This discussion led me to think first time ever about the difference between cathode bias vs fixed bias. So I read some articles and it dawned on me. The cathode bias has this resistor between cathode and ground. It will do TWO things - only one was discussed on those articles. The obvious thing is that it raises the cathode DC-potential to i.e. +20V - then it appears like -20V relative to grid. The other thing - that was not discussed in those articles - was that asyou play louder - the current increases - raising the voltage-drop across that resistor = altering bias. Maybe they mentioned it, but not in these words - they used terms, that described the sound.
Fixed bias would be more clean and precise - cathode bias would be creamier.
This leads to a question : is there an amp with partially both? A smaller than required cathode resistor + fixed bias. This might be a compromise between the problems of fixed-bias overheating and too clean sound.
Maybe a bias-feedback circuit? A fixed-bias amp w loudness-dependent bias feedback?
Back from today's road trip - that included my first ever meeting w Guild amp
And yes - quick researh reveals some amps that have both - cathode resistor + adjustable bias - a.k.a. fixed bias - ( funny - isn't it
)
Some Fenders - some Guilds - to begin with.
And since I mentioned that I first time in my life got to play a Guild Amp - here are two pictures.
The latter one shows the master volume control knob - the metal disc is being pushed in - I suppose it should be flat on top like on other knobs.
