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I'm Freaked Out by this Tube comparison

I was comparing two amplifiers - ARC VT100 Mk II & SF Power 2. They both have Sovtek 6922's in the input stage that were manufacturer selected and matched of about the same vintage. Both have 8 new EH 6550's, matched & measured.

On cymbals, brushes etc, the Power 2 had a more distant and smaller presentation that lacked detail. Chesky guitar recordings sounded thinner, had less ring, less body, less resonance. Overall, less involving sound.

I attributed the sonics to the design of the amplifiers. I had a third set of Sovtek 6922's that I put in the Power 2. No noticeable difference.

THEN ------ I decided to take the 6922's out of the VT100 & put them in the Power 2. I couldn't believe my ears -- now the Power 2 took on much, though not all, of the character of the VT100. The cymbals, etc. became more detailed, more present, more resonant. So did the Chesky guitars, and now with more body and resonance. More decay. In some respects, the Power 2 sounds better than the VT100.

Am I crazy??? I can't believe that one set of the Sovteks could be that much better than the other. Or is Audio Research's claimed intensive selection process responsible?

There is no biasing for the 6922's in the Power 2. SF told me to replace tubes, you just plug and play. The output tubes (6550s) were accurately biased in both amps.

What gives here?
kevziek

Showing 1 response by clueless

clueless
763 posts
 
Interesting story Kevziek. I do not think your nuts but stick around tubes long enough and you will be (Just kidding).

I am not a 6922 user at this time so I am a little out of the loop but I've heard there are a handful (up to 8 or 9?)different Sovtek 6922s that are not always easy to identify. Lots of mislabeling and lazy matching going on too. Maybe they are not as close to same vintage as you were told? Maybe you had a mismatch or a poor tube. I guess that's why places like vintagetubeservice.com/page4.html and tubeman.com , vacuumtubevalley, spend so much time testing pairs and matching. It's almost impossible to know based on what you said. There is a reported very basic difference between old and new Sovtek 6922s but I guess that doesn't surprise either of us.

It's hard to believe that "identical" tubes can sound different but it may be a little like speaker drivers. I have a little more experience measuring that stuff. They might all come out of the same factory but are all a little different when you measure them and the mfg's specs can almost never be depended on and then they take on a life of their own when you make them part of a specific circuit and enclosure. If you want a nice sounding pair you have to hand match and it's not hard to make a mistake.

Thanks for the story

I remain,
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