Brit01 said:
All 6SN7 use the GT style envelope so that is basically a meaningless distinction. There are however GTA and GTB which are improved types. GTB types have significantly higher plate voltage ratings and slightly higher plate dissipation ratings than GT or GTA.
I've probably missed something along the way.. Read data sheets for the old types.
Incidentally I strongly recommend the Sylvania 6SN7 which comes in all 3 flavors depending on vintage.. Available very reasonably on eBay.
Brimar gets another strong recommendation, but unless you luck into some locally at a junk shop or similar these are liable to be very pricey.
Most coin base 6SN7 (mostly late GE) aren't worth worth the trouble.
Finally if you must have new production both the EH and Tungsol reissues get good reviews, they are made by New Sensor (Sovtek) at their Expo Pul plant. (Formerly Reflektor)
Oddly enough someone in China is building 6SN7 in globe style envelopes, I've not seen or heard any of these - and since they are rather expensive I would pass.
The only real distinction between 6SN7s and 6SN7GTA/Bs is that the latter was "hardened" for vertical deflection duty. The Pd= 5.0W (up from 3.5W) and the control grid had added radiator wings for operation at Vgk positive. For audio useage, that probably doesn't make much difference. The Sovtek 6SN7s look like 6SN7GTA/Bs. Been using these as cathode follower grid drivers, and they work great.
Miles Prower said:
I should have figured that this would not be one of my better days..
Upon reading some of these later posts I thought I must have been hallucinating when I originally posted, and unfortunately I was not completely accurate in my previous remarks about the plate dissipation and voltage ratings between the various types. I didn't get the story quite straight, but actually there is a difference between the earlier GTs and the later GTA/GTB.. The original GT had a plate voltage rating of 300V max and a max plate dissipation rating per plate of 3.5W.. See here for an earlier Sylvania data sheet that shows this to be the case:
http://www.mif.pg.gda.pl/homepages/frank/sheets/137/6/6SN7GT.pdf
The GTA apparently had the upgraded plate ratings, and the GTB added a controlled warm up characteristic for series heater strings.
Later data sheets all show the specifications for the GTA/GTB and I have older data books that agree with the Sylvania data sheet cited above as well.
The GTB will sub for any of the other 6SN7 types without issue, older GT types will not stand up well in circuits that were designed to run the GTB hard. (I have had this problem in my own designs.)
This will particularly be the case with rare and expensive war (WW2) and early post war vintage 6SN7. (Don't ask me how I know this
)
As I understand the original nomenclature, if there was no postscript it was a metal-bodied tube, a postscript of 'G' meant a glass envelope (with an old-fashioned 'coke-bottle' shape) and 'GT' meant a glass tubular envelope (cylindrical).
There was, for instance, a 6V6 (metal), 6V6G (glass) and 6V6GT (glass tubularr).
The 6SN7 appeared only in glass tubular guise, so the 'GT' postscript was often omitted since it served no purpose.
There was, for instance, a 6V6 (metal), 6V6G (glass) and 6V6GT (glass tubularr).
The 6SN7 appeared only in glass tubular guise, so the 'GT' postscript was often omitted since it served no purpose.
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