|24th June 2011, 06:45 PM||#1|
Join Date: Jan 2011
Why run the tubes so hot (over limits) ?
I said I wouldn't tinker with my three-month-old SSE until winter came - guess I don't score highly for 'willpower' - it's got the better of me!
I have read in other threads that some people, Tubelab.com in particular, run their power tubes above their spec'ed dissipation (e.g. 40-50W on a KT88 rated at 35W max). I am curious as why people do this...
1) More volume?
2) Better sound?
I am genuinely curious - I run my KT88s at 31W, for no other reason than it was a convenient value that was below limits - I know no better.
I can understand if it's to eek as much volume as possible...Most posters here seem to be from the US, where houses tend to be bigger than where I am in the UK and maybe you have a big room to fill with sound, so every last Watt is important.
I have two cathode bias points - one for EL34 and one for KT88. Both are conservative. I can run the EL34 at 21W or 26W (published max 25W) depending on where the switch is. I can't tell any difference in the sound at all between the two.
If the reason for running them hot is for improved sound quality (i.e. lower 2nd harmonic distortion?), isn't this 'pleasing' distortion what attracts us to singled-ended amps in the first place?
|24th June 2011, 10:13 PM||#2|
Join Date: Jul 2005
Location: West Virginia panhandle
On some speakers or music selection the improvement may not even be noticed. On my Silver Iris open baffles cranking up the current really cleans up the bass. I run my EH KT88's at 100 ma each when I use these speakers. I run less current on my small speakers. The original tubes are still in the amp and I bought them used for $20 each, so I have got my moneys worth from them.
Set your bias at whatever value that suits your taste. Higher current will reduce tube life. I have a cathode resistor switch and it makes a difference in some cases.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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