Tu-be or not Tu-be
Questions and Answers on New Old Stock Tubes

Part 2 - Sonic Characteristics of N.O.S. Tubes

Sonically, can you make any generalizations about the sound of the various N.O.S. tubes made in the tube heyday of the 50s and 60s?

You can to a degree. When people think Mullard, they think of a tube that has a little bit more of a relaxed presentation- something a little more laid back. When I think of Telefunkens, I think of a very, very neutral tube with a beautiful midrange. Telefunken tubes always seem to work right. Of course, you have to be careful about making global generalizations like that. For example, the Telefunken 6DJ8 is a little more laid back on top than other tubes in the Telefunken line and the bass is not quite as deep and tight as some other 6DJ8 types, so I think you have to be careful when using that particular tube. Amperex tubes, depending on where they were made, typically will have a little bit more energy on top and will be very, very dynamic. It also kind of depends on the individual tube number that you are talking about. Amperex 6922’s and 7308’s are interchangeable electronically, but sound wayyy different in practice.

So, it is not necessarily correct to state that the "house sounds" of tubes produced by certain manufacturers run throughout their entire particular product lines…

Well- there might be a smidge of that, especially in the case of Mullards. Mullards seem to have kind of a relaxed, "everything is going to be okay" type of presentation. But beyond that, I like to make recommendations to people based on the individual tube- an earlier production Mullard 6DJ8 or 6922 is quite a bit different than the late production ones. Not just in the way that they sound, but also whether or not they are appropriate for different applications.

Do these generalizations hold true with power tubes as well as tubes typically used in preamps?

Power tubes are awfully difficult to talk about because there just is not a whole lot left. If you're talking about EL34s, Mullards or Amperex Bugle Boys made in Holland and the U.K. are the best. They're wonderful, they're relaxed, they're musical, and they're also almost impossible to find today. In 6550s, the absolute finest example of that tube would be the Tung-Sol. For the KT88s, Genelex is the best.

So premium brand N.O.S. power tubes aren't really a viable option for most audiophiles…

It's hard for me to recommend to somebody to dump that much money because a power amplifier is going to use typically at least a quad or two of tubes. Looking at the 6550's, with Tung-Sols running maybe $100.00 each, you are talking about a guy making an $800.00 investment. If you want the absolute best and have the time and funds to get them, by all means go for the N.O.S. power tubes. For those more limited in time and budget, I think it makes more sense to change pre-amp tubes by maybe upgrading a pair of N.O.S. 6922's or 12AX7's. Not only are these tubes less expensive and more available, I think that they offer even more benefits sonically that upgrades to N.O.S. power tubes. Preamp tubes also last longer, offering more bang for the buck.

Are the year or place of the manufacturer of a particular new old stock tube significant in terms of their sonic characteristics?

Yes, and again, the Mullard 6922 is a great example of this situation. The later model of this tube, called a CV2493, is a great tube. It sounds relaxed and extended, everybody loves them, nobody hates them except for one thing. This tube is unusually sensitive to vibration, so you can't use it in certain preamps such as an Audibile Illusions Modulus 3A, which feature a tremendous amount of gain. If your amplifier has a lot of gain and if your speakers are really efficient, Mullard CV2493's will start ringing. So that's why I don't like to say that there is any absolute, unqualified "best" tube … it depends on the individual component and everything else downstream. Some products are more sensitive to either noise or microphonics than others, so any N.O.S. tube decision must account for these factors. Ultimately, it's a matter of synergy.

Are their certain brands of new old stock tubes that the tube purchaser should shy away from?

Tough question. Let me answer by giving you another example. The early Raytheon tubes were very, very, very cool. Some of them were made by CBS. Later Raytheon tubes were all Japanese, which doesn't make them a bad tube, they are just completely different than what you might expect to find in the box. Same thing with certain Amperex boxes. There is a mark on some Amperex boxes that, when I see it, lets me know there may be trouble inside. I’ve figured out why, but will disclose that secret in the article I’ve written.

In a way, I think this question goes back to the bigger issue of "What is a new old stock tube?" Edicron, not to be confused with Ediswan, is a British company or at least they have a British address on the tube boxes, but inside you are going to find a Yugoslavian tube. I've received "Brimar" 6SN7GT's that are clearly made in Russia and Gold Lion KT88’s undoubtedly made in China. Unfortunately, the way things are today, the name on the tube alone will not always tell you the whole story about what you're buying.

Are there any keys for determining whether a particular new old stock tube would be right for a particular application?

Not in terms that can be described in a single paragraph- it really depends on the synergy of the system. Tubes can be used to address other areas that are a little bit forward or a little bit recessed in the audio spectrum. You can use a tube to fine-tune the flavor of your system if you have a problem area. If your system is a little bit lightweight in bass, if its a little tizzy on top, if its too soft on top, if it's too forward in the mid band, you can use tubes to help remedy those problems. But the correct tube decision is not going to be determined exclusively by the one component, it's going to be determined by the system.

A certain degree of care must be exercised in selecting N.O.S. tubes. Simply plugging an Amperex 6DJ8 into your system doesn't necessarily mean that it will suddenly come to life. In fact, your system can sound worse if you haven't accounted for the different characteristics and flavors of N.O.S. tubes. If you have a system that is slightly forward already and you think "I'm going to put new old stock tubes in, it's going to sound better", well, that may or may not be true. If you pick a tube that itself has a somewhat forward nature, then you've exacerbated the problem. So it's not a matter of just using new old stock tubes, it's a matter of using the right tubes.

Are there any information resources or printed materials out there that address and discuss the various sonic signatures of N.O.S. tubes? Is there a sourcebook or something like that that people can turn to for system matching help with N.O.S. tubes?

None that I'm aware of, unfortunately.

I know there are "heavy duty" versions of standard tubes out there, many of which built to military spec, typically bearing extra letters on the end of the tube label such as the "12ax7wa". Do these variants factor significantly in the tube selection process?

Not really. I don't think that's something people should worry about too much.

What is the advantage, if any, of gold pins on a tube?

The only real benefit of gold pins is that it keeps them from getting tarnished.

O.K., let's walk through a typical tube inquiry. Say a guy calls up and wants to try some new old stock tubes for his Audible Illusions Modules 3A. What type of questions would you typically ask him?

For starters, I’m an Audible Illusions dealer so I know that the Mod 3 has a lot of gain. Accordingly, I have to be very careful to sell him a tube that is not going to be sensitive to vibration. A tube that would be acceptable in other preamps may not be acceptable in a Mod 3, because if you hit the mute switch or turn the volume up and down, the wrong tube can feed back or ring through the system for a second. This doesn't mean that the particular tube is good or bad, but it does annoy people.

I try to explain what the expectation with a particular tube should be up front. If a Mod 3 owner insists on Mullard CV2493's, I tell him to expect some ringing. It’s the nature of the 6DJ8/6922/7308 family. If that phenomenon is unbearable, I try to suggest a tube that will not have a propensity to ring in that preamp. Beyond electronic mismatch problems, I ask about tonal balance, the brand and condition of the current tubes, the current sound of the system, and what the user wants to have happen.

So, for example, if the Mod 3 customer came to you and said his system sounded a little bit bright and he wanted to tone that down a bit, what would you typically suggest?

I would suggest an Amperex 7308, which is an excellent 6DJ8 variant. It has no sense of tizziness on top. It's not soft, but it's not tizzy either. It also has a smidge more bass than typical 68DJs and is very quiet.

And if the customer was looking to pump up his bass performance a little bit, how would you direct him?

I would still suggest the Amperex tube or a Siemens 7308. But the Siemens 7308 is also a little bit more forward in the upper mid range, which may create other problems.

If the system is soft on top, which isn't going to happen with the Mod 3A, I would recommend an Amperex or other Holland-made 6922. Those have a little more energy on top but in some systems they can end up sounding a little thin.

Ultimately, the decision depends on system synergy and the user's particular tastes. Some people may be unusually sensitive to hash on top while others want a little more zip because they are into rock and roll. The "right" N.O.S. tube for each of these people will be different.

...continued in Part 3 - Where to Find N.O.S. Tubes