• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

History of Sylvania 6sn7/6sl7?

M

Musictubes

Isaac
Does anyone have a good timeline for the different types of 6sn7 and 6sl7 that Sylvania made? Common wisdom is that the loctal versions of 7n7 and 7f7 plus the 12v 14n7 and 14f7 mirrored the production of the 6sn7 and 6sl7. That mostly seems true but I have noticed some exceptions.

I have a few 7f7 that are built differently than any other 6sl7 that I can find. It has the copper support rod like the metal base 6sl7wgt but is black plate instead of grey and has slightly different micas. The metal base 6sl7wgt is the only 6sl7 Sylvania made with a copper support rod. The same holds true for the metal base 6sn7wgt, I'll get to that one in a sec.

Image (1).jpegIMG_0748.jpeg

I have also seen the same construction in 14f7 and 12sl7 but not any of the 6sl7. Most do not have the copper support rod, or any support rod for that matter. I'm trying to figure out what the overlap was between these loctals (and 12sl7) and the elusive metal base W version. My first thought is it was just a timing issue. They had the tooling set up for the W and then decided to make a run of the loctals. Does anyone have a good idea of when the metal base 6sn7 and 6sl7 were made? Loctals never seem to have any date codes but these particular 7f7 have the old leaf logo on them. Plus, the boxes say they were made for the US Army Signal Corps by Hygrade Sylvania. Doing a bit of research it looks like they stopped using that branding by 1946. What is the oldest Sylvania made 6sl7 or 6sn7? I keep seeing the "fact" that Loctals were only made for a short time but that doesn't seem true since you can find newer versions of the 6sn7 in 7n7.

I got onto this search because I noticed the 14n7 is the only *sn7 with a copper support rod other than the unobtanium metal base 6sn7wgt. I have every other version of the *sn7 including the 7n7 with (non copper) support rod and even the elusive National Union round plate 7n7. The 14n7 is clearly better in my system. I don't have every variation of the Sylvania but I have a few and these 7f7 with support rod are also the best sounding to me.

Anyone have a timeline for the production of these or have a good theory as to why they have that copper support rod?
 
Register to hide this ad
Mr Boochie said:
https://www.worldradiohistory.com/A...m-Tube-Valley/Vacuum-Tube-Valley-Issue-11.pdf

Pages 3 - 9. :)
____________

I use Ludwell Sibley's "Tube Lore II" as my type and sub-type reference.

https://www.tubesandmore.com/products/tube-lore-ii-reference-users-and-collectors-2nd-edition
Click to expand...
Thank you so much! That does help. I never read VTV, I was more about Glass Audio:). I do think the ranking they gave the 6sn7 tubes has had a long shadow. I’m positive that a lot of the chatter on Usenet back in the day was by the the same folks and I heard their opinions quite often.

It gives 1942 as the first year of Sylvania 6sn7w production. That puts some info into context. If my 7f7 were made in 1942 it would make sense for the box to say Hygrade Sylvania. I do wish they had more dates for the other tubes. They just say 1940s. Since the bottom getter 6sn7 was also made with JAN designations in the 1940s I assume the copper post era only lasted a few years.
 
Eric Barbour (VTV) is an excellent author of tubes (the history and function). He helped to steer the resurgence of the Svetlana tube manufacturing (St Peterburg) in the 1990s-2000s.

A blurb by Jim McShane, including Eric Barbour, when he was with Svetlana.

________________________

Let me clarify a couple of things and see where that leads us.

First, I find enough difference in performance between the Svet/SED 6550C and KT-88 that I carry the 6550C but do NOT carry the KT-88. The 6550C is not as rolled off on top as the KT-88, and coupled with an excellent sale price, I believe the tube is a good value. It is NOT the ultimate tube in the family, as my "ranking" post tried to show—at least IMHO.

Second, the 6550 Svetlana/SED tubes have undergone several production changes over the years. They initially suffered from red spots on the plate (as do the current production Ei KT-90), and several changes were made to improve that situation. According to Eric Barbour, the square holes in the tubes were designed to allow the use of a screen alignment fixture in production. The screen alignment situation was remedied, and the red plate problem was fixed.

There were earlier tubes with round holes in the plate—I have one—but those have long since been discontinued.

Let me be clear: whatever the construction/engineering reason, I feel the SED 6550C is a far better tube than their KT-88. I carry the 6550C, but I don't carry the KT-88.

Jim McShane, July 13, 2004.
 
Last edited:
index.php

isaacc7@cox. said:
Does anyone have a good timeline for the different types of 6sn7 and 6sl7 that Sylvania made? Common wisdom is that the loctal versions of 7n7 and 7f7 plus the 12v 14n7 and 14f7 mirrored the production of the 6sn7 and 6sl7. That mostly seems true but I have noticed some exceptions.

I have a few 7f7 that are built differently than any other 6sl7 that I can find. It has the copper support rod like the metal base 6sl7wgt but is black plate instead of grey and has slightly different micas. The metal base 6sl7wgt is the only 6sl7 Sylvania made with a copper support rod. The same holds true for the metal base 6sn7wgt, I'll get to that one in a sec.
Click to expand...
Have you ever heard of the round-plate TungSol (USA) 6SN7GT?

Tungsol 6SN7GT round plates - 1942.jpg

tungsol 6SN7 VT231 round plates.jpg
 
You must log in or register to reply here.
Back
Top Bottom