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Re: Correct Bias for 1964 Deluxe Reverb?! Thanks!

11/19/1999 5:47 PM
Re: Correct Bias for 1964 Deluxe Reverb?! Thanks!
Yeah, I agree about the 70% dissipation guideline, but does this apply to 6V6's in Fender (Deluxe's, Princeton's,etc). Most feel that you loose your tone lower than 25ma's, in fact most that I've talked to like them set very close to max dissipation?  
11/19/1999 9:37 PM

Setting the idling current near max recommended dissipation in a class AB amp may be ok for some folks, if they normally play it at lower volumes. But there's no headroom, and the tubes will distort heavily and overdissipate when called on to play loudly, or produce maximum audio power. The tube needs time to cool down between each half-cycle. You can't just keep heating the plate structure and expect it to last. Whatever heat goes in needs a certain amount of time to get out, or the internal temperature will have a net increase before the next additional pulse. Duty cycle??  
People that understand tube circuitry, those who are concerned about reliability of their equipment, balanced with acceptable tone throughout the amp's intended operating range, and/or people that repair & service amps, will usually agree with the general (and safe) recommendations as those you found on Randall's site.  
Go ahead. Run your tubes hot. Get great tone at low to moderate volumes and possibly acceptable tube life. But don't expect the tubes (and possibly your output transformer) to last as long when the amp is pushed. Oh, it might sound awesome for a while. Then you'll have to open your wallet again, while your tone monster is in the hospital.
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