Different strokes...
Scottone said:
Thanks, that must be where I read about it. I have picked up most of Kevin's books over the years.
Actually, I stopped worrying about that. The "tone-lizard" has some great info on his site about how adding screen resistors changes tone. The earlier amps often didn't use any screen resistors at all!
The purpose of any screen resistor is to limit the screen current to a safe value if the tube is getting pushed real hard. As the screen current increases the voltage drop across the screen resistor will also increase, throttling down the gain of the tube somewhat. The problem with high values of screen resistance is that you get bigger screen voltage swings with the signal, adding a lot of non-linearity to the output waveform.
Mind you, I'm the last guy to champion worrying about hifi factors like linearity with a guitar amp (who wants a hifi sounding guitar amp?) but a 1k screen resistor seems to be pushing it, IMHO. There's other ways to protect the screens.
What seems to me more important is the Traynor/HiWatt trick of breaking the suppressor grid connection with the EL34 to the cathode and instead tying it to the bias supply to make it a bit negative with respect to the electron flow. It does seem to make the tube work better and they do seem to last longer. I'm often impressed with finding an old Traynor with old tubes that still show good life!
Almost anything we do will change tone somewhat. Tone is a matter of personal choice - we just have to learn what changes what and what the customer likes!