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Re: Orange glow on power tube plates?

5/1/2004 6:29 PM
Wild Bill
Re: Orange glow on power tube plates?
Steve, it almost certainly is a bias issue!  
Bias sets the idle current to the correct value for the tubes. If the idle current is too high then you get orange or worse yet red or even white spots!  
A slight bit of orange is mild enough that the tubes won't likely fry before your eyes but you are kicking the crap outta the expected lifetime of the tubes.  
Bias should ALWAYS be checked and if necessary adjusted when changing output tubes! They're just too expensive if the lifetime ends up in months instead of years. In the old days tubes were tighter in spec when manufactured and often you could get away with just changing them but not today.  
If biasing wasn't a good idea why would they put in a bias adjustment control for a tech to tweak?  
---Wild Bill

Steve Thanks Bill. I think my Princeton has fixed bias.... -- 5/1/2004 10:53 PM
g1 Re: Orange glow on power tube plates? -- 5/1/2004 10:55 PM