ohh... you again (shakes fist), It's alright though, I like you anyway.
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Originally Posted by MajorNut1967
[COLOR="Lime"]In your experience! Well why don't you explain the vastness of your experience with this particular amp and why sticking with the stock values is not necessarily a good thing?
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You can keep with stock values all you want, but there is also nothing wrong with increasing the value of the screen resistor/stopper than the minimum required to do the job. regarding wattage, There seems to be two schools of thought, the ones that will use the bare minimum wattage, and pray this resistor acts as a fuse in some cases (which in the experience I have often fails to do so, or does after it is already too late), and the ones who advocate using the highest practical wattage you can find to protect against overload as well, where an undersized screen resistor is likely to burn and Arc, not pop.
If you are hoping this thing is going to act like a fuse, you have to pick a type of resistor that does indeed pop open, and not prone to arc. Not all types of them will pop! 2W is the bare minimum I would use.
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Originally Posted by MajorNut1967
But what you didn't think about is if the was an instance of parasitic oscillation or a lead dress problem! And that if there was parasitic oscillation going on guess what one of the first things to get roasted would be? Does 470 mean anything to you?
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The primary function of the screen resistor is to limit screen current, in order to bring it/them to a happy working condition throughout the swing of the valve under signal conditions. 470 does mean something to me, it most likely was the minimum value chosen to provide what I said above, with a bit of safety built in for those operating conditions, for that valve type, and retain output power at the same time. If you really want me too, I will post the math on what the minimum value for 6l6 types under those voltages are. There is no wrong or right value depending on what you are designing around, and you can certainly go higher if you want to (just not lower than the minimum considering some built in safety), and like the sound. In other words just because it is a 5881/6L6 valve doesn't mean it needs a 470r screen resistor. 1K is perfectly fine.
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Originally Posted by MajorNut1967
The thing about parasitic oscillation is that it is usually in an upper frequency range that you would never be able hear or detect, much less diagnose. And I know you're going to come up with that, "the likely-hood of that happening in a production amp is zero to none!" Well how do you know?
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The grid stoppers typically are more responsible for damping that, and yes those should be there!, most older marshall type amps are pretty unstable with out them. There are other causes of oscillation too that most people don't consider... like the use of -fb. Most amps come dangerously close to oscillating due to an unstable feedback loop when using more feedback then they can, and I would say that most amps do ring ultrsonically.
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Originally Posted by MajorNut1967
So Joey, the engineers at Fender used those values for a reason and I trust that they know or knew a lot more then you do!
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I would say that the engineers at ATT/Western electric knew more.