tube measure numbers...?

Discussion in 'Amps and Cabs' started by Carabinerx, Apr 22, 2015.

  1. Carabinerx

    Carabinerx Member

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    Can anyone explain to me all these numbers listed on ebay gauging the life of tubes? I see Hickok, B&K, Triplett, and Tv7. I know of the whole 'no guarantee with those numbers' but something is better than nothing.

    Ive been grabbing some NOS tubes for my SFSR and they claim "98%/102%" is strong/NOS and "65/65" (min 40) is also strong/NOS.... Yesterday I won an auction for some mullard preamp tubes for cheap...and thats worrisome, but figured itd be worth it if at least one or two turned out to be good.

    Mullards on his Triplett (min 1000)
    1900/1750, 1675/1700, 1550/1725, 1500/1000....?

    [​IMG]

    What does all this really mean? I cant find a chart anywhere that gives a relative range for certain tubes on certain machines, like:

    12ax7's
    B&K: min, X; good, Y; NOS, Z
    Triplett: min, X; good, Y; NOS, Z
    Tv7: min, X; good, Y; NOS, Z

    and so on, any help here so I dont get totally boned? These tubes aint cheap, and im not rich! Thanks
     
  2. zenas

    zenas Member

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    In a nut shell it means you stick them in your SFSR and see how they sound.:)
     
  3. garret

    garret Member

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    I believe each tube has stated min/max values when new. You can test them to see how far off they are from manufactured specs.
     
  4. Carabinerx

    Carabinerx Member

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    haha, well thats the approach im employing with these tubes. Im sure they sound good, better than what I have now, but I like the idea of not having to buy tubes for quite a while. Which is what im trying to suss out of those numbers.

    Anywhere I can those factory numbers? Im not seeing anything in an initial search
     
  5. DaveKS

    DaveKS Member

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    There is no fool proof table to follow, there's so many testers with different scales out there, some simple emission testers, others mutual conductance.

    But my simple logic for dealing with it is if X = min, X is 65%, 65% is weakest tube that's still functional, so 100/65=1.5384... So I use 1.54, so on BK listed above 1000min x 1.54=1540. 1540 being 100% 12ax7 spec, if it had been less it wouldn't have made it out of factory testing back then, this is just my rough voodoo way of dealing with it. 90% is cut off point I will deal with for a used tube, so 90/65=1.384, so x 1.38 will give you 90% value, so 1380 would roughly, and I can't emphasize this enough, roughly give you 90% value on that BK.

    The one you listed that's 1500/1000, if that's true reading, one side of it is dead and it's trash bin material, should never have been sold to begin with. The one that listed as 1900 on one triode, that's over 120%, 20% higher than 12ax7 spec. There are some tubes that at times test up in 130% range, old Telefunken and Raytheon black plates ie, but their the exception rather than rule. Anyway you always need to be suspect of how well calibrated their testers are and take that as a grain of salt when looking at eBay tube sellers.

    Finding tubes that are strong is not that hard on eBay tubes, any tube functioning above say 80-85% can still sound good. But finding ones that are quiet and non-microphonic are the bane of dealing on eBay. Don't know how much you paid for that batch, if it was a to good to be true price for all 5 of those you'll usually end up with 2-3 of those 5 being a no go, eBay is a total crap shoot. If some are micro or crackly/noisy, get a partial refund if you can.
     
  6. Carabinerx

    Carabinerx Member

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    ^^
    Awesome thanks DaveKS, this the more comprehensive approach I have seen so far. If 1000 is the minimum though, wouldnt that be the 65% in this case (meaning its a bare min passable), also that the 1900 is astronomically high? I paid $58 for the set so I knew it was a risk at that price, I was just hoping to get two good ones, which may be the case, but fingers-crossed for low noise (!).

    The 1500/1000 being dead isnt a huge shock, you cant really tell in that photo, but in the others the two on the left are the questionable ones, especially the middle one thats is burnt to hell, but the right most two look clear and new.
     

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