These tubes have black plates and top halo getters with excellent silver getter flashing on each tube. The tubes have production codes as follows:6-13, 413, 322308, 626 and 552. Mutual Conductance test readings are as follows: 2300/2000, 1650/2150, 2150/1800, 2450/2600, 2350/2250 and 2350/2350.
Item Tag: Sylvania 6SN7GTB
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(2) Sylvania Philco 6SN7GTB Tubes Chrome Dome 3 Hole Black Plate Test Strong
Tube 1 Emissions 103% & 92% | GM 88% & 88%.
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(2) Sylvania 6SN7GTB Chrome Dome 3 Hole Black Plate Late 1950s Tests Strong
Tube 1 Emissions 91% & 95% | GM 103% & 103%. Tube 2 Emissions 87% & 112% | GM 107% & 100%.