Q: What's the advantage of Herbie's dampers over other kinds of tube dampers?
A. Here are some observations we've made:
Duende Criatura Tube Rings: Although these European rings are great at bringing out a sense of detail and clarity, they don't fully reveal the deeper "texture" of each note, and lower/mid frequencies seem a bit thin at times. To keep tubes from overheating, they should be placed near the top of the tubes where they are sometimes least effective. Though sonically competitive with Herbie's original PTFE HAL-O tube dampers, these tube rings lack the punch, microdynamic speed, and nuance of Herbie's newer damping instruments. They're not bad dampers overall though, delivering an overall pleasant result.
Pearl Tube Coolers: These heat sinks are designed to keep tubes a little cooler, potentially extending tube life. Without ample ventilation though, they cause tubes to run hotter! Then again, with ample ventilation, there's no need for coolers, because natural airflow convection does the job. At controlling microphonics, they are marginally effective when new. Rubbery O-rings holding the heat sink against the tube gradually become brittle from the heat though, resulting in gradually increasing, uncomfortable distortion. Audio vacuum tubes are designed to operate within an elevated temperature range (that's why all have internal heaters); artificially lowering a tube's operating temperature would achieve no sonic benefit and could be audibly detrimental.
Tube Anchors/Brass Rings: Though awkward to work with, Tube Anchors by MapleShade are excellent sonically, the only dampers we have tested that play in the same league as our damping instruments. Massive brass clamped around a tube, however, deprives the glass bulb of air ventilation needed for cooling. Our tests with brass Tube Anchors resulted in fairly cool-running input/driver tubes running an average of 33.8º F hotter than without Anchors. Other manufacturers make brass or copper sleeves and deceptively imply that they are tube "coolers." They are not.
Absorb-Gel (Allnic): These are extension sockets with a gel material inside. We have found that damping tube sockets can sometimes be effective at reducing microphonics, but damping the bulb glass is much more effective and the results more consistent amongst various tubes and components. Damping the socket and tube both can be mutually effective; placing a ring of Permatex Blue Silicone Gasket Maker (available at auto parts stores) around tube sockets dampens them quite effectively, without the drawback of having an additional set of pins/sockets for each tube, keeping a more direct electronic signal intact. (Because Allnic Absorb-Gel Dampers damp vibrations under the tube pins, the benefits are minimal compared to damping the socket directly contacting the tube pins.) In almost all cases though, Herbie's damping instruments provide optimal results without having to worry about damping the sockets.
Cool Damper by EAT (Euro Audio Team): Herbie's Audio Lab has tested this fine-looking tube damper and found it to be a bust. These dampers reduce tube microphonics, but the sonic result is poor. Lower midrange frequencies are bland; acute dynamics tend to be "rounded" without energetic attack and decay; high frequencies are well-represented, but lack many of the intangibles that give a sense of live performance. As coolers, they fare even worse. Although the damper appears to be designed as a heat sink, the thermally conductive interface between the glass bulb and aluminum fins is woefully inadequate for the device to function as such.
Tube Sox: These are woven tubes made of fiberglass-like Kevlar that slip over your vacuum tubes, reducing microphonics somewhat effectively with minimal attenuation of some higher frequencies and some loss of inner detail. They become stiff with age, due to UV radiation and heat, losing their flexibility and damping ability. No-brainer verdict: not a good product.
Neoprene and nitrile O-rings help microphonics a little, but after a while these materials get brittle from tube heat and the rings become ineffective. Their relatively high durometer (hardness) limits their ability to absorb subtle vibration in the first place. After all, like other O-rings, they're made to be used as seals, not as vacuum tube dampers.
PTFE-coated silicone O-rings fare better. These industrial seals, available from McMaster-Carr and other hardware suppliers, tend to improve the sound of tubes suffering particularly from microphonics or tube rattle, adding only a slight frequency coloration. Some users have reported satisfactory results with these. With some tubes, however, they induce a bloopy, muddied bass and/or high-frequency loss and/or upper-mid harshness. Because PTFE softens and elongates with higher temperature, results can be unpredictable when in direct contact with the radiant heat of tube glass.
Elastomer O-rings: Such as silicone, 3M and Audio Research tube dampers. Silicone o-rings can work pretty well at reducing vibrations, but some users have reported noticeable muddiness, loss of midrange information, and/or "peaking" at certain bass frequencies. Elastomer rings can fuse to power tubes or eventually crack and wear out. O-Rings placed around tubes have no place to disperse vibrations; by contrast, all Herbie's dampers feature isolation pads to absorb and disperse vibrations into their surrounding "C" ring.
Caution: silicone O-rings like those sold on ebay as "tube dampers" do not hold up to some hot-running power and rectifier tubes for the long haul -- "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.
Sorbothane: Sorbothane is heat resistant only to 200° F. (93.5° C), after which the material melts. According to Sorbothane's website data, the material begins losing its vibration-absorbing ability after reaching a temperature of only 160° F. With cool-running tubes that it can be used with, Sorbothane tends to cause "bloopy" bass and attenuate the higher frequencies. (Herbie's Audio Lab highly recommends that Sorbothane be used absolutely nowhere in an audio system. This material will often achieve a localized sonic tradeoff that seems beneficial, but literally contaminates the sonic integrity of the system as a whole.)
Shun Mook resonators: These are small African blackwood (Mpingo) discs placed on the top of tubes. Unlike Gabon ebony, which smooths out acute microphonics, Mpingo (not an ebony, it's of the rosewood family), produces a vibrant resonance that can enhance a recording's sense of vitality. Subtle effect can be system dependent and subject to personal taste/preference. At Herbie's Audio Lab, we believe that reducing microphonic distortion to unveil the energy and spirit of the original recording session is a more honest, and ultimately more effective, approach.
DIY: Here are a few do-it-yourself alternatives:
Wire twist ties wrapped with PTFE tape (the kind of tape used to wrap pipe threads). This "damper" can achieve a worthwhile, though minimal improvement. Many tweakers use PTFE tape alone, without wire, just wrapping tape around the tube. Although this microphonics remedy doesn't bring out the highest potential in your tube gear, results generally are acceptable for the price involved and will rarely do any harm sonically.
Automotive heater hose or PTFE shrink wrap surrounding tubes. Sometimes improves the quality of badly microphonic tubes, but insulates the tubes, causing them to run hotter than they should. Can make excellent-sounding tubes sound worse. Oftentimes causes "bloopy" or choppy bass, weird highs.
Mortite: Rope caulk is a great vibration-absorbing material for use with internal component chassis, loudspeaker baskets and many other applications (and highly recommended by Herbie's Audio Lab). Not advised for vacuum tubes, however. Mortite and other brands of rope caulk have a high temperature range of only 150°F (66°C). The material might hold up to the heat of small-signal tubes for an audition or two (which will probably yield good sonic results), but before long, Mortite will turn foamy, smoke and burn, partially vaporize and melt into a pathetic mess (similarly, Blu-Tak has very poor high-temperature range and will melt readily on vacuum tubes).
Babbitt putty, a high-temperature material (978°F) with some qualities similar to Mortite, can be used effectively on vacuum tubes and yields excellent sonic results, but exudes an offensive odor.
Oil-filled bottle. Effective? perhaps. Practical to use? perhaps not.
Herbie's Tube Dampers:
UltraSonic SS, originally introduced as a lower-cost alternative to UltraSonic Rx for small-signal tubes, UltraSonic SS has incrementally improved to where it now equals Rx in sonic quality. Delivers a pure and unblemished audio result.
UltraSonic Rx: The sonic result with a highly resolving audio system can be uncanny. It's the closest we've experienced to being in a recording studio monitoring an actual performance "live" or being in the presence of a live event.
Guitar Amp UltraSonic, designed to minimize microphonics, oscillation, and tube rattle in severe vibrational environments as found in a combo guitar amp. Works superbly with home audio systems as well, delivering a highly linear and spacious soundstage with plenty of "air" and detail.
HAL-O III: Herbie's newest, this all-titanium stabilizer improves the performance of the very best vacuum tubes while faithfully preserving the audio system's unique character. Recommended for rectifier tubes and for all extremely hot-running tubes.