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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 5 responses by kevziek

kevziek OP
323 posts
 
I did make a slight error. The Sovteks in the VT100 are not of the same year as the other sets. The other sets are stamped 98-12 & 99-01. The VT100 tubes have no date, but the lettering and internal construction are identical. They are AR sourced, in since amp was manufactured (1997). So, my feeling is that either they are so critically measured & chosen, that they sound better. Or, the manufacture of the tubes varies that much.

I have some older (1996) Sovtek's where the construction looks different. Plus some unmarked ones that I think originated from Kevin Deal. I'll try these and let you know my results.

The amp was made in 1997
kevziek OP
323 posts
 
Swampwalker, Sovtek is a brand made for New Sensor Corporation of USA. The owner was in business twice. He came into bad times in the mid 1980's, closed shop, then he started New Sensor several years later. The tubes are made in Russia by, I believe, Reflektor Factory, a large tube manufacturer. I don't believe they were always made there, especially back in the 80's. Someone correct me if I'm wrong.

Back to my tubes, all the 6922's I compared were made by the same factory and are the same design. If you look at them all, they are identical. That's the part that boggles my mind.
kevziek OP
323 posts
 
The VT100 has very complicated adjustments for the 6922's, so placing other 6922's in it is not the best idea. I'm afraid of blowing a resistor. My guess is that if the adjustments are so critical, just throwing some other tubes in there will result in worse sonics.
kevziek OP
323 posts
 
Any other Power 2 owners who experimented with 6922s out there?
kevziek OP
323 posts
 
Meby, I'm still sorting out the two amps sonics. The ARC has more definition in the high end, but sounds a little lighter overall. Power 2 a little fuller, voices sound weightier, but some of the clarity is gone. Both sound good, but neither is perfect.
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