6SN7GT / G:

This is the original version of this tube. It may be found in all three sizes of glass envelope. The Sylvania Tall Boy types have two triangular shaped plates facing each other mounted high in the tube, with either a top or bottom getter. The early Sylvania types had a top getter and silver flashed the entire top of the tube, sometimes called "chrome tops". Many brands used this design, but the high mounted triangular plates means it most likely was made by Sylvania. The early RCA "GT" types were usually in either a medium or short envelope and have a grey RF shield sprayed on inside the glass. The GE and KenRad types were similar, but the inner glass coating is deep black. These tubes usually have flat black plates, like large 12AX7 blackplates. The military versions of these are the VT-231 and are in very high demand today.

6SN7GTA / GTB:

This is the later improved version, and the improvements were primarily geared toward the TV chassis designers who demanded more max. plate wattage and voltage, where vertical circuits can put up to 1500 volt pulses at 7 watts on the plates. For hi-fi audio use, these improvements are meaningless. These are fine tubes, nonetheless. Most are found in the short glass envelope, but some brands like Raytheon used the Tall Boy style. Sylvania made tubes have the triangular plates mounted lower, and set at angles to each other, although some of the very earliest examples of the GTA types still used the dull blackplates facing each other. RCA used the flat black plates "sideways" to each other, and GE used the grey plates parallel to each other. The Sylvania types in demand have a large top getter patch. The earliest Sylvania GTA types have a green label and heavy top getter flashing extending down the sides of the tube. The early GTB types are similar, but have a yellow or red label. The versions from the 1960s have the getter just covering the top of the tube. All of these have the same black triangular plates and are excellent tubes. The GE types have a side getter and large parallel grey plates, and the RCA used both bottom or side getter. Most other vintage USA brands you find will have been made by these three vendors, and will be one of the above variations, regardless of brand on the label. A few were made with brown micanol bases, the RCA types being very dark brown, the GE types being a lighter, marbled brown. Many audiophiles prefer either the Sylvania chrome tops, the RCA, or the GE side getter over any others, even over the military or redbase types. These are all a great bargain now, and are sure to be rare and expensive tomorrow.

6SN7W / WGT / WGTA:

This type indicates a military spec tube that was not made for consumer use. These usually have extra support posts on the plate structure, heavy mica spacers, and brown micanol bases. These also have the famous triangular shaped black plates. They have been ruggedized to withstand shock, the brown low loss micanol base resists mold, mildew, and fungus growth, and they can withstand heat even if used upside down. The early Sylvania 6SN7W types from the 1940s had a metal collar around the base, then later a black base. These look internally alot like the early Sylvania GTA types listed above. Sylvania made these for other brands as well, including RCA. Easy to spot as they have the triangular blackplates facing each other in a short bottle, with a very heavy chrome top flashing extending down the sides of the tube. These are RARE and worth seeking out! The WGT and WGTA types all had brown bases. Only the WGTA types made in the late 70s and 80s reverted back to black bases then coin or wafer bases. These are all wonderful tubes, are long lived, and sound fantastic. No wonder they are fast disappearing from the vintage market.

5692: