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12ax7 power requirements


 
12/1/2004 12:56 PM
angelo
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12ax7 power requirements
Ruetz and the real Mc tube guy have these preamp power supply ideas involving common "wall wart" plugs you can find anywhere.  
Ruetz goes on to say:  
 
"The step-down PT needs to provide enough current to supply however many 12AX7s you plan to use, plus at least 100mA extra to feed the step-up PT."  
 
Well, how much current would 4 12ax7s need?  
 
I am trying to build a preamp test powersupply.  
 
The rest of Ruetz's article is here:  
http://www.diyguitaramp.com/preampps.html  
 
Thanks
 
12/1/2004 10:35 PM
Uncle Yarra
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If you're making a piece of test equipment,  
you want to be confident that it doesn't  
affect the equipment under test in a  
non-optimal way. So if you want to minimally  
power 4 12ax7's, you'd need 4 * 150mA @ 12.6V.  
 
What if you want to run the heaters at 6.3V ?  
Or have more than 4 tubes to heat ?  
Or a pre-amp that uses some other tube ?  
Or want to 'float' a tube or two at some  
elevated heater voltage ?  
 
That's when it's handy to have plenty of  
watts/other circuitry available.  
 
If, however, 4 tubes is the absolute maximum  
number of tubes you will need to heat, then  
600mA is enough.
 
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