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Best preamp for testing tubes

tombowlus

tombowlus

If it sounds good, it is good
Gold Supporting Member
Apr 3, 2003
35,516
19,950
North central Ohio
www.bassgearmag.com
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Editor-in-Chief, Bass Gear Magazine
#1
I have a pretty nice little stash of new and NOS tubes, most of which I have not had an opportunity to try. Now that I have a couple of tube preamps, I was wondering which one you folks thought would be the best for trying out various tubes. Ideally, I'd be looking for a preamp that allows the characteristics of the tubes to be heard (or not heard, as the case may be), and that does not add much coloration of its own. Ease of tube swapping would also be an appropriate consideration.

Here are the tube preamps that I have to chose from:

Aguilar DB 680
Aguilar DB 659
Eden Navigator
Alembic F-1X
Demeter VTBP-201s
Chandler Tube Drive
Tube Works Blue Tube

Alternately, I could use one of the following heads:

Eden VT-300A
Aguilar DB 359
Trace Elliot V8
Mesa Boogie Walkabout

The Navigator has never seemed very responsive to tube changes, so I am thinking that it is not the one to use. My only other semi intensive tube rolling was done with the Walkabout, and I certainly could hear small, but subtle differences in every tube. The 680 is a great pre, but it's got three 12AU7's and two 12AX7's, so it might be difficult to nail down just which tube was imparting which characteristics. The V8 has seven 12AX7's, so that's not going to help!

The Chander/Tube Works is nice, in that it is a fairly simple circuit path, and from past experience (with the Chandler), you really hear major differences between tubes. The downside is that these units are not designed primarily as bass preamps.

The 659 has been one of the preamps to respond the most dramatically to a tube change, but it does seem to have its own character. I guess I am leaning towards the Demeter or the F-1X at this point, with confirmation testing on the Chandler.

Any thoughts? If anyone is interested in hearing my thoughts on a particular tube in a particular amp, I can try and post a list of the tubes on hand.

Later, Tom.
 
#2
Tom;

I would use the Demeter. As I recall, Bass Player used to (and maybe still does) use the VTBP 201 S as a reference amp. Having said that, you won't really know what a tube will do for a given preamp 'til you try it because of differences in circuitry and all that.

Richard
 
#3
r379 said:
Having said that, you won't really know what a tube will do for a given preamp 'til you try it because of differences in circuitry and all that.
Click to expand...

Exactly, so my question, itself, may be an exercise in chasing one's tail, but I thought I'd ask and see if any of y'all had experience with a preamp (hopefully one I have!) which has - on the whole - proven to be fairly representative of what a given tube might sound like. And of course, much of that goes out the window when it comes time to actually put the tube to use in a given piece of gear, but at least this allows a kind of starting point (hopefully).

Thanks for chiming in, Richard.

Tom.
 
#4
r379 said:
Tom;

I would use the Demeter. As I recall, Bass Player used to (and maybe still does) use the VTBP 201 S as a reference amp. Having said that, you won't really know what a tube will do for a given preamp 'til you try it because of differences in circuitry and all that.

Richard
Click to expand...

that might work against him in this case though...the fact that the demeter doesn't color the tone much could also mean that it won't matter much which tube is used. i would think that a preamp with more coloration to the sound might be affected more by the tube used.
 
#5
Good point, I think. Testing tubes for tone where the only consideration is what the tester thinks about the tone makes it hard to do, doesn't it? No numbers to juggle. If I were going to be doing this it'd only be to find out how a given tube sounded in a given preamp. It gets a lot harder when you're trying to do a shotgun comparison. Having said that, I don't think the audiophiles test tubes in obviously "colored" gear unless you're going to define "colored" as gear they like vs. gear someone else likes.
 
#8
TaySte_2000 said:
Wouldn't the low down sound one be a very good one. Very easy to change the tube on it as well
Click to expand...

I am not familiar with this. Do you mean the LowEnd True-Voice preamp? This uses a 6SN7 tube, which, sadly, is not in my arsenal (mostly 12AX7's, 12AT7's, 12AU7's, 5751's, etc.).
 
#10
Another important point if you're going to do this, is that you should have an amp without a PCB-mount tube socket, or else at least one with upright tube orientation.

You start pulling and replacing tubes in the current cheap PCB sockets without tubeholders and you're going to wind up with a loose socket in surprisingly short order, loose enough for the tube to vibrate out if it's oriented downward.

On old flying-lead sockets with open backs, you could just peen over the contacts from behind to regain grip, but not on the current PCB sockets.
 
#11
r379 said:
Yer right, Tom. I was just about to edit my last post.

Edit: Wonder if one of the LowEnd units could be made/modified for that purpose?
Click to expand...

it wouldnt be to difficult to do this (though i doubt i could without proper research) but im sure if you talk to the builder he could build one with a 12AX7. IMO the sound of the 6S_7 is much better than the 12A_7.

im not sure if it would be possible, but it would be cool to have a pre with inputs for 12AX7, 12AT7, 6SL7, 6SN7, 12AU7 or whatever else inputs and a switch to change them.

when i think about it im sure that would entail extremely complicated and expensive wiring... oh well
 
#12
Get an adapter. IMHO the True voice would be THE best option for a quick changing bass oriented tube preamp. Granted - the adapter would be extra money but I think it would be worth it. And who knows maybe some members will kick some funds your way so you can post your findings. As for different preamps, well each unit will be different - but still have distinct tell tale characteristcs. Say you have a naturally bass preamp and you want to brighten it up. Just reference the findings from the TRUE voice sessions and the readers may have better ideas.
For a simple circuit - the True voice is probably as simple as it gets. i'd also like to know how much the tube in the true voice is driven - at realistic amp voltages and current or lower?

~Michael
 
#13
BassJunkie730 said:
Get an adapter. IMHO the True voice would be THE best option for a quick changing bass oriented tube preamp. Granted - the adapter would be extra money but I think it would be worth it. And who knows maybe some members will kick some funds your way so you can post your findings. As for different preamps, well each unit will be different - but still have distinct tell tale characteristcs. Say you have a naturally bass preamp and you want to brighten it up. Just reference the findings from the TRUE voice sessions and the readers may have better ideas.
For a simple circuit - the True voice is probably as simple as it gets. i'd also like to know how much the tube in the true voice is driven - at realistic amp voltages and current or lower?

~Michael
Click to expand...

I wonder if such an adapter would work? I'll have to ask Brian...
 
#14
Bongolation said:
Another important point if you're going to do this, is that you should have an amp without a PCB-mount tube socket, or else at least one with upright tube orientation.

You start pulling and replacing tubes in the current cheap PCB sockets without tubeholders and you're going to wind up with a loose socket in surprisingly short order, loose enough for the tube to vibrate out if it's oriented downward.

On old flying-lead sockets with open backs, you could just peen over the contacts from behind to regain grip, but not on the current PCB sockets.
Click to expand...

Excellent point!
 
#15
Another pre that I would consider using for testing is one of the few that I don't see in your arsenal - The IP777. The rear mounted tubes make it very easy to swap them and the tube holders in the back are very sturdy. It is by no means a "transparent" pre but it reacts fairly dramatically to different tubes which will give you a sense of relative differences.
 
#17
I have two. The first is the 201s. It's clear enough that you can hear the difference. Have you had a chance to work your's out yet ? What do you think ?

The other is a Bellari MP105. A little metal box with phantom power, phase reverse and gain. Wall wart driven. It's a very basic mic pre that sounds like crap direct from the store as they use some cheap- mo 12ax7. Actually sounds pretty decent with a decent tube in it. I use mine mostly to get a little more gain into a channel strip if I have a low output device that I'm attempting to record. In this case gain means gain, not distortion of course. There is very little worse or less useful than a mic pre that distorts in my book ...

Anyway I'm interested to hear your thoughts on the 201s.
 
#18
4Mal said:
I have two. The first is the 201s. It's clear enough that you can hear the difference. Have you had a chance to work your's out yet ? What do you think ?

The other is a Bellari MP103. A little metal box with phantom power, phase reverse and gain. Wall wart driven. It's a very basic mic pre that sounds like crap direct from the store as they use some cheap- mo 12ax7. Actually sounds pretty decent with a decent tube in it. I use mine mostly to get a little more gain into a channel strip if I have a low output device that I'm attempting to record. In this case gain means gain, not distortion of course. There is very little worse or less useful than a mic pre that distorts in my book ...

Anyway I'm interested to hear your thoughts on the 201s.
Click to expand...

My 201s is on its way to me from Joel, so I can't comment on it just yet. Hopefully, I will have it soon, though!

Tom.
 
#19
Joelc73 said:
Another pre that I would consider using for testing is one of the few that I don't see in your arsenal - The IP777. The rear mounted tubes make it very easy to swap them and the tube holders in the back are very sturdy. It is by no means a "transparent" pre but it reacts fairly dramatically to different tubes which will give you a sense of relative differences.
Click to expand...

Damn, you just had to say that, didn't you! :rollno:
 

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