|
While the Arthur Loesch audio designs are famous for being straightforward and natural sounding, a simple way to modify the sound to one's individual taste is by swapping or "rolling" the tubes (valves). By trying different brands or types, it's often possible to fine tune your component to the room, the recording, or other associated equipment.
The Amplitrex AT1000 Vacuum Tube Test System
Relatively new to the market, the AT1000 computerized analyzer may represent the last word in tube testing. Once a tube is selected from the internal data base, there are no more dials to fiddle with and the tube can be analyzed under real world conditions (up to 500V @ 160mA), a limitation of most vintage testers. When plugged into a personal computer, curves can be plotted and saved, new tubes can be added to the data base, and labels with all of the measured parameters can be printed out. Production is limited and there is a two to three month wait for delivery, but this one is on our short list of equipment upgrades.![]() Read the manual here: Microphonics The RCA Radiotron Designers Handbook (4th Edition) says, "There is no published standard test for microphony outside of Service or manufacturers' specifications... In radio receiver factories the valves are usually tested in the chassis in which they are to operate, the set being tuned to a signal generator with internal modulation, and the volume control set at maximum. Any microphonic sounds which quickly die away are not considered as cause for removal of the valve, but a sustained howl is so considered. Such a valve may not be microphonic in another position in the chassis or in another model of receiver. "Not withstanding the considerations above, all valves cannot be expected to be non-microphonic when placed directly in the acoustic field of, and close to, the loudspeaker in a receiver, particularly in a small cabinet." Tube broker Kevin Deal of Upscale Audio writes, "Tubes can have easy or hard jobs. If the tube is used to amplify [a] signal, then it is expected to make noise if tapped on. If it is used in other positions, then it may make no noise no matter how hard you tap on it. That's why you should never tap on tubes. It can damage them, and there is no benefit to doing it." To paraphrase, he continues to say that there are some tubes that sound nice, but which are sensitive to going "ting" for a moment, if tapped. These slightly microphonic tubes can actually add a sense of "air" or depth to the soundstage. The evidence is that when you test tubes from the same batch and manufacturer and find a pair that measure identically, save that one exhibits zero microphony, and then compare them by listening in an audio circuit, the non-microphonic tube often does not have the aural qualities that many prefer. For this reason, removing tube dampers (if you happen to use them) may actually improve the sound and that is why we don't recommend them. The bottom line? Small signal tubes are naturally microphonic, so don't get too neurotic about it. Goop Be careful about using goopy contact enhancers. We're not talking about cleaners and plating protectors, like the DeoxIT products mentioned above, but substances like Walker Audio Extreme SST or Xtreme AV Quicksilver. While the idea of filling in the rough (on a microscopic level) metallic surface of a tube pin to improve its conductivity is certainly valid, most of these products are electrically conductive (actually considered a selling point). Applied too generously, they can get into the wrong places on your tube or its socket, bridge the pins, short out the tube, and possibly the equipment it's plugged into. Is it worth the risk? Cryogenics Finally, a note on cryogenics, a treatment that changes the molecular structure of metal by extreme deep freezing. Is it the "last word" in enhancing your audio tubes or simply an excuse to relieve you of more money under the guise of science? Personally, we don't use or recommend cryogenically treated tubes, mainly for two reasons. The first is philosophical: As with $1,000+ AC power line cords, if you can hear the difference, then there may be something wrong with your component's design to begin with and you're simply adding a very expensive filter to a fundamentally flawed piece of equipment. The second is technical: A proper cryogenic treatment requires specialized equipment and has to be performed under very controlled circumstances. Otherwise, within six months the treatment will wear off, leaving the object as if it had never been treated in the first place. Can you tell if your tube was properly treated? Probably not. While there are proven benefits to cryogenically treating certain metallic objects for scientific or everyday use, we have yet to be convinced that there is any benefit to this when applied to vacuum tubes in home audio. Judge for yourself, but caveat emptor. |
| Tube Guide to the Tempo Electric Phono + Line Preamplifiers: Tube Guide to the Tempo Electric Model 302 Amplifier: |
|
Model 302 Amplifier : Output ![]() Original Western Electric 300B, Emission Labs 300B, RCA Globe UX-250, RCA 50 (ST-19), Sylvania 50 (ST-16 style 6A3 remanufactured as a 50)
|