Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: agent10508 on July 13, 2022, 11:56:16 AM
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During the glow test of the tubes, only the bottom of the 12au7 glowed while the top remained unlit. The stock tubes provided are labelled Beckman which I believe are rebranded Sylvanias. The main power tube glowed excellently, so should I be worried or is this just a quirk of the tubes provided?
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Whether the top and/or bottom glows depends on the position of the heater element inside the cathode sleeve, so if you don't see a glowing dot on the top of one side but you do see it on the bottom of that side, all is well and there's nothing to be concerned about.