DeathRex wrote:I have a 6P3S and GU-50 SE amps. Wanted something bigger.
I've been looking at 811, 845, 813, 814 and 828.
Wondering how well this 838 works at 673 volts?
Schematic looks doable, but 838s are kinda expensive, at least compared to 811s.
Michimori wrote: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.
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.
DeathRex wrote:Wow I totally missed that being feedback.
As the British would say "Brilliant!"
I'd like to use those 600V motor run capacitors, but I'd still need two.
Users browsing this forum: No registered users and 51 guests