Problem with biasing

Could be a bias resistor out of spec or bad pot.   

Try switching tube positions. Does the bright glow move? If not refer to @oddiofyl, if it moves replace the tube. 

Most likely a bad tube.  Swapping tubes will tell you if it is the tube or something internal.  a bias resistor has been suggested and that would indeed explain the reading but these resistors should last a lifetime.

Running at high bias current will ruin the tube, but it may already be there.

If indeed it is the position and not the tube, then don't run the amp until you get it fixed unless you have a big tube budget.

jerry

Right, I’ll check the tube today. 

It was the tube. I was able to bias them all to .97 volts… that right, what would that be in ma? I have 2 amps for a bi amp system. Yea one is in ma and the other volts? I like if they’re 85 ma

😊👍

Tube problems are not common, but if you get a whistle, bright tube, or weird poping, that is the place to start. Because most tube equipment uses more than one of the same tube, diagnose can take a couple minutes. 
 

My systems run over forty tubes and I get a strange sound every couple years or so… typically associated with a new or relatively new component. 

Wow, 40 tubes, that’d be expensive to re-tube I bet. What are you running?i

Hi Kelly.

My systems are shown under my user ID.

I have Audio Research Reference Phono stage, preamp, DAC/ CD player, and amps, Woo head amps WA6, WA6SE, WA 5, and a PrimaLuna integrated amp. I’m thinking about $100 in the last ten years. I had to replace the Prima Luna tubes, and I traded in my Audio Research Reference 5SE for a Reference 6SE before it needed new tubes.

So, I think this is why folks talking about the theory and reality of tubes are so far apart. I had a Sonic Frontiers tubed CD player for fifteen years… the cd transport needed changing out three times, the tubes, none.

I like the tubes, they are so much more

musical