Bias question

[Wagster]

I've noticed on my Mod50 that the bias between my tubes are always outta whack. My Sovtek 5881's are 12mA off, my TS 5881's are 9mA off and the TS 6550's I just bought from Doug's Tubes are 10mA off. I'm wondering if it's not the tubes and something else? Does anyone have an idea of other things that could cause this? I'm left scratching my head

 

[FastRedPonyCar]

the tubes aren't properly balanced/matched. It's not a huge deal unless they are grossly different from each other but most amps can handle the tubes not being perfect and most people won't notice a difference in the sound with that degree of variation you listed.

 

[warlok1965]

I got a matched pair of TS 6550s from Doug's Tubes for my Mod50.... when I put em in and adjusted the bias they were about 1 mA apart. A couple of months later I checked them again and they were more like 12 mA apart! I found if I let the tubes warm up for 5-10 minutes and then take the readings, they are a lot closer (4-5 mA difference). Don't know what that all means, but I'm not going to worry too much about it.