I noticed on my solid state amp the clipping performs the same as you shown here, top cuts first. Service manual says adjust for even clipping at full volume. It has a 100k clipping adjust resistor near the start of the amp stage.
Biasing concepts have been shrouded in mystery for many many years. Much of it comes from the vendors saying untruths about their amp design. Vox is one such vendor; there are many others though. Cathode biased amps are really neat in a few ways. One is that you can essentially bias them as if they were class-A, and they will survive. Mainly because as you play louder and louder, the bias will actually cool off more and more. The biggest concept to grasp is that Cathode biasing does not = Class-A operation. Class-A operation can only exist in single ended designs. If you play loud enough, at some point, no matter how hot you bias a cathode biased, Push-Pull amp, the bias will cool down enough to operate in Class A/B. The big thing to remember is that in Class-A, the tube NEVER shuts off, and is conducting 100% of the time. In Class-A/B, one tube or the other is in cutoff ( not conducting ) for at least some amount of time. If a tube is in cut off, even for a fraction of a second, it is not Class-A operation, period. For cathode biased, push-pull amps, I shoot for about 95% of PD ( plate dissipation ). Much more and you stand a good chance of burning things up permaturely. Anything less than 90% of PD in cathode biased amps is probably going to be too cold, and Crossover distortion will be prevalent. Crossover distortion is the sign of an amp biased close to, if not in Class-B operation. Randall Aiken's White pages are good resource for dispelling myths and BS. There are many old wives tales that exists. And it is true, you can pull all but one power tube in a 100-watt, 4 tube power amp, and it will operate just fine.
Obviously you have come to the same conclusions I have but long before I did. I'm surprised that other amp guys like the Guitologist and Uncle Doug have not mentioned this. Maybe they have and I just have not seen the particular video. One thing though and that is that there are not very many cathode biased push pull amps. I will have to look at some older Vox stuff. Great comments. Thanks.
Great demonstration! I usually shoot for 95 to 99% on a 5e3. I don’t recall ever looking at the scope when checking cathode bias, but I will next time. And yes, crossover distortion sounds nasty. Cool little signal generator - thanks for the tip on that!
I noticed on my solid state amp the clipping performs the same as you shown here, top cuts first. Service manual says adjust for even clipping at full volume. It has a 100k clipping adjust resistor near the start of the amp stage.
Biasing concepts have been shrouded in mystery for many many years. Much of it comes from the vendors saying untruths about their amp design. Vox is one such vendor; there are many others though. Cathode biased amps are really neat in a few ways. One is that you can essentially bias them as if they were class-A, and they will survive. Mainly because as you play louder and louder, the bias will actually cool off more and more.
The biggest concept to grasp is that Cathode biasing does not = Class-A operation. Class-A operation can only exist in single ended designs. If you play loud enough, at some point, no matter how hot you bias a cathode biased, Push-Pull amp, the bias will cool down enough to operate in Class A/B. The big thing to remember is that in Class-A, the tube NEVER shuts off, and is conducting 100% of the time. In Class-A/B, one tube or the other is in cutoff ( not conducting ) for at least some amount of time. If a tube is in cut off, even for a fraction of a second, it is not Class-A operation, period.
For cathode biased, push-pull amps, I shoot for about 95% of PD ( plate dissipation ). Much more and you stand a good chance of burning things up permaturely. Anything less than 90% of PD in cathode biased amps is probably going to be too cold, and Crossover distortion will be prevalent. Crossover distortion is the sign of an amp biased close to, if not in Class-B operation. Randall Aiken's White pages are good resource for dispelling myths and BS. There are many old wives tales that exists. And it is true, you can pull all but one power tube in a 100-watt, 4 tube power amp, and it will operate just fine.
Obviously you have come to the same conclusions I have but long before I did. I'm surprised that other amp guys like the Guitologist and Uncle Doug have not mentioned this. Maybe they have and I just have not seen the particular video. One thing though and that is that there are not very many cathode biased push pull amps. I will have to look at some older Vox stuff. Great comments. Thanks.
Great demonstration! I usually shoot for 95 to 99% on a 5e3. I don’t recall ever looking at the scope when checking cathode bias, but I will next time. And yes, crossover distortion sounds nasty. Cool little signal generator - thanks for the tip on that!
@@MikeM-Colorado Finishing up on a AA764 and discovering some interesting issues. Should post it up within a few days.
Thanks for the comment.