Since I make no claims to be a tube guru I started trying to go through a plethora of emails I filed away from the 6SN7 guru who bestowed that cache of vintage 6SN7s (and some 6922s) upon me. I thought I remembered him telling me that the tubes that the military had contracted out for were made to better withstand vibration as many of them were going to be used in different avionic applications.
Anyway, I have a crapload of emails on those tubes and I wasn’t finding the one I was looking for, but I’ll paste a blurb from one of the first ones I found:
The W in WGTA is the designation for "ruggedized" construction. Thicker mica supports, extra support rods, smaller bottle ... all supposed to reduce the effect of physical shock/vibrations.
That was referring to a pair of 1974 Sylvania 6SN7 WGTAs that I don’t think were made for military applications as I think that (at least our) military must have been done with vacuum tubes by then.But another pair of 6sn7s he bestowed upon me when he was cleaning out his cache of tubes he no longer used, and these really are jewels, were two ’52 Sylvania "Bad Boys" and I have to think that these were military as he sent them to me in their original packing box (not tube boxes, but a heavy duty box) with a faded placard labeled "SPARE PARTS" , and also states that the contracter was "PHILCO CORP." and "MFG BY [a faded "Sylvania is typed in] "DATE INSPECTED" [9-19-52" is typed in, faded but still legible] under that "PACKED FOR OVERSEAS SHIPMENT" and in the bottom right hand of the placrad is a little picture of an anchor with "ORD" in the middle of the anchor and "U.S.. NAVY" at the bottom.
So I assume that these were made by Sylvania for the Navy, and these are tied for first place as my absolute favorite 6SN7 sonic presentation so far.
My two runner ups were a pair of black glass RCA VT 231s and a pair of Tung Soll VT231s ("probably NLT 1947"). I think maybe the reason that military tubes have the favorable reputation that they do is because a large percentage of the tubes that were made way back then were made for the military and therefore a lot of the vintage tubes that are being sold today may have been made with a military contract in mind so when we find one we really like, it’s not unusual for it to be "military surplus" of sorts.