[Xcalibur255]

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Is there a sound difference between VT-231 and no VT-231 tubes ?

At least 2/3 of the time the VT-231 and 6SN7GT branded tubes from the same manufacturer in the same time period are the exact same tube.  VT-231s often went through an additional round of testing to meet military criteria, but physically they were the same tubes.  There are exceptions though.  A good example would be Raytheon and Sylvania tubes which have extra support rods in their VT-231 and W versions respectively.

 

[rosgr63]

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Have you got photos to share?
 

Here is the getter detail
 

 

[Oskari]

Thanks! What is it that you find strange in that?

 

[rosgr63]

The way the bracket is welded onto the D frame and the way is bent down.
The photo cannot give the true perspective.
 
The D frame is common otherwise.

 

[Justin Uthadude]

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It appears that an old 3 cell car battery produced about 6.3V (2.1V X 3) and I have found an old tube used in Ford Motor Co. radios that needed 6.3V for the heater. It’s almost totally chromed. Anyone recognize this?
 

 
Hint: it’s from our friends at 312. The funny thing is that the back says to only replace with a genuine Ford tube!
(Sounds fabulous in my headphone amp)

 

[Audio-Omega]

Have you checked ?
 
 
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May have a pair. Let's open up the wooden box for a late look and listen, shall we? Of course, I couldn't afford the VT-231 version. But will check anyway...
 

 

 

[Anaxilus]

Quote:

At least 2/3 of the time the VT-231 and 6SN7GT branded tubes from the same manufacturer in the same time period are the exact same tube.  VT-231s often went through an additional round of testing to meet military criteria, but physically they were the same tubes.  There are exceptions though.  A good example would be Raytheon and Sylvania tubes which have extra support rods in their VT-231 and W versions respectively.

This.  Military designations aren't necessarily a guarantee of improved durability or SQ.  Some claim certain more durable designations actually sound worse depending on the tube.  The process was also rather random w/ one out of ten (or some other ratio) samples being tested and then the whole batch being certified as mil spec.  So there are nuances to be aware of.
 

 

[Xcalibur255]

Quote:

.
It appears that an old 3 cell car battery produced about 6.3V (2.1V X 3) and I have found an old tube used in Ford Motor Co. radios that needed 6.3V for the heater. It’s almost totally chromed. Anyone recognize this?
 

 
Hint: it’s from our friends at 312. The funny thing is that the back says to only replace with a genuine Ford tube!
(Sounds fabulous in my headphone amp)

My second favorite 6SN7 of all time, right behind the the BGRP Tung Sol and the tube I use most in my current amp.  Though, mine all have the shorty plastic base, which I thought was how this particular variation came.  I have only ever seen them with date codes ranging from 1951 to 1953 myself, the same time period as the "bad boy" but definitely not the same tube despite having the same type of plates.
 

 

[Justin Uthadude]

This tube has a date code of 852, which I figured meant the end of 1948 or 1958. I can find no tube resembling this that Sylvania made in 1958, so maybe this is from 1948?

 

[dminches]

Quote:

This.  Military designations aren't necessarily a guarantee of improved durability or SQ.  Some claim certain more durable designations actually sound worse depending on the tube.  The process was also rather random w/ one out of ten (or some other ratio) samples being tested and then the whole batch being certified as mil spec.  So there are nuances to be aware of.
 

 
The process is far from random.  There are real statistical approaches to sampling which define the number of samples you need to test to insure a positive result as a certain probability level.  The government may not be the most efficient organization but the military does understand sampling, testing and tolerances.
 
Having said all that, they didn't build the tubes to maximize sonic properties.
 

 

[Skylab]

Right, but the military was HUGELY interested in reliability and longevity.

 

[rosgr63]

David & Rob would you agree that the best US made tubes stayed in the US?
 

 

[Skylab]

I think the majority of them probably have, yes, although in the last 15 -ish years of the Internet era many more have left the US that probably ever had prior.
 
Clearly though there were some large stocks at US Military bases overseas that did make it out into the civilian population as they were disposed of.  
 
And of course, Western Europe and the UK made some of the finest tubes around, so there was likely not that strong a demand for US made tubes.  There were many outstanding tubes made in both the US and Europe.  I am guessing that many more total tubes were made in the US, but I don't know that for sure.

 

[Xcalibur255]

Quote:

This tube has a date code of 852, which I figured meant the end of 1948 or 1958. I can find no tube resembling this that Sylvania made in 1958, so maybe this is from 1948?

It would have to be 1948 I would think.  By 1953/1954 Sylvania was transitioning to their off set angle triangular plates you see the GTA and GTB tubes pretty much from that point on.  I think some of the military labeled W tubes were still using the parallel plates until the later 50's, but the actual plate type was different even though it looked almost identical.  Assuming we're right (and I'm assuming its the same tube as the one I have, minus the different plastic base) what you have is closely related to what you find inside a metal base W tube, and IMO one of the true treasures of the 6SN7 world.  In my personal opinion they outperform the "bad boy" and by a considerable margin too.  It's the only tube I've personally heard that I consider on the same footing with the BGRP Tung Sol for resolution.  Some of the tubes I often have seen cited as peers to that tube, like the VT-231 Raytheon, are indeed great tubes but still not in the same class to my humble ears.

 

[rosgr63]

Skylab I agree 100%.
There were some fine tubes made both in the US and Europe.
Could you please redefine your favorite 5 6SN7's?
 
Xcalibur are you referring to the 6SN7W black base?
Can you also let us know your favorite 5 6SN7's please?
 
I would like to invite all thread readers to contribute their top 5 6SN7's.
It will be interesting to see what different people like.
They don't have to be expensive or rare tubes but what you like best.
Thanks.