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which is it? (or below zero VD day ramblings)

67.175.88.8

from left to right:
Sylvania 6L6GC, Rusky 6P3S, Rusky 6P3S-e and the Mesa branded Sovtek 5881/6L6 STR-425.
the Russian 6P3S plates look very similar to Sylvania 6L6 and my other American 6L6s' and nothing like a Rusky 6P3S-e

the coin bases look absolutely identical to my untrained eye

eyeballing a Tung Sol 5881 against the Sovtek pair looks nothing like the Ruskys'
I compared 4 other American branded 5881s' with the same visual conclusion they definitely ain't the same.

my puzzlement is incomplete (or fulfilled?) as I don't have an American 6550 to compare with this cast of characters

comparing data sheets, the 6L6 to me does not appear to be a 5881 or a 6550. definitely family members though. cycling the above through a UL-PP amp the Rusky 6P3S and Rusky 6P3S-e were my least favorite. A quad of Sovtek EL-34 gave the best offering versus the American 6L6s, but that's apple to oranges to me.
I was surprised to find a lot of unfavorable comments (too grainy and dark?) about the Mesa STR-425s on guitar boards where the STR-440s were preferred, but alas, I don't play a lick so I'm guessing apple to oranges again.
I know this is a totally off balance (unfair as circuit was not optimized for each of the different tubes) comparison.
Are we saying the 5881 6L6s are electrically equivalent because they don't appear to be physically and definitely not sonically?
if I only had an American 6550 to add to the confusion!
anywho.......field day time...............

"the only thing necessary for evil to succeed is for good men to do nothing"

Follow Ups:

RE: which is it? (or below zero VD day ramblings) - DAK 09:54:52 02/15/15 (2)
If you are asking if the 5881 is equivalent to a 6l6 that is correct. In spite of the differences in appearances the tubes are interchangeable. The 5881 is a heavy duty or mil-spec version of the 6l6. I am listening to a pair of Tung sol 5881s in my SE amp and the sound is very good. cheers, Dak
- RE: which is it? (or below zero VD day ramblings) - sober1 12:04:09 02/15/15 (1)
  I guess just rambling out loud about how dissimilar the physical appearances are amongst the "equivalents". And if I'm learning this tube stuff correctly, equivalent is not necessarily identical as the equivalents can have different physical constuction, different pin outs as well as different operating points?
  so to my understanding, a 5881/6L6 they are the same only different.
  
  "the only thing necessary for evil to succeed is for good men to do nothing"
  - RE: which is it? (or below zero VD day ramblings) - DAK 22:01:21 02/15/15 (0)
    The 5881 and 6l6 are interchangeable. They have the exact pin out and operating conditions. The only difference is the 5881 has a higher power output and can handle higher voltages. The term equivalent is more open ended in that the term relates more to the operating conditions. Such as the 6sn7 and 6cg7 are equivalent but obviously they are in totally different packages.
    Right now in my RH universal amp I have used 6l6, 5881, and EL37. If I switch the tube rectifier to a 5Y3 for lower voltage I can use the 6v6 tube. If my power supply was more capable (output more voltage) I would be able to use 6550 tubes. It takes tube rolling to a whole new level! cheers, Dak

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