How to test output transformer performance for overperforming amp

[nsubulysses]

Yes the feedback network. I think I am also reaching power stage distortion and that also contributes to the grainy sound and lack of ability to control it with the tone controls. I recently increased my feedback resistor from 110k (16 ohm tap) to 150k and it tightened up the sound and removed s bit of that unpleasant distortion characteristic. It also allowed me to add bass in the preamp in ways I wasn't able to before because it made the sound too flubby.

Going back to post 7, can anyone say why my input signal begins to distort when my power stage does ? This is really weird to me. I should check a bunch of other amps this same way to see if that happens

[Dave H]

Going back to post 7, can anyone say why my input signal begins to distort when my power stage does ?

Check the grounding of your test set up. It could be that the load return current is running through the scope or sig gen ground.

[J M Fahey]

Hmmm, not sure what information can be gleaned from this scenario but I built this amp ...............................

Sorry but that is a long thread , it shows 4 or 5 amp schematics and half a dozen circuit snippets, lots of changes along the way, can you please repost here the *one* schematic you actually built and are asking about?
Thanks.

[J M Fahey]

Going back to post 7, can anyone say why my input signal begins to distort when my power stage does ? This is really weird to me. I should check a bunch of other amps this same way to see if that happens

I have a couple ideas at the tip of my tongue, but can´t comment until I´m certain about the exact circuit of your amp and a detailed description at how and where you are injecting your test signal.

And yes, I *have* seen amps where drive signal distorts at about the same time as power tubes clip, but there´s 3 or 4 possible scenarios, would love to focus on yours specifically.

[nsubulysses]

Hi JM, I will draw the schematic. I am out of town for 2 days but I'll try to do it on Sunday and post it. I would love to hear your thoughts

thanks

[nsubulysses]

Last night I tried to draw the schematic. It took over 10 minutes to find a piece of paper. When I did, I realized all the pencils I had were so old that the eraser was so dried out it could no longer erase, merely just smear lead all over the paper.

I'll have to try again today and find some better materials

[eschertron]

Last night I tried to draw the schematic. It took over 10 minutes to find a piece of paper. When I did, I realized all the pencils I had were so old that the eraser was so dried out it could no longer erase, merely just smear lead all over the paper.

I'll have to try again today and find some better materials

...and write a blues song about your soul-crushing experience with the pencils and paper

[nsubulysses]

Ok JM I just need you to fax over your signed NDA otherwise all rights and access to materials that involve helping me will be revoked

Preamp
Power/output

[Justin Thomas]

Just out of curiosity, how can the negative bias supply be derived from the B+ DC voltage? Wouldn't a reverse diode there just block the positive DC entirely? Wouldn't the bias supply have to tap from the AC portion BEFORE the rectifier?

Justin

[nsubulysses]

Thank you Justin. You are correct

I drew it wrong. keep em coming. Although it should be mostly correct other than that I think. Please allow me to eat my words if anything else looks weird.