Help please checking my B+ design

[gary h]

Hi all,

could I get a few of you vets to take a brief look at my PSUD2 sheet. This is for an Aikido linestage B+ supplying 4 6SN7s, using a 5AR4 rectifier and a Hammond 272FX (300-0-300, 146VA, 5V@3A, 6.3V@5A.)

I set a 40mA load taking 10mA plate load from the 6SN7 data sheet.

I found a formula to calculate inductance, I ended up with 7.5H although I'm not sure if that should be total or just the first choke.

I hope I understand correctly from reading on the forum that the first cap will limit turn on/off voltage spikes.

After reading Jim Hagerman's snubber paper, (and understanding too little despite it's clarity,) I tried calculating an RC section but the one I ended up with seemed to get the ripple down from 40mV pp to 1.4mV. I don't know how oscillation will be affected, if the PSUD2 scope is to be a guide, it looked pretty good.

Voltage at I1 is 295V which seems like a good deal.

I'd appreciate hearing concerns, improvements, and other tips that will help, especially in keeping me alive and the Aikido working well. I've decided to follow John Broskie's recommendation to employ a choke based filter although I have read several posters claim that this is an unneccessary expense.

thanks,

gary

[SY]

What you want to do is see what happens when the ps is hit by a transient. Do a current step, maybe 40 to 45 mA and see if the supply settles to the new voltage in a well damped way or whether is sproings around a bit.

[gary h]

Thanks for the reply,

how long should I run the sym for and what pause period?

gary

[Cappy]

Gary,

In line with what Sy is saying -- there is some information in my Aikido thread which discusses what to look for in the impulse response. I tried to make the information useful for others like you.

I'm a power supply design beginner too, but after playing with a real power supply for a while, I've confirmed the impulse approach holds up in real supplies so I recommend it as a good design methodology, at least as a good starting point.

I've modeled your power supply so can follow along with your efforts. Homework question for you if you are game - how does your power supply's impulse response differ from the "ideal", as suggested by the impulse theory?

I have some other comments too on your supply on how to size the inductors and caps, and the optimum number of cells. I made a good improvement to my supply today which may help you, which I'm going to describe when I have more time to write it up tomorrow in my thread.

[Cappy]

Try running for 2000 ms after a reporting delay of 4 seconds. In the step response dialog, set value1 to 40mA, value2 to 36mA, and the time to 5 seconds.

[gary h]

Thanks Cappy,

If I remember correctly didn't you start the YAAB thread? I have intersected it in my searches many times. You are using the TentLabs DC regulator boards, right? I'm glad you fielded this endeavor on the forum, it's nice to see common problems being tackled. That said, much of it is yet over my head. I don't have a PC so I have to climb in through my neighbor's window when he's not home and use his fr PSUD2. I'll try the varied current load simulations. So many advise on the forum to be liberal when specing a transformer. Clearly the one I have in mind can provide 2X the max current consumed by the 6SN7 heaters, and 5X that required by the rectifier tube. My understanding is that this is the most important consideration, (given decent design,) in maintaining consistent voltage and current supply. I look forward to checking in with you soon.

gary

[SY]

It's a tube rectifier, so it's worthwhile to run it longer before the bounce, just to take care of warmup, maybe 15-20 seconds or so. I did a fast sim of the circuit and it looked pretty good.

[zigzagflux]

With regards to your issue of snubbers, I too have read Jim Hagerman's article numerous times, but in practice, have found o-scope/test/trial/error to be the most reliable method. It is also not always practical to calculate (or approximate) C and L values to plug into his equations. If anything, they give you a ballpark of where to start for C values.

I also would say PSUD will probably not help you to identify proper R-C snubbers for reducing transients (reverse recovery, inductive kickback). My process may not be the best method, but it works pretty well for me. I can give some advice in this area if you are interested, but you might be preoccupied at this point with getting good transient response per the above suggestions.

Fortunately, snubber selection is fairly independent of C-L-C-L-C design, so once you establish the filter components, you can proceed into snubber selection.

Good luck. PSUD is a great little tool, and gives surprisingly accurate results.

[gary h]

Thanks SY,

That's what I like to hear, I'll try some more sims and move on to the heater supply.

gary

[gary h]

Zigzagflux,

I would definitely be interested. After my last partially successful preamp build I decided to learn a lot more before rushing into the next one. This means that I will plan as much as I can before ordering all the parts. This is all to say that I won't be able to physically test the circuit for a few weeks but if you think your snubber advice will suffer this abstraction, by all means lay it on me.

thanks,

gary