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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
swampwalker's avatar
swampwalker
5,138 posts
 
Kev- I have been told that Sovtek is just a generic term chosen for export to the West and that there were (are?) many different manufacturers. If that is true, take that and add that to the other variables, and what you report is not at all surprising.
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.
fletchj
91 posts
 
Welcome to the world of tubes. A manufacturer makes tubes, to pass electrical tests. A vender, such as Ram, New Sensor, Audio Research, etc., tests tubes, to meet certain electrical parameters. Certain venders, burn in tubes, so that the ones, that will fail early, will fail in burnin and will not wind up, in someones gear. Then they are tested again, and graded. 99% of the time, the customer, is the first to actually listen to music, through the tube. No manufacturer today, comes anywhere near, the consistency of manufacture, that companies had, during the tube making heyday. Different runs, off the same line, on the same day, will sound different. Every tube maker today, makes a great sounding tube. Its just that they have problems, consistently making a great sounding tube. No manufacturer, is going to destroy tubes that test great, just because they don't sound great. A tube that tests perfect, does not neccessarily, have to sound perfect.
brf
1,715 posts
 
Did you try putting the 6922 from your SF into your ARC amp, and did the sound of your ARC change? I'm curious as the ARC's sensitivity to a change in input tubes.
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.
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