Single Ended Amps - Opinions

[Tobyk]

you can have simple NFB like in fender champ,
but also better versions like Shade NFB , Local NFB Anode to grid on output tube, and Local cathode feedback on output tube. I will not say which works best you need to try all of them. If you start now in a few months you will have all the answers!

Sorry to keep nagging about this, but why is ”local NFB anode-to-grid on output tube” (”NFB1”) better than the usual Champ global NFB (”NFB2”)? Is it because NFB1 does its thing without affecting the rest of the circuit?

[bepone]

shade NFB doesnt take in account output transformer which is good thing..depending of the quality of OT you can have different effects when taking signal from speaker output, after passing the OT

[Tobyk]

shade NFB doesnt take in account output transformer which is good thing..depending of the quality of OT you can have different effects when taking signal from speaker output, after passing the OT

Thanks, so back to the Bassman – looking at it again I see the feedback actually goes all the way back to the previous plate, that would make it a Schade and not a NFB1, correct? Attaching schematic..

B71D7048-2FB0-4D2E-AB37-03E31E2CFC56.gif

[bepone]

yes this is shade, linearisation of 6L6 curves from tetrode to triode..220k anode 6L6 to anode 12AT7..
also there is second NFB loop is from spk. output to the PI

[Tobyk]

yes this is shade, linearisation of 6L6 curves from tetrode to triode..220k anode 6L6 to anode 12AT7..
also there is second NFB loop is from spk. output to the PI

Thanks, and a to make it a NFB1 I would instead connect it before the 6L6 grid stopper, is that correct?

[roberto]

Before the coupling cap.

[Tobyk]

shade NFB doesnt take in account output transformer which is good thing..depending of the quality of OT you can have different effects when taking signal from speaker output, after passing the OT

Does linearization of SE output tube make distortion similar in quality to PP or is it still inferior, in your opinion?

[nworbetan]

shade NFB doesnt take in account output transformer which is good thing..depending of the quality of OT you can have different effects when taking signal from speaker output, after passing the OT

Does linearization of SE output tube make distortion similar in quality to PP or is it still inferior, in your opinion?

Overdriving a SE output tube is still going to give SE harmonic content, but the transition from clean to overdrive is going to be more sudden with NFB involved. Which qualities are you looking for when you're deciding superior or inferior, in your opinion?

[dorrisant]

On this subject... Anyone have a suggestion for SE 6550? High-ish gain?

I was thinking this: https://www.cedist.com/products/transfo ... ended-30-w

Maybe 30W is not enough... Primary at 3K or 5K?

[martin manning]

What plate voltage are you thinking? AT 400V you would get something like 17W output power. The listings suggest those OT's will work with a 6550, even 2x 6550 in one case.

[dorrisant]

Probably 400v... Looking for PTs as well.

I am set on fixed bias though. Would have to derive the bias voltage from the HT winding. No biggie.

For roughly 400 on the plates with 3 novals... looks like 300-0-300 would be a hair above the target. So maybe Hammond 272FX. Maybe pair that with a 1630SEA?

[Tobyk]

shade NFB doesnt take in account output transformer which is good thing..depending of the quality of OT you can have different effects when taking signal from speaker output, after passing the OT

Does linearization of SE output tube make distortion similar in quality to PP or is it still inferior, in your opinion?

Overdriving a SE output tube is still going to give SE harmonic content, but the transition from clean to overdrive is going to be more sudden with NFB involved. Which qualities are you looking for when you're deciding superior or inferior, in your opinion?

@bepone said PP has better (quality) overdrive, which can be seen on a scope. SE without FB has more harsh overdrive, with jagged waves on a scope. That was why I wondered if SE could be made the same quality if using FB, or whether it would still be inferior, scope-wise..

[Scumback Speakers]

I've been toying with the idea of building a single ended amp for quite a while, but I've never come across a demo of one that sounded good with distortion. I realise they'll never sound like a Push Pull amp but they just always seem to sound so grating with no definition. The only one that sounded ok was the Marshall SL5, but I suspect that's because it's a Master Volume amp and they're not actually driving the power section. Look at the Vox AC4C1 however and it sounds likes a trebly fizzy mess. Same for the Marshall Class 5, absolutely no definition, just fuzzy mess.

What are your thoughts? Can single ended amps sound good with distortion? Or are they better kept clean.

I've been a fan of single ended amps for 50 years. I updated the old Gibson Gibsonette GA-8 dual 6V6 design in the early 2000's with a few tips from Dumble on how to make it sound better. Here's a couple of clips.

Hideaway, forgive the clams over the backing track.
https://scumbackspeakers.com/scumnicocl ... umnico.mp3

Major Crunch, quad 6V6 with a Les Paul with Jim Wagner DarkBurst pickups.The lyrics are pretty raunchy, you've been warned!
http://www.scumbackspeakers.com/jimtune ... dpussy.mp3

[Colossal]

Major Crunch, quad 6V6 with a Les Paul with Jim Wagner DarkBurst pickups.The lyrics are pretty raunchy, you've been warned!
http://www.scumbackspeakers.com/jimtune ... dpussy.mp3

Crass tone, crass tune. What more can you ask for?

[bepone]

@bepone said PP has better (quality) overdrive, which can be seen on a scope. SE without FB has more harsh overdrive, with jagged waves on a scope. That was why I wondered if SE could be made the same quality if using FB, or whether it would still be inferior, scope-wise..

but SE is A class and clean is maybe better than synthesis of the signal in PP amp, for OD you can use pedals