. Interesting about the black plates, I have a special pair of them (blessed by monks or something) from Brian at AAudio in my CD player and they sound great. This pair in the Zoe was originally a little noisy in the CD player, but are absolutely quiet in the preamp. Maybe they were not seated properly in the player. I have only used the AT7's and the original 6922's in the preamp, but it seemed the 6922's had a bit more drive, and the AT7's are a bit richer and sweeter sounding.
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