Tube Summary
These are the legendary "medical tubes" made by Amperex for Hewlett-Packard's medical devices distributed around the world. Each tube had to go through rigorous testing and selection processes designed, implemented and monitored by HP. What you get is the best from the best Amperex tubes in build quality, life span and ultra low noise.
Among the greatest Amperex tubes ever made, the USA 6922 D-getter version is undoubtedly one of the most sought after by serious audiophiles. They are as sweet and airy as the Amperex Holland 6922's, with even better detail and very spacious sound stage, and the tone is smooth and absolutely grainless. Bass is deep and accurate but nevertheless well controlled and doesn't feel too punchy. Vocals on these tubes are a slightly more forward than their Holland counterparts and they sound very warm and intimate, as a result of thicker presentation in the upper midrange, which is uniquely found in the Amperex USA 6922 production.
The pair worked wonderfully and sounded terrific in our professional studio setup for monitoring.
- Input: Cambridge Audio CXC V2 dedicated CD transport + Schiit Audio Bifrost 2 Multibit DAC
- Amplification: Liquid Platinum Tube Amplifier by Alex Cavalli
- Output: Focal Clear MG Pro open-back headphones
Our full tube sound review was written 100% based on the actual listening experience while this pair of tubes were running in the system described above.
Professional Tube Testing
Both tubes tested Strong NOS on a Mercury 2000 tube tester with the following result (mutual conductance in uMhos):
Tube 1: 13,600/13,800
Tube 2: 13,700/13,200
Good tubes start at 7000 and new tubes (incl. NOS/NIB) 12,500 - 13,000, and the Mercury 2000's rated mutual conductance (nominal) for new tubes is 12,500. Test result can also be seen in the pictures. In case you wonder what all these numbers mean to your sound experience, it's actually quite straightforward: mutual conductance directly translates to a tube's ability to amplify sound, so the higher the numbers the stronger.
Appearance & cosmetic condition
We treasure this pair also because of the pristine condition of both tubes - 100% of the paint is still intact and the identical date code etched on glass is perfectly visible on both tubes: 7L5 *0J (7L5 = change code, * = Amperex New York factory, 0 = 1960, J = October).
