• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

EF80/6BX6 glow on power up

I got these on ebay for an IF strip to replace 6EJ7's which had too much gain and lead to instability. They look nothing like a EF80 internally and don't look ever used. They work perfectly! Thing is when you first power them on you get an incandescent glow from the bottom of the tube which disappears about 2s as the heaters warm up. I've not seen this before is it some sort of heater protection?

https://www.worldradiohistory.com/h...less-IDX/IDX/70s/PW-1972-03-OCR-Page-0090.pdf
 

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