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In Reply to: is G2 limit at 300V a real problem? Re: CV4060 in place of KT88 posted by wlee on August 26, 2005 at 01:25:09:
...as a triode YES . UL or pentode , well , the risk is yours . Probably better not to try this with expensive NOScheers
...FB
Follow Ups:
hi FB,Sorry I meant most amp are designed that way, my Dyna SCA 35 is running at 350V UL for EL84, and mnost 6L6GC, 6V6 used in penthode or UL at well above their G2 rating... Just wonder why every one designed that way.
Also I wonder how the G2 voltage effect the sound, it seemed that at G2=350V for KT88 sounded more or less the same as G2=400V except tat the bias is lower at 350V...tks and best rgds
William Lee
Hello ,
Remember voltage drop across the output transformer , these designs may be cathode bias so the overall anode/screen to cathode is probably a lot lower than you think . Fixed bias is another matter , as long as you can dial in more negative bias at higher screen voltages you should be ok , may be an idea to gradually measure and rebias as you increase the screen voltage . I think 6L6GC have higher screen grid ratings ratings than a 6L6 :)ps I forgot to mention . CV4060 can be strapped as a triode with either the beam plates tied to the anode or the cathode , like what can be done with an EL34 . I prefer G2 and beam plates tied to anode via a 100r resistor , if you try asa triode consider both :)
cheers
...FB
hi FB,Tks and yes, the cathode voltage did reduce the G2 voltage... But still in many amp they really pushed the tube with G2 much higher then rated, just wonder why. In the SCA 35, the B+ is in the order of 350V while cathode is about 20V. But the tubes did last for some time.
I have tried to use different G2 voltage and to me, the sound did not seemed to change. So now i am using G2 of about 350V for EL34/EL37/KT88 to amke sure the tube will last longer.
I am quite sure now that pentode output sounded better then UL...
Will try triode connection one day!tks and best rgds
William Lee
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