This is a 6SN7 thread, so I think I should also post here:
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As a fellow tube addict and victim, I have to let you guys know the BIGGEST lie in 6SN7 history represented by almost ALL sellers with TV-7 series tube testers, so that hopefully no one will fall victim to these lies again!
Almost ALL tube sellers with TV-7 tube testers (be it TV-7/U, or TV-7A/U, or TV-7B/U, or TV-7D/U) will list the following statement in their 6SN7 ads, "The TV-7 minimum recommended value (65%) for each plate of the 6SN7 type tube is 50 (Gm=1250)." By the statement, you would derive that a 100% NOS 6SN7 should be measured at 50 / 0.65 = 77 on TV-7.
However, the statement is deadly wrong!!! We all know that a 100% NOS 6SN7 tube should have a mutual conductance of 2600gm. A simple calculation from the statement shows 1250 / 2600 = 48%, which does NOT agree with the 65% claimed by sellers, so the statement is obviously incorrect. I dug into the issue further in the past couple of days, and found the following chart which converts TV-7 readings to mutual conductances (we should look at the Range B column, as TV-7 uses Range B to measure 6SN7 tubes).
Using the minimum 50(1250) being only 48% of a 100% NOS 6SN7 that we calculated earlier, we can derive a 100% NOS 6SN7 should be measured at 50 / 0.48 = 104 (1250 / 0.48 = 2600gm) on TV-7. And this agrees exactly with the conversion table above (if we do a linear interpolation between 100 and 110 using the table, 104 corresponds to the 2600gm of a 100% NOS 6SN7).
So the conclusion, "A 100% NOS 2600gm 6SN7 tube should be measured at 104 on TV-7 tube testers". To get the exact percentage quality from TV-7, you just divide the TV-7 reading by 104 (or approximately minus 3 or 4). For example, a 6SN7 measured at 77 on TV-7 is 77 / 104 = 74% of NOS (or using approximation 77 - 3 = 74% of NOS). Also, "The minimum 50 (Gm=1250) on TV-7 is 48% (instead of 65%) of the 100% NOS."
To get a 100% NOS 6SN7 tube, you need to look for a TV-7 measurement of 104 or above. The 77 measurement derived from sellers' false statement will only get you a 74% mediocre tube. "The TV-7 minimum recommended value (65%) for each plate of the 6SN7 type tube is 50 (Gm=1250)." hence 77 is the 100% NOS reading derived from the statement, is the BIGGEST lie in 6SN7 history. Almost ALL tube sellers with TV-7 series testers list this false statement in their 6SN7 ads. I think we should remind or report the sellers when we see the false statement again. In the past couple of years I used to think 77 from TV-7 is a 100% NOS 6SN7 tube, but now I know it's merely a su*king 74% mediocre tube. And I paid a premium for quite some mediocre 6SN7 tubes because of the lies made by sellers with TV-7. Hopefully no one will fall victim again after reading what I wrote above.
Caveat Emptor - Buyers Beware!
Was it something I said?
I know a lot of people and one friend had been asking me if I had extras but mine disappear pretty quickly in amps I build for friends, and I have been known to run four in a Freya +. I own 1578's covering three decades but only but the 63's when I can find them. The others have more pronounced midrange but I am not quite as happy with the highs. The 63 is more balanced over all yet the mids are still wonderful.
I'm sorry you had to go through something like that, lot of tension with everything that's going on in the world. He might have shipped that tube after all. Some dealers are really busy sometimes and should answer you promptly if they can. If he did send you the tube just take it and don't deal with him anymore. Not worth the squeeze to prove a point sometimes. Good luck with that tube, and keep us posted.
He did not send tube but refused to return the money either.
Sometimes you can win by losing.
I can tolerate late shipping and response but not racial slur.
With the world trying to educate and elevate itself, this guy must be living under a rock to make a remark about ethnicity as if somehow that is relevant. I am truly sorry you had to endure a racial slur.
