10-15-2013, 07:17 AM
The way I understand it, Sylvania originally designed and marketed the Loktal tubes for mobile applications like car and aircraft radios. They rated the heater voltages at the nominal voltage of lead acid batteries under charge, 7 and 14 volts. If you look at early Sylvania tube manuals, the heaters are rated at 7.0 V and .32A or 14 V and .16 A
Of course it was also a way to differentiate this new line of tubes from the competition, so there was probably some marketing considerations involved.
In later manuals, Sylvania just rated the tubes at 6.3 V, .3 A like everybody else. It is doubtful that the heaters were any different than those used originally, they just previously rated them at the max voltage of 7 V instead of the usual design center average 6.3 V
Of course it was also a way to differentiate this new line of tubes from the competition, so there was probably some marketing considerations involved.
In later manuals, Sylvania just rated the tubes at 6.3 V, .3 A like everybody else. It is doubtful that the heaters were any different than those used originally, they just previously rated them at the max voltage of 7 V instead of the usual design center average 6.3 V
