They say only one out of 150 tubes was selected from each batch. They say the design and manufacturing of these was a covert operation only known to the German military. They say the tube specs had not been published until decades later. Be it unverified anecdote, rumor, reverent whisper from audiophiles or innocent misinformation spread by tube enthusiasts totally out of their utmost respect for the sonic wonder of the century, our picky audiophile's ears approve of Siemens CCa's superior qualities...on all accounts: matched triode sections, low noise screening, minimum 10,000-hour heater life expectancy, carefully controlled frame grid winding and anti-vibration military build - this is about as good as it can ever get in the entire 6DJ8 tubes family!
As the enhanced version of Siemens E88CC, the CCa tube naturally posses all the greatest traits of the family: the airy and transparent natural tone unrivaled even to this day, the extended yet never tizzy top end, the incisive, neutral and balanced midrange presentation, the clearly defined and deeply controlled bass that's always there with the perfect amount of weight. All these fantastic sound characteristics multiplied by three and that's what you should expect from the Siemens CCa. And the most defining sound characteristic of Siemens tubes is their ability to retrieve the deepest levels of detail in sound, and these hidden sonic layers can go a long way to reveal the subtle ambient clues that help complete building a truly 3D holographic sound reproduction. The sound stage of Siemens CCa is amazingly wide and feels like the holographic field gets "flattened" into a panoramic view of your music, still curvy and enveloping, and with added head room - nothing in the sound can escapes your ears (or eyes.) While as quiet and analytical as the Telefunken CCa/E188CC tubes, Siemens CCa's also create a warmer, smoother and sweeter German tone (and very German) that's rarely heard elsewhere.
The cherry on top for this offering: one tube bears the very special yellow mark, indicating its proud history of being a "select tube" - you get extra clarity in sound, extremely low noise (to the vanishing point) and even longer heater life.
Professional Sound Evaluation
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 (110%+ mutual conductance) on a Mercury 2000 tube tester with the following result (mutual conductance both in uMhos and in percentage of nominal):
Pair one:
Tube 1: 14,900/14,900 (119%/119%)
Tube 2: 14,300/14,300 (114%/114%)
Pair two:
Tube 1: 17,000/17,000 (136%/136%)
Tube 2: 17,000/17,200 (136%/137%)
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
Beside the world-class sound characteristics, we treasure this pair because of their pristine cosmetic condition. Nearly 100% of the paint and lettering are still clear on these 60-year old tubes. The acid etched Munich date codes are perfectly visible on both pairs:
Pair #1:
A0 1# 5C (A0 = CCa, # = Munich, 5 = 1965, C = March)
A0 1# 5F (A0 = CCa, # = Munich, 5 = 1965, F = June)
Pair #2:
#5F (# = Munich, 5 = 1965, F = June)
#5D (# = Munich, 5 = 1965, D = April)
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