• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

SE with the KR300BXL from KR Enterprice

Ralph,
the KR300BXL is the best 300B avaiable IMO. It rather sonds like 45 than like a 300B while having much power.

The amp schematics look reasonable to me. Just one objection: this is a single ended amp which is no constant load for its PS.
A CLCLC filter for B+ certainly has a good static filter effect but on load changes it shows a step response taking eternally for coming to rest.

Suggestion: download PSUD II and simulate your power supply. You will see that a simple LC or CLC filter responds much friendler on load changes.
 
Hi Bernhard,

Thanks for your comments. I'm aware of the fact that the PSU has some problems, I've simulated it in PSU designer. I was in the first place very interessted in the comments about the amplifier schematic itself. Seems a bit complicated, and I've found another schematic today http://www.audiodesignguide.com/my/300blxs_amp_sch2.gif

What do you think?

Ralph
 
Ralph,
this second one would rather be my choice. Although methinks with a 6SL7 a SS constant current source will work better than a plate choke. The 6SL7 has a plate resistance too high; the choke's inductivity might be too low to give you a proper lower bandwidth limit.

I would replace the Jensen coupling caps by SiemensEpcos MKV 25839. By any means! And for the 6SL7, i would try to get my hands on a vintage redbase RCA 5691 or vintage metal base Sylvania 6SL7.