Topic: tube biasing

[BobW]

Or better yet, run them through a tester, if you can find one.......

I have a hickok 600A, the tubes test very strong still, so I'm pretty sure it is normal.  The entire quad does it not just an individual tube...

Nice !     

[ducati]

Back to biasing...  I just installed a fresh Quad (same tube family, 6550, but different brand) last night and watched the bias during the 20-min warmup:

0 min: 43mv
2 min: 44mv
10 min: 47mv
15 min: 47mv
20 min (ARC's recommended warmup time): 47mv

So in my case it looked like bias changed the most during the first 10 mins, but still only drifted by 10%.  Therefore, I think the idea of biasing them at 0 min and then again after recommended warmup time is a fairly good one...  Bias for my amp is supposed to be 65mv, FWIW.

On the blue glow...  I have never had a power tube that *didn't* glow blue to a varying degree. 

[pfife]

maybe relevant, maybe not, but the only way I can contribute to the convo - but in a guitar tube amp,tubes glowing blue are not a good thing.