Looking for advice, if you please.

[soundguruman]

The best amps had sliding wire wound resistors to adjust for the tube and the line voltage variation.
You wanna adjust it to produce equal clipping plus and minus with a clean input, at least adjust it "that" much...
but I would rather adjust the cap value too.

[Steve Conner]

Guitar amps are just a clever way to operate tubes poorly.

Fixed that for you!

On my amp I found that I could turn the screen voltage down nearly to zero, and the clipping (from the overdriven power tube) was still reasonably symmetrical. That says to me that the cathode bias self-adjusts reasonably well.

The required value of cathode bias resistor probably varies as the one-half power of the line voltage, or some other ridiculous piece of math.

[Chuck H]

Hmmmm... I was going to say "thank you" but that button seems to be missing. So you get a "like" instead. Because I agree. And it's good to know the cathode bias is so forgiving for this application.

[J M Fahey]

Still, if cathode bias was truely self adjusting such that you could scale the voltages down quite low without bias consequences then why do we bother to choose a particular value resistor for a particular amp? One resistor value could be used for all amps in all instances!?!

Please do not mix different things.
1) *different* tubes in *different* amps require *different* cathode bias resistor values, optimizing bias current according to particular needs.
2) once you settle for a given value in a particular amp design, turning +B voltage down is accompanied by a *reasonable* bias self-adjustment.

[tonequester]

being in over your head forces one to attempt to swim

Please do not mix different things.
1) *different* tubes in *different* amps require *different* cathode bias resistor values, optimizing bias current according to particular needs.
2) once you settle for a given value in a particular amp design, turning +B voltage down is accompanied by a *reasonable* bias self-adjustment.

tonequester here.

soundguruman. I have to admit that I've become out of my league, as this discussion has progressed. I am learning alot. However, I am slow to bone up
on as much info as has been presented here so far, especially when there are some varied opinions. I have come to only one conclusion which I believe to be an absolute,
that being ...if there IS a science of tone. It is more a matter of opinion, than a matter of science. That being said, your recent comments make sense to me. I was impressed
by your thought about adjusting for equal + and - parts of the clipped signal. I believe that Chuck H made a good point on the probable limitations of cathode bias(everything
has it's limitations outside of God). I thank you both for your input and providing ideas for me to check out further. Steve Conner. I find your results concerning reasonable clipping symmetry while using close to zero screen voltage to be welcome news to me, as I am considering going that "route". I wonder if it is a given, if one would see the same symmetry with a similar increase in screen voltage of the same proportion ? Just curious. I love your comment on "rediculous mathematics", mostly because my own math skills are rediculous "in the negative". Thanks so much for the reply. JM, I appreciate your pointing out that "different tubes in different amps", and the mixing of tubes in an amp has serious consequences that have to be addressed properly. I will resist any temptation to do so. I detest smoke and fire, especially when it comes from any of my equipment. This has been a great discussion, and I have picked up on some good info with quite a bit more to further investigate. Lest I forget, thanks also to Gibsonman63 for the lead on VVR by way of hall Electronics. Happy to make your "aquaintance", and I WILL check it out. I would like to think that the 5 star rating somebody has applied to this discussion means that the content is A+. I'm pretty sure that this is the case. However, a part of me is thinking that alot of people are having a riot at the
stupidity of yours truly. As usual, you guys are great. Thanks for your time and participation. tonequester.


Quote : "Hell, there are no rules here....we're trying to accomplish something here ! Thomas Edison.



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