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HP Select Amperex 6DJ8 ECC88 Preamps Tubes Matched Pair - Holland 1965 - NOS

HP Select Amperex 6DJ8 ECC88 Preamps Tubes Matched Pair - Holland 1965 - NOS

Regular price $117.80 USD
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Perfectly matched & balanced pair of vintage HP Select Amperex 6DJ8(ECC88) audio tubes - Heerlen sound from 1965 - Super Strong NOS - Very Rare

Product Summary

These are the legendary "medical tubes" made by Amperex Holland for Hewlett-Packard's medical devices distributed around the world. Each tube had to go through rigorous test and selection processes designed, implemented and monitored by HP. What you get is the best from the best candidates in build quality and low noise. Manufactured and released only in limited quantity, these tubes are elusive to find and remain top choices of critical listeners and tube enthusiasts. 

Sound Qualities

Despite the HP label, you get the "textbook" Amperex Holland midrange presentation that is transparent, natural and expansive, with a slight touch of warmth that illuminates your musical world. The top end is super airy, smooth and nicely extended like one would expect from the best Siemens tubes. Vocals are intimate, sweet and forward (but not right in your face) and that always reminds me how the vocals sound on the best Mullard tubes. Bass is deep and well controlled and the accuracy feels very similar to the high end German ECC88's (Siemens, Telefunken.)

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 

This pair tested Super Strong NOS (120%+ nominal mutual conductance) on a Mercury 2000 tube tester with the following result (mutual conductance in uMhos):

Tube 1: 14,800/15,100 
Tube 2: 14,000/14,800

Good tubes start around 7000 and new tubes (incl. NOS/NIB) 12,500 - 13,000, and 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 would mean to your sound experience, it's actually quite straightforward: mutual conductance directly translates to tube's ability to amplify sound so the higher the numbers the stronger. 

Appearance & cosmetic condition

We treasure this pair also because of the great cosmetic condition of both tubes - over 90% of the paint is intact and well preserved. The practically identical Heerlen factory date codes etched on glass are perfectly visible on both tubes: 

delta 5H2 (delta = Heerlen, 5 = 1965, H = August, 2 = 2nd week of the month) 
delta 5H3 (delta = Heerlen, 5 = 1965, H = August, 3 = 3rd week of the month) 
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