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Philips Miniwatt SQ E88CC = 6922 Matched Pair - Heerlen, NL 1966/67 - NOS

Philips Miniwatt SQ E88CC = 6922 Matched Pair - Heerlen, NL 1966/67 - NOS

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Soundlumia's Opinion

The beauty, the legend, the classic, the Special Quality(SQ) - this is the super tube from Heerlen's high echelon that doesn't break the bank. Known for their superb musicality and ultra low noise, thanks to Philips' proprietary SQ design, these tubes remain among audiophiles' top choices for critical listening. 

Immediately appealing is the super smooth highs offered by these tubes with lots of open air. The overall tonality of SQ is warm, musical and euphonic. The midrange displays some secondary octave nuances, which is very unique and can hardly be found even among the top-end German tubes. Similar to the Telefunken tubes, the SQ's can create infinite levels of harmonic depth and a liquid sonic texture without altering the musicality of the sound. The bass on these is the clear winner of the Heerlen tubes family: articulate, accurate, deep, textured, full-bodied and powerful. The sound stage is wide and structured - it feels the dimensions of the sound shape are clearly defined no matter how it moves.


Vocal representation on the SQ's is close to Mitcham and Blackburn Mullard tubes in terms of warmth, sweetness and texture, making them great alternatives to Mullard's as the best vocals tube. But what truly shines on SQ tubes, especially the ones from the 1960s like this pair, is their magic in portraying piano music: creamy smooth, richly colored, realistic and intimate. For many audiophiles (incl. ourselves), they're the go-to tube for piano sound. Listening to Claudio Arrau's Beethoven Complete Piano Sonatas on these tubes should be on your bucket list if you happen to be into classical piano music, but even if you are not, these tubes' superb "interpretation" of piano music from any genre will amaze you.

The ultra low noise on SQ's also sets them apart from most of the high-end tubes. They don't just compete with Telefunken tubes in low noise; they're known for being a long-term leader in low noise. As a result, you get superb detail and clarity from these tubes as well.

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 set was tested and certified by RoeTest V11 Professional Tube Testing System with the following result: 

Tube 1:

Measured transconductance(GM): 12.91/12.7 mA/V  - 103%/102% (100% = 12.50 mA/V)
Measured plate current(IA): 15.599/14.939 mA  - 104%/100% (100% = 15 mA)

Tube 2:

Measured transconductance(GM): 11.89/12.46 mA/V  - 95%/100% (100% = 12.50 mA/V)
Measured plate current(IA): 13.851/14.849 mA  - 92%/99% (100% = 15 mA)

NO shorts, leakage or gas. NO noise or microphonics.

Curve trace is also included in the original RoeTest report.

Appearance & cosmetic condition

Silkscreen: 95% - 100% (Pristine)

Date codes: 

7LD ⊿6E2 (⊿ = Heerlen, NL, 6 = 1966, E = May, 2 = Week #2 of the production month)
7LD ⊿7J5 (⊿ = Heerlen, NL, 7 = 1967, J = October, 5 = Week #5 of the production month)
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