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previous: Chris Harden I've been mulling over some other w... -- 7/8/2000 8:34 AM View Thread

Re: Alt. methods of driving power tubes

7/8/2000 11:10 AM
Ray Ivers
Re: Alt. methods of driving power tubes
Try the Ernie Ball Music Man site, and check out the power amp design on the 2100-RD:  
Winnie Thomas has noted that the .pdf and .zip files are different on some of the amps, you might want to download them both. This power amp design is basically a cascode (cathode-drive) arrangement. I have had people tell me that the driver transistors will dominate the 'sound' of this design, and the tubes are simply level-shifters; I disagree. When clipping occurs, it ain't gonna be the transistor that clips. All the same, I think I would use this design for a loud, clean power amp, not an 'amp-on-ten' overdrive.  
One thing I've always wanted to try is a push-pull triode-connected Class A 6V6 or EL84 driver stage thru a step-down interstage transformer to an EL34 pentode output stage, giving you the ability to really drive the hell out of those '34's. You could have variable B+ over a limited range on the (cathode-biased) drivers, which could be done simply with a high-wattage wirewound pot due to the near-constant current draw of the Class A design, and would give you some control over the balance of driver/power tube distortion. It would also be cool to have a dual pot (100K or so) connected as a dual variable resistance between the interstage secondary and the output tube grids; this would have relatively little effect when the output tubes were not clipping, but at soon as the grids started to draw current higher settings of this control would add compression and soften clipping, allowing more control of the clean/dirty thing at the guitar's volume knob (Peter S.!). A control like this would not have the same effect with a conventional driver stage.  
I would love to convert the Music Man circuit to use FET's, with a high(er)-impedance input directly to the drivers, and eliminate the op-amps; any thoughts, R.G.?