Hi All,
Here is a review of the Sylvania 6CS6 (EH90) tube after appr 60 hours of burn in. (Once I was in a shoe store Midwest and saw a sign that said: "Near Pair". Apparently, somebody had sold someone 2 different sizes, and what was left was a 7 and a 71/2; thus "near pair." )
The Sylvanias are both 6CS6, but the etching of the designation is a little bit different on the two tubes. Likewise, the boxes are slightly different in color. The tubes otherwise look the same, and sound the same. My assumption is that they can be viewed as a pair, but from two different production runs. Take a look:
It was a challenge to find a pair at a good price, but ended up paying less than $6 for the pair, including shipping. Was not able to decipher the dates, but it is safe to say that the tubes are from the 50's-60's.
In my 18 months odyssey to find the perfect 6AK5 tube I learned a lot of things. My conclusion about "house sound" is that there are "house traits" instead. The Sylvanias stood out as the sound stage champions. These 6CS6 tubes have the widest sound stage I've heard so far.
I have a recording with a clarinet and banjo solo. Most tubes place the banjo on the right, and the clarinet in the middle, which makes this very nice recording annoying to listen to. It's like half a sound stage. These tubes place the banjo outside the speakers on the right, and the clarinet all the way to the left. Amazing.
Now for listening impressions: EF95 1/7 and 2/7 - nothing special; mid range OK, lacking in rhythm and pace.
EF 92 (done on EF95 6/7 setting): Quite good bass, mid range, rhythm and pace, but too skewed towards the treble; too sibilant on many recordings.
EF95 NS (no strap-plug and play): This is it! Viva la Heptode! Excitement, musicality, good rhythm, pace and timbre. Very good bass with excellent slam and attack, but not the deepest bass.Brings out the essence of the music without excessive analytical detail. Superb instrument separation and imaging. Mid range very good, treble detailed.
Cons: The tubes are very sensitive to the recording quality, and you immediately hear the differences in the recording venue. There is a peculiar and curios ability to overdose on the treble on certain bright recordings, making them unpleasant to listen to. Can't figure out what level of treble or type of recording triggers this response.
Summary: Not the ultimate in bass and treble presentation, but very pleasant, warm, musical tubes with a full bodied sound with an enormous sound stage. Recommended.