schematic question? 805 feedback

[scutterflux]

OK, I was wrong about the TF phase thought it would be like on schematics but mine is not, ie; positive feedback is edgy...anyway I got to try out Cathode FB after a bit of soldering and it did tighten up bass a little but the sacrafice of everything else is defintily not worth it, it was appearant right away, similar to GNFB but not to smear as much. I'm finding SET bass to be kinda relaxing, it's still large and defined but just doesn't have great impact.

BTW 4ohm tap did sound better.

Thanks for the help so far.

[puremilk]

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[H.Michi]

Originally Posted by scutterflux

OK, I was wrong about the TF phase thought it would be like on schematics but mine is not, ie; positive feedback is edgy...anyway I got to try out Cathode FB after a bit of soldering and it did tighten up bass a little but the sacrafice of everything else is defintily not worth it, it was appearant right away, similar to GNFB but not to smear as much. I'm finding SET bass to be kinda relaxing, it's still large and defined but just doesn't have great impact.

BTW 4ohm tap did sound better.

Thanks for the help so far.

Amount of cathode feedback depends on Mu of output tube and turns of 2nd or 3rd winding coils of OPT.
In my opinion, dumping factor of tube amp should be 1.0 at least.
My OPT has 36 ohm of 3rd winding coil which adapted to 838(Mu of 50) and gets dumping factor of 1.6 with only CFB.
If you don`t want using GNFB, you should use full of your 2nd winding, 16 ohm tap. May be you can get nearly 1.o of DF?
I learned that even CFB with OPT, too much amount of NFB is affects to the sound (too tight).
I have tried attached cathode feedback on my 811A SE amp.
An 811A has so high Mu(160) that 36 ohm of 3rd winding seems too much.
With out CFB, dumping factor was 0.2 and with 36 ohm of CFB DF become 2.0.
Schematic 14 shows added 50 ohm of resister in between cathode and 3rd winding coil, functioning current feedback and reduced
dumping factor from 2.0 to 1.5.
Schematic 15 shows using 4 ohm of 2nd winding coil and added
small amount of GNFB and get total DF of 1.0.