The 6SL7WGT is the military version and usually will have more support than the commercial version. More support usually equals less microphonic problems. Some of them also had brown bases which are probably repackaged military 6SL7WGT's. Any of hese will certainly outlast and sound far better than ANY of the shit produced today. Like all of the other brands mentioned, these also vary somewhat in appearance and construction depending upon when they were made.
Early ones have black cylindrical plates and bottom getters.
The glass is clear. Later production units had the same plate structure but the getter was moved up to the top. Earlier versions made in the 50's, 60's had brown bases and nice thick mica wafers for extra support and superior microphonic elimination. The plate structure is shorter and heavier than the standard version. Later units made under the Phillips ECG during the 80's look exactly the same except for a black colored full base.