12x7 tubes

NOS Telefunkens sound best, but are pricy. Try anything else to get your amp "on the air."

Tung sol gold pins are often recommended as a good upgrade for that component. I got rid of my black ice dac, had terrible hum issues....I got a border patrol dac, could not be happier.

Stellar Quality

Space and military applications required electronics that could operate reliably in extreme environments of high altitude, high acceleration/vibration and even space, where high levels of radiation are present. Incidentally, one of the reasons Russia continued to manufacture tubes was because these thermionic devices are immune to an electromagnetic pulse (EMP), the gamma ray burst that an atomic bomb releases upon exploding—Russian MIG jet fighters were equipped with tube circuitry in their radar systems so that an EMP would not interfere with onboard navigation systems.

Tube reliability was a real and ongoing concern for the US military. You may have seen the initials ‘JAN’ stamped on Philips N.O.S. tubes, which is an acronym for ‘Joint Army Navy’. These are ruggedised tubes manufactured for the military. During world War II the American military initiated a ‘ruggedisation’ program with aim of improving tube reliability in the field. For example, there was concern that delicate electronic comms equipment thrown around in the back of a jeep hurtling along a rock strewn dirt track might not fare too well. To remedy this perceived problem with reliability tubes were designed with shorter, stockier anodes, additional or thicker support micas and a very complex and elaborate tube numbering system evolved along with the numerous revisions of tubes [Getting the Most Out of Vacuum Tubes by Robert B. Tomer pages 72-75]. Reliability of electronics and tubes in military and space applications was of paramount importance.

True some tubes were designed from the ground up for military application, but most were not and were simply tested for shock and vibration by the factory for the military. The internals of these tubes were no different than the tubes released to the civilian market. Further, in most cases, audio considerations didnt exist for military applications, perhaps in some cases noise could be an issue but even this may be a stretch. Now if certain military design concerns necessitated change that influenced the overall tube market back in the day I cant comment to this. To assume that a JAN tube or more importantly a JAN designation indicates a better sounding tube would be a mistake.