You know how when you switch off a valve amp at the mains it keeps playing? Well.....

[TheDecameron]

My 509s keep ggggoing surprisingly long when the mains is disconnected and fade fade out symmetrically. I noticed that with my big Yves Cochet power amp, one channel goes off almost immediately and the other after about five seconds. Could this be the result of one side of psu caps being past it? There are eight el34s on this beastie and eight "C.E.F CAT-FRS" 100uF 450v electrolytics on it.

 

[Drzoigberg]

Same happens on my ncc200 dual mono power amp (1 channel off way before the other) I have always thought I was the side with the led attached


Jim

 

[stevec67]

I would have thought this is likely to be caused by a difference in bias current across the 2 channels, where one side drains away faster. Anyone confirm or deny this?

 

[Vlad_Bath]

May I bring to attention that it is best to avoid playing music though the valve amplifier after its power was swithced off. This results in cathode stripping because the AC heaters are off when the power switch is flipped, while the negative tention on the grid and the B+ on anode still present due to the power supply capacitance and forces the rapidly cooling cathodes to emit electones. This results in drastic shortening of the valve lifetime.
As for the reasons for one channel to die off before the other, it depends
First, is the amplifier dual mono or does it have a common power supply? If it has a common supply then most likely the PS caps are not to blame, and the reason lies somewhere down the chain, like the operating points of the valves - have you adjusted the bias recently? And are the valves equally aged/worn?
I would agree with stevec67 that bias current difference may be a very likely reason.

 

[YNWOAN]

I would have thought this is likely to be caused by a difference in bias current across the 2 channels, where one side drains away faster. Anyone confirm or deny this?

Yes, that is likely to be the cause in my opinion too.