I suspect you will end up with slightly excessive voltage on the heater string because the DPC-120-200 is specified for 115V on the primary and you're under-loading it by 25%. Your actual line voltage is probably near 120V, so I predict you'll be about 5~6% high. If I'm right, you'll want that 56R resistor.
You're still overloading T1. I know it's counter-intuitive, but secondary winding AC current greatly exceeds DC load current in capacitor-input rectifier circuits. Stancor gives a 'form factor' of 2.3 for HW rectifiers with capacitor-input filters in their transformer literature, which puts effective secondary winding current at 110mA * 2.3 = 253mA. See page 2 of this doc at Stancor's website.
You could switch to a full-wave rectifier, but you end up with zero design margin. Another zero-margin dodge: Parallel the secondaries, making the extra load capacity of T2 available to the rectifier. A better way around this problem is to use a choke-input filter, because you apparently don't want anything near 160VDC from this PSU, but chokes aren't cheap. Not new ones, anyway. Could you hack something?
You're still overloading T1. I know it's counter-intuitive, but secondary winding AC current greatly exceeds DC load current in capacitor-input rectifier circuits. Stancor gives a 'form factor' of 2.3 for HW rectifiers with capacitor-input filters in their transformer literature, which puts effective secondary winding current at 110mA * 2.3 = 253mA. See page 2 of this doc at Stancor's website.
You could switch to a full-wave rectifier, but you end up with zero design margin. Another zero-margin dodge: Parallel the secondaries, making the extra load capacity of T2 available to the rectifier. A better way around this problem is to use a choke-input filter, because you apparently don't want anything near 160VDC from this PSU, but chokes aren't cheap. Not new ones, anyway. Could you hack something?
Thank you, I'm learning a lot from you!
Yes, chokes I got. I take apart a lot of old stuff nobody wants. I have an eico 4 henry choke, 168 ohm. Don't know the amp rating but it looks fairly stout.
Great! Be aware that chokes cease to function as intended when load current is too low or too high. Suggest you simulate.
Will do, thank you. Choke load, not simply in place of one of the power resistors, yes?
I spent some time fooling around with PSUD, and I'm finding that this PSU problem isn't so easy to resolve. A 4H choke-input filter drops DC voltage way too much. I get close to the target (assuming you want 120VDC) with a 1H choke if I add 6.9uF on the input side, but that calls for film caps (4.7uF + 2.2uF) and it only gets xfmr secondary current down to 189mA RMS. Here's that result.
I can get xfmr current down to the same place with an 82-ohm R-input filter. Ripple is about 3X greater at the first cap. Regulation is a bit worse too, but that's not a big issue with class-A power amplifiers. What IS really critical for single-ended amps without feedback is power supply ripple. By using 470uF caps and a second R/C filter of 100R, ripple falls to 33mVpp at the 120VDC output of the second stage. See here.
189mA is uncomfortably close to the xfmr spec. You might settle for this if it's a one-off project and you're sure that plenty of air circulation will always be available. Perhaps someone else has a bright idea...
I can get xfmr current down to the same place with an 82-ohm R-input filter. Ripple is about 3X greater at the first cap. Regulation is a bit worse too, but that's not a big issue with class-A power amplifiers. What IS really critical for single-ended amps without feedback is power supply ripple. By using 470uF caps and a second R/C filter of 100R, ripple falls to 33mVpp at the 120VDC output of the second stage. See here.
189mA is uncomfortably close to the xfmr spec. You might settle for this if it's a one-off project and you're sure that plenty of air circulation will always be available. Perhaps someone else has a bright idea...
I'm glad you posted this! I also played around with PSUD and had the same experience using that choke.
However, good news I think. I was searching my stash of transformers and came up with a brand new Triad F8-120. 120 vct @850 ma. That should fix my power issues, eh? Of course it would have to handle both heaters and B+.
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