2. amps-preamps
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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 j_k

j_k
234 posts
 
ARC provides a select group of 6922s that are tested for the specs to match the amp and for low noise and microphonics. I have heard a big difference in 6922s, based on where they come from.

I decided not to use ARC 6922s once in my VT-100. Never again. I will use other equivalents in NOS tubes, but if it is todays MFG tubes, go to ARC. I heard from a reputable source that ARC is rejecting 50%+ 6922s in the inspection process. I am not going to try my odds for $200 price difference for 8 tubes when a bad 6922 tube installed in a VT-100 can take out resistors and output tubes.

I am not affiliated to anyone -- just my experience and 2 cents. Kevziek -- you are not crazy, I have had the same experience.
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