Firstly, this is my first post to Amp Garage, so hello everyone! I first posted this in a.n.other forum, but got few helpful responses.
This is probably old ground, but please allow me to get some current thoughts: My guitarist has a 1971 Fender Super Reverb with a solid state rectifier mod, and a B+ of 490V biased to ~37ma cathode current- I’m a bit worried the Chinese 6L6GCs in it may expire (the original Fender valves ran fine for years)- I am looking for 6L6GC valve suggestions for this quite high B+; I would probably like to get dissipation up a bit also to, say 43ma@70% (according to http://www.ax84.com/biascalc.html?Bvolt ... ction=calc)?
+1. 70‰ is the maximum "safe" dissipation, not the "best" number. The higher you go, the longer the amp operates in the Class A region (lower output, but possibly better 2nd order harmonic distortion). Fenders, I've found, like to be as close to 50‰ as you can get them without x-over distortion.
The amp is not mine and the owner definitely has liked the current sound over the years so won't want any big change; I could suggest a drop of 10-20v from a zener and set a new set of tungsols at 60% and see what his ears say. Then hope the tubes last as long as the old faithfuls- well over ten years!
Firestorm wrote:+1. 70‰ is the maximum "safe" dissipation, not the "best" number. The higher you go, the longer the amp operates in the Class A region (lower output, but possibly better 2nd order harmonic distortion). Fenders, I've found, like to be as close to 50‰ as you can get them without x-over distortion.
You're suggesting adjusting bias using the crossover notch method. Aiken's discussion of this method is worth reading:
Firestorm wrote:+1. 70‰ is the maximum "safe" dissipation, not the "best" number. The higher you go, the longer the amp operates in the Class A region (lower output, but possibly better 2nd order harmonic distortion). Fenders, I've found, like to be as close to 50‰ as you can get them without x-over distortion.
You're suggesting adjusting bias using the crossover notch method. Aiken's discussion of this method is worth reading:
Good link, but that's not what I meant. Aiken (I love Aiken) is one of the 70‰ guys. I'm more in line with KOC: 50‰ plus whatever you need to avoid ugly sound at full drive.
