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

Showing 6 responses by keshiri

keshiri
11 posts
 
I have a Zoe, and have acquired the following tubes thus far:

Sovtek 6H30pi
NOS Mullard 12AU7
NOS Siemens 12AT7 (early '60's)
NOS Sylvania 6BK7B

The Sovtek was warm, smooth and too weighty, and lacked some focus, detail, and dimensionality. I wouldn't say it's accurate.
The Mullard was a fantastic all-rounder. Rich & nice balance, but I was looking for more punch and midrange clarity. I'm now trying the Siemens. It's not yet broken in (20 hours or so). I'm very impressed so far. Very quiet, more 3d, solid bottom, and slightly more air, although w/ some grain and not as rich as Mullard's midrange (maybe after a few more days?). I've not yet tried the 6BK7B. About the others, I'm not sure if 6BZ7 is worth a try (the only one I can find is $8 a pair though), and I've read that the 12BH7 and 6922 are not low in microphonics and were not originally designed for pre-amp use... so I'm leaving them for later.
One odd thing I noticed when changing from 12AU7 to 12AT7 was that I had to turn the volume dial 40% higher with the 12AT7 to achieve similar volume levels. I was under the impression the 12AT7 tube has about 40% more gain than the 12AU7. So shouldn't it mean I should be turning the volume dial down instead? Anyways, I'll let you know when the Siemens has fully broken in.

Also don't forget the Zoe is a phase-inverting pre-amp, so you should reverse the polarity of your speaker cables (on one end) for optimum sound. Cheers.
keshiri
11 posts
 
The manual doesn't say anything about phase inversion, and I don't have testing equipment to be 100% sure, but the Audiogon fellow I bought it from actually tests and writes technical papers for Soundstage magazine, so I'm taking his word for it. I'm very pleased with the Zoe, as it's right at home (center of it really) with the rest of my system, each costing more than Zoe.
I've read that NOS Amperex Bugle Boy 7AU7/7AT7 are some of the best. I'd love to also give Telefunkens a try. Can get used for about 1/2 price, which might be good as they usually have twice the life of others...
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!
keshiri
11 posts
 
After some more testing, I've found the Siemens ECC81 (12AT7) lacked some bass punch with most jazz & rock, and compressed at normal to higher volume levels. As you'd suggested, it may be due to lack of gain with 12AT7 in the ZOE. I put back the 6H30 but it was the same story: too much weight, not much detail, and very noisy. I'm now trying Mullard's ECC88, which is same family as 6922. It's similar to their 12AU7 but more space and midrange resolution, and the gain seems right: I don't need to turn the volume up more than half way.
This leads me to believe that 12AU7 and the 6922 family work best in the ZOE, as their gains seem right in my setup. I'm curious to hear how the Amperex 6922 sounds in this pre, so please do let us know. It seems the US-produced white-labeled PQ is the one audiophiles all over are after.
BTW, my system:
Wadia 830cdp
Technics 1200 tt
Plinius SA100MK3 power amp
Reference 3A Veena speakers
keshiri
11 posts
 
Wow Mitch I'm glad your Amperexes are working great because I ended up checking for some last week (tube rolling's enticing) and got a decent deal at Ebay for a pair of NOS US Jan white label Amperex 7308 (from 1966). Can't wait 'till they arrive. I hope they're similar to the 6922 white pq's as I also like the rich /full sound. My Zoe's owner's manual states the unit is originally furnished with 12AU7, which I find also works well. Have you found the ideal tubes for your Lector cdp? Lector's upstream gear are obviously giant killers. I wonder how their power amps sound like. I'd love to get my hands on their phono stage, which apparently costs more than the ZOE...
More to discover