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6l6 and el34"s


 
3/25/2005 4:04 PM
scole 6l6 and el34"s
whats the best way to setup a fender type amp to run el34's or 6l6 power tubes?
 
3/25/2005 5:59 PM
Aharon
EL34s need more heater current for one.  
The bias will be diferent.  
What amp is it,what tubes are in there now?  
Aharon
 
3/25/2005 7:49 PM
scole
its a 5f4 super diy, i already have the tube sockets wired for both tubes, i wonder if theres a way to wire the bias circuit to handle both. the power tranny is designed for el34's.
 
3/25/2005 8:13 PM
Aharon
For fixed bias you can set it up that there's enough neg voltage to bias both tubes.  
For cathode bias you are going to have to find a resistor value that accomodates both.  
If it's set up for EL34s then pin 1 is grounded already.  
Aharon
 
3/25/2005 8:31 PM
scole
is that possible? to find a resistor value for both.
 
3/25/2005 11:10 PM
Carl Gigun
sure, they're not so different and there's a big range in a class AB amp for an "acceptable" bias point. As long as your resistor is large enough to keep each tube safe you're okay. If your plate voltage is pretty typical you're probably looking for about -30 to -40 volts bias. You'll get people saying "if you bias them too cold they won't sound good", but your ears will tell you if they sound good or not.  
 
I doubt you'd change tubes very often though so you don't really need to find a bias voltage that works for both tubes. I'd just rebias whenever I switched tubes. I'd do that even if wasn't changing tube types, just replacing some 6l6 with new ones etc.  
 
-Carl
 
3/25/2005 11:33 PM
Aharon
I built a P1Extreme form the Ax84 site.  
That amp can accomodate various tubes like EL34,6L6,KT66 etc.  
The design calls for a 330 ohm cathode resistor and a plate voltage of around 380V.  
I just wired my OT in a way that I have 5K for 6L6 and 2.5K for my EL34.  
This is a SE amp.  
Aharon
 
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