[Herbie]

Some amps have lots of output power tubes.  A pair of Cary V12 monoblocks uses 24 output tubes, each prone to microphonic distortion to some degree. A pair of Atma-Sphere MA-1 monos uses twenty-eight 6AS7 tubes, a pair of MA-2 monos uses forty. We have one customer with eighty-four 6AS7 output tubes in his audio system. Another uses an UltraSonic Damping Instrument on each of two hundred and forty KT-88 tubes in his home theater!

The cost of damping microphonic vibrations in so many tubes can do quite a job on the bank account. The investment is worthwhile, considering that damping instruments will bring out more of the full potential of the much larger cost of the tube gear itself.

With a limited budget or frugal approach, it always makes sense to damp source and small-signal input/driver tubes first, and most importantly, any rectifier tubes. It needn't necessarily break the bank, however, to damp the power tubes also and reap the additional sonic rewards.

I have found, as have many of our customers, that damping every other stereo pair of output tubes often achieves a sufficient and desirable level of damping. Keep in mind, properly designed damping instruments damp vibrations and subsequent distortion--not the music itself. What we've found is that with amplifiers having many output tubes, damping half of them seems to achieve substantially more than 50% of the benefit you would get by damping all of the power tubes.

1/2 = more than 50%. This is a purely subjective analysis, but when it comes to listening and enjoying music, the subjectivity--how well you enjoy the music--is all that really matters. Damping half of the power tubes by placing damping instruments on one stereo pair and then skipping one pair, etc., allows the inherent "flavor" of the tubes to come through unfettered, yet keeps microphonics from muffing things up.

Of course, if you should try this and feel you want to go even further in the same sonic direction, there's nothing wrong with damping all the power tubes. As a matter of frugality though, if you have eight or more power tubes, you might try damping just every other pair--you'll likely find that to be sufficient and completely enjoyable.

Best regards,

Steve Herbelin
Herbie's Audio Lab

[rockadanny]

I've always been afraid to put anything on my tubes for fear of the restricting material possibly causing unnatural stress on the expanding glass, lessening its life. Perhaps causing fractures or weakness in the glass. Can this happen?

[Herbie]

Hi, rockadanny. Herbie's vacuum tube dampers all have plenty of flex to accommodate any glass expansion, and open-air designs allow for natural cooling by convection. We believe that optimal tube life is extended by damping bulb vibration. This has been demonstrated and proven with ordinary light bulbs, which are vacuum tubes. Although there seems to be little empirical data, plenty of anecdotal evidence supports this to be true also with audio tubes. Regardless of whether usable tube life is extended, though, music will almost always sound better with reduced microphonics.

Vacuum tubes tend to become more sensitive to vibrational distortion as they get older. Little parts inside are all directly or indirectly coupled to the tube glass, so reducing vibration at the glass also reduces vibrations internally. It seems likely that reducing the vibrational environment of the tube has potential to prolong the structural integrity of the internal parts and keep them sounding like new for years and years.

Steve
Herbie's Audio Lab

[rockadanny]

Steve - Thank you for the reply. Can you please explain how your product works vs. black or orange o-rings I see on some tubes? I believe some of the orange o-rings I've seen come from car headlight parts.

[zybar]

Steve,

Funny that you mention a pair of Atma-Sphere MA-1's...those are my amps.   

I use your dampening devices on the 5 6SN7 tubes per MA-1 monoblock, but have never tried your products on the output tubes because there was too many of them.

Maybe now I will think about it.

Thanks for posting.

George

[Herbie]

Hi, again, rockadanny. This and many other questions regarding UltraSonic Damping Instruments are discussed on our website:

UltraSonic FAQ's
 
High-temperature silicone O-rings can be beneficial to a degree, but usually entail some sonic trade-off. Because of the highly vulcanized nature of these rings, they are prone to rubber-like resonances and rubber-like sonic influence.
 
Some users have reported noticeable muddiness, loss of midrange information, and/or "peaking" at certain bass frequencies. O-Rings placed around tubes have no structure to disperse vibrations. By contrast, UltraSonic Damping Instruments disperse vibrations via isolation pads into their surrounding "C" rings. Having open ends instead of being a closed loop, a C-ring will diminish vibrations to a degree that a solid O-ring will not.
 
UltraSonic Damping Instruments more effectively eliminate unwanted vibration while remaining linearily neutral and faithful to the source signal.
 
Orange-red O-rings like those sold on ebay as tube dampers and similar black O-rings included with some manufacturers' tube gear do not hold up to some hot-running power and rectifier tubes for the long haul. These O-rings can fuse to power tubes or eventually crack and wear out. "Aerospace High-Temperature Silicone" handles ambient temperatures up to 450° F for a good while, but continuous radiant heat from output and rectifier tubes (which generally run about 480° F) will gradually plasticize the silicone and render it useless. They are inexpensive enough to replace every once in a while though, and often provide satisfactory relief for guitar amp tube rattle issues. These O-rings hold up very well with cooler, small-signal preamp tubes, but generally provide only minimal benefit. If you want to bring out more of the inherent potential of your tube gear, UltraSonics are in a different leaque altogether.
 
Steve

[rockadanny]

Thank you again Steve. Excellent. I will seriously consider these for (2) 6SL7s (power amp inputs); (2) 6SN7s (power amp drivers); (2) 6SN7s (preamp linestage); and a 6X5 (preamp rectifier).