@mamifero "I am not very familiar with Variable or Autobias -I'll google it- but I
am sure it's not autobias. It has manual adjustment and built-in meter
instead, each tube has a knob and -according to the manual- the needle
on the meter should be placed in the middle."
Thank you for including this. You're amp is fixed bias, which means it's adjustable, and is a counterintuitive name if there ever was one, but we won't go deeper than that here. The first thing you should do is bias the amplifier. You'll ensure the tubes run at the recommended setting, and also potentially find any defective (they won't bias properly) tubes in the amp presuming you don't have a tube tester to check them. Again, if the output tubes are biased cold, the amplifier will sound less warm, romantic, and good. That said, the vast majority of manufacturers recommend too cold a bias setting in the name of preserving the output tubes. People love to brag about how long their tubes lasted, and praise their amplifier itself and the ability or brilliance of its designer, though it's mostly a reflection of the bias of the output tubes. For me, in for a penny, in for a pound. I buy and build tube amplifiers because properly designed, implemented, and run, they provide me more satisfaction than most solid state amplifiers. I absolutely will not sacrifice that for more tube life.
After single-ended versus push-pull output stage, I feel fixed versus cathode bias represents the most important factor in the character of an amplifier in terms of sound, response, feel, etc. Fixed bias is more direct, immediate, fast, and tight. And because of that, more prone to the complaints you raised. Rectification, front-end topology, and tubes shift a fixed bias amp away from those characteristics. So after you bias the amplifier, presuming you still want a more romantic sound, it's smart of you to have come here seeking out different tubes as it's the one area you can easily change
Thank you for including this. You're amp is fixed bias, which means it's adjustable, and is a counterintuitive name if there ever was one, but we won't go deeper than that here. The first thing you should do is bias the amplifier. You'll ensure the tubes run at the recommended setting, and also potentially find any defective (they won't bias properly) tubes in the amp presuming you don't have a tube tester to check them. Again, if the output tubes are biased cold, the amplifier will sound less warm, romantic, and good. That said, the vast majority of manufacturers recommend too cold a bias setting in the name of preserving the output tubes. People love to brag about how long their tubes lasted, and praise their amplifier itself and the ability or brilliance of its designer, though it's mostly a reflection of the bias of the output tubes. For me, in for a penny, in for a pound. I buy and build tube amplifiers because properly designed, implemented, and run, they provide me more satisfaction than most solid state amplifiers. I absolutely will not sacrifice that for more tube life.
After single-ended versus push-pull output stage, I feel fixed versus cathode bias represents the most important factor in the character of an amplifier in terms of sound, response, feel, etc. Fixed bias is more direct, immediate, fast, and tight. And because of that, more prone to the complaints you raised. Rectification, front-end topology, and tubes shift a fixed bias amp away from those characteristics. So after you bias the amplifier, presuming you still want a more romantic sound, it's smart of you to have come here seeking out different tubes as it's the one area you can easily change