It was part of a matched quad....doh!
Martin, I'd get my money back for those tubes, they clearly weren't matched very well since you didn't light all of them up at the same time
Seriously, it could be a problem in your amp or more realistically cheap tubes. I'm betting the latter. I'll probably spend a month with mine, if they last that long, before I try swapping them out.
One of these days I am going to get into some serious tube swapping, just not yet.
HT - Sunfire TG IV, Sunfire Cinema Grand Sig. 400 x 5, Oppo 93, Klipsch LaScala (3), Cornwalls (2), SW-12, Sony 60" LCD
2 channel - AN L2 Pre-amp, AN Interstage Mono Blocks 300b PSE, AN 2.1 DAC, DUAL CS 5000 TT, Oppo DV-981HD, Lowther PM4a/Azurahorn/SentryIV
2 channel - AN L3 Signature Line stage, AN Interstage Mono Blocks 300b PSE, AN Sig. DAC 3.1 , AN Sig. Phono Stage, Sota Comet TT, Altec A5's
2 channel - Carver VTA20 Baby Black Beauty, Custom Line Stage, Klipschorns
2 channel - AN Interstage Mono Blocks 300b PSE, Carver C-5 Pre, Altec A4 speakers
2 channel - Audio Note Kit 1 300b SET, Audio Note DAC 2.1, Altec 288 Horns/JBL Bass bin