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In Reply to: Re: BIAS problem ??? posted by TJL on April 26, 2007 at 03:01:28:
Thanks,I can see now that it is more a feature than a problem, it doesnt happen always and it varies from one channel to the other, or nothing at all, so I will just turn volume down before I switch-off the amplifier...
Antonio Melo Ribeiro
Follow Ups:
Less plate current means higher negative bias to grid, it can be have more ability to suppress the unstable status,
also if supply voltage Vsg of screen grid too high will causung this problems, El34 can withstand higher B+ than KT88 also get high power output from this smaller tubes, I use only +280V regulated Vsg for EL34 and 30 ma of plate current for pushpull 55 watts output to 8 ohm speaker.
The built-in meter shows mA, so I have no idea of the supply voltage...In the manual it is recommended 40 to 45 mA, the seller set it to 30mA, I tried 40mA, but in a quick test diddnt hear any difference, so it is back to 30mA, less switch-off noise, maybe later I will try again higher bias...
Antonio Melo Ribeiro
Sound quality from setting 30mA to 45mA Ip are nearly no difference,even using distortion meter to check it when working at pushpull mode, but maximun power output will dropping may be 20% at 30mA status.
But if at single end mode, higher plate current means lower negative bias and also lower distortion lower life time of tubes.
It is pushpull...Well, my speakers are 96db, so power is not an issue, actually at the same pre volume it is louder than the more powerfull KT88 amplifier I had before...
If I have a party I can always bump the bias... ;)
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