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previous: Jim O Im refering to the 1k-5watt screen ... -- 11/20/1999 7:06 AM view thread

Re: Screen Grid

11/21/1999 3:08 PM
Randy Jamz
Re: Screen Grid
I don't know exactly the rationalization behind anyone's thinking, even my own sometimes. I do know that there are more technically 'correct' ways of using the EL34 more efficiently and safely than Marshall ever used. But part of the Marshall sound was the fact that their amplifier was designed 'on the edge'. They switched over to 6550 in the U.S. to stop warranty claims due to tubes being eaten alive by SPL hungry rockers. Some technicians I know even use higher screen grid resistor values than 1K. You won't hurt anything by trying 2.2K. One idea I haven't tried myself is to run the EL34 as a true pentode by bypassing the screen with a capacitor. This will make the tube run a little more efficiently and last longer. The values suggested are 5K screen grid resistors with a 10uF/500VDC capacitor on each screen. I don't know how the sound will change after. A 'better' way to run an EL34 is to connect the supressor grid (pin #1) to the raw bias supply, and to connect all of the screens together through a common screen resistor. Mullard presented this idea in their spec sheets about 10 years before Marshalls came out. So who is 'right' is up for debate. It's your amplifier, and your ears.