May 22nd, 2018, 11:28 pm
May 23rd, 2018, 7:05 pm
May 24th, 2018, 9:46 am
May 24th, 2018, 9:53 am
justinis wrote:Thanks, Roscoe. The LR8 datasheet I was looking at had a 0.5mA min output current so I think that will be ok.
justinis wrote:This is the first I've heard about regulating B+ and the screens, not just the screens. I've had a lot of people recommend regulating the screens to me, but no one has mentioned regulating B+ (which I believe refers to the plate voltage, right?). Is there no advantage to regulating just the screens? Regulating both would be a pretty big change to my amp and I'm not sure I'm up for that. Should I just leave it the way it is? Here is the full schematic: https://www.dropbox.com/s/qe1a8vvzyq7x1d0/ST-70%20clone%20schematic.pdf?dl=0. I was planning on replacing the box that says "regulated screens option" with the circuit above.
May 24th, 2018, 10:22 am
May 24th, 2018, 11:36 am
Roscoe Primrose wrote:justinis wrote:Thanks, Roscoe. The LR8 datasheet I was looking at had a 0.5mA min output current so I think that will be ok.
Oops. With the 407K R1 it'll be just less than 0.8mA, so you may still want to add more load.... Either a smaller R1 (and adjusted R3 to get the voltage where you want it) or a 100K resistor in parallel with C2 ought to do the job. Keep in mind that 100K at 325V is just over 1W.justinis wrote:This is the first I've heard about regulating B+ and the screens, not just the screens. I've had a lot of people recommend regulating the screens to me, but no one has mentioned regulating B+ (which I believe refers to the plate voltage, right?). Is there no advantage to regulating just the screens? Regulating both would be a pretty big change to my amp and I'm not sure I'm up for that. Should I just leave it the way it is? Here is the full schematic: https://www.dropbox.com/s/qe1a8vvzyq7x1d0/ST-70%20clone%20schematic.pdf?dl=0. I was planning on replacing the box that says "regulated screens option" with the circuit above.
If you only regulate one, then the difference between B+ and screen voltage changes with line voltage. I'll let one of the guys who routinely builds with pentodes comment further...
Roscoe
May 24th, 2018, 1:51 pm
May 24th, 2018, 3:55 pm
May 24th, 2018, 4:06 pm
May 24th, 2018, 4:14 pm
justinis wrote:Oh yes I understood what you meant, I was just hoping Roscoe would chime in as to whether he agreed with your analysis. Makes perfect sense to me but I am no expert on these things (which is why I come here!). But it sounds like you have it on good authority and evidence, so that should be good enough for me.
Out of curiosity, do you think there's a sonic advantage to regulating everything (B+, G2, bias)?