Your tubes are fine. Older 12AX7 variants made by Phillips or under license from them exhibit this effect - a bright filament on startup and then dimming down to normal as the tube warms up.
Newer 12AX7A tubes have a more controlled startup and don’t exhibit this behavior. The A suffix stands for controlled filament warmup.
Tom
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Main System:
Amati Futura Mains
Amati Homage VOX Center,
Proac Response 1sc Rears,
Three MC2301's for L,C,R
MC 602 for the rears
C 1100, MX 151, MCD 1100, MR 80
Nottingham Dais with Wave Mechanic
Sumiko Palo Santos Presentation
SurfacePro 3, RPi 4, ROON, WW Starlight Platinum USB, Schiit Yggdrasil, Benchmark DAC3 HGC
MX 151, OppO BDP-95, JVC RS-500 DILA projector, 106" diagonal Stewart Luxus Screenwall Deluxe with Studiotek 130 G3 material.
Lake House:
Ohm F, MC 275V, C2300, MR 77, Rega P3
OnDeck:
McIntosh MAC 4300v
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