[JJ15k]

Anybody has experience with these tubes? I just got a pair of 845Cs, my amp has an adjustable mA rating bias and I was running them at around 80mA, evrything seems fine but when I turned the amp off, I noticed the metal plate had a red glow (went away pretty quicly). Now I heard those models had some problem with dissipation so I was wondering if something was wrong

 

[aerius]

From http://www.high-endaudio.com/RECENT.html

Quote:

Despite my high hopes, the 845M did not sound as good as the 845C. The good side of this disappointment is that the 845M has 115 watts of plate dissipation compared to the 75 watts of the 845C. 845s have traditionally had about 90-100 watts of plate dissipation. Thus, these new tubes should last much longer than lower rated tubes. Also, the internal structure of the 845M should be less prone to mechanical failure. This has been a problem with the 845C.

Which means you'll have to drop the bias lower to keep it from overheating.

 

[JJ15k]

Is there a performance hit when lowering the bias?

 

[aerius]

The amp will have slightly less power when the bias is dropped, but the tubes will last a lot longer. Glowing red plates are usually a bad thing.