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Class B amps

5/9/1999 4:08 PM
Bill Costello
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Class B amps
This might be another "newbie" question but I've been up and down the forum archive and no one seems to talk about it! I'm working one an old PA amp using a pair of EL 34's. It's running about 775 vdc on the plates and 400 vdc on the screens from a stiff supply. The bias voltage is -46 vdc. This appears to be Class B, and the amp's model number implies a 75 watt rating.  
After chasing links I've found curves for this sort of parameters but I've got a nagging worry. Why is it that no one runs Class B?  
Is it going to sound horrible? Will I get tube life measured in minutes? I'm building a classic Marshall preamp to drive the pwr tubes and I find myself wondering why whoever designed this amp used a 12AX7 at the input but used pentode 6AU6's for the phase inverter (2 of 'em, of course).  
I'd appreciate it if someone can give me some advice before I spend a lot of time and effort only to get an insurmountable problem or disappointment when finished...

 
Replies:
Graywater Bob,Years ago Class B amps ... -- 5/9/1999 6:16 PM
SpeedRacer I don't have them handy, but I thin... -- 5/11/1999 10:29 AM
Jim S. The engineering design decisions ma... -- 5/11/1999 11:14 AM
Ned Carlson What you're describing almost sound... -- 5/12/1999 7:54 AM