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Old 12th November 2019, 01:04 AM   #1
soundwavesteve is offline soundwavesteve  United States
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Default Is this above my skill level?

Hello all,


I am starting a build of the BA-3 as a preamp and am working on the power supply part of the design. I am following 6L6's build guide and was going to add the SuperReg board to the build when I realized I am in over my head lol.



The BA-3 Preamp guide is using a discontinued Glassware power supply/regulator combo unit. In the guide he recommends the Superreg as a replacement, so that is what I bought. I didn't realize until after I bought it that the regulator is just that, and it still needs a rectifier and PS filters before it. I thought there must be a simple pre-made design/PCB that would include the rectifier and filters and I could just add that and be on my way. While there are a few, most of them come from China and take a month or more to get here by mail. So scratch that. I know the store here has a PS board with a diode board but I am hesitant because of what I read in the next paragraph below.



So I started reading the Linear Audio papers and thought I could build something quick myself; well that is way over my head. I do not have the tools or the knowledge to continue with those concepts. What I did take away from the Linear Audio papers, specifically Part 4, is that he recommends a CLC network before the rectifiers, snubbers around the rectifier and an LC after each rectifier with a bypass cap. Well there is no pre-made PCB board that has all of that, which means I have to make my own on perfboard. Further research suggests that I shouldn't attempt this unless I have an oscilloscope, which I don't, as I could do more harm than good with the wrong values.



So, the question is, can I use the values from the Linear Audio article and keep the superreg or is this beyond my skill level and I should just get the current Glassware bi-polar 24v power supply/regulator. Is the BA-3 preamp so good that it would noticeably benefit from the best/most sophisticated power supply I can build? (assuming one had the amp/speakers/wires/etc of the same quality).



For reference the article has the mains line CLC as .47uF/250AC - 56mH choke- .47uF/250AC.
The snubbers are all .47uF. The LC (per rail) is another 56mH choke - 2200uF/35v with .47uF bypass.



Hope you have a great day!
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Old 12th November 2019, 01:25 AM   #2
rayma is offline rayma  United States
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It will work with any bipolar power supply of the right voltage with enough current (just over 100mA). Better power supplies (the definition is not important right now) could sound better and have lower noise. But you can start with the audio board and a lab supply, or any other convenient one. You can always change the supply later on. I would suggest getting a basic bipolar lab supply, preferably with current limiting, which you could use for both testing and operation, and also for other work later on. You'll need it.

Last edited by rayma; 12th November 2019 at 01:34 AM.
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Old 12th November 2019, 01:35 AM   #3
soundwavesteve is offline soundwavesteve  United States
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I was thinking about using the Glassware supply now and coming back to the superreg later, but if I am just a nudge away from understanding/building the more sophisticated supply, then I would rather spend the money on that. You are right of course, can always use the bipolar supply on another project or test bench if I ever go that far with this addictive hobby ;-P
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Old 12th November 2019, 04:02 PM   #4
indianajo is offline indianajo  United States
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I built mine on NEMA CE board from mcmaster. Drilled my own holes. Use euro terminal strips for wires in/out, screw these to board with 3 mm or #2-56 screws & elastic stop nuts. Screws also mcmaster, euro strips from newark digikey mouser.
Find a transformer. I used a wall transformer but you wont find that in tube voltages. Install 2 bridge rectifiers from ends to CT. Filter resultant with 2 electrolytic caps, I used 1000 uf for 6 op amps.
If you put a 160v to 330 v rated MOS supressor across the input the transformer and after the fuse, it can reduce lightning pops. Also maybe save the transformer some day. I lost a PAS2 power switch to lightning, also turn off pop supression capacitor vaporized.
If you put a .01 uf 1000 v rated disk cap across the rectifiers, can reduce shutoff noise from the SS diodes. With the MOS supressor disk cap can be 500 v rated, lightning surges aren't so vicious. Everybody used 1000 v in the 50's 60's 70's before MOS supressors.
If you still have hum, add a 1 ohm after each filter cap, after that put in a second filter cap each side. That's a pi filter. At low currents of a tube supply, maybe 22 ohm resistors.
Fits on a 1.5"x3" board in my RA-88a mixer, on #6 screws with 3/4" of 1/4 air tubing for standoffs.
If only need one supply, not +- supply for op amps, forget the center tap and use one of everything, not two.
BTW put transformer in its own steel box away from the high gain RIAA circuit. Dynaco did, Peavey does. Flux emissions can hum. Both wrap the transformer in steel jacket, but you can only buy those in dead equipment. Junk Peavey mixers are $25-$75, have everything you need for +-16v . Listening to a Peavey MMA-875t right now, $70, had two bad solder joints from factory. Practically unused since 199?.
Junk dynacos are $$$. Dynacodoctor or somebody might have wrapped PAS3 clone transformers, will feed 4 12AX4's.
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Last edited by indianajo; 12th November 2019 at 04:17 PM.
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Old 13th November 2019, 03:12 PM   #5
soundwavesteve is offline soundwavesteve  United States
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Thanks for the info! Your suggestions are very similar to filter cap and rectifier cap values I have seen elsewhere and should be just fine for this circuit as well. Is the second cap after the resister in the pi filter the same value as the first one?
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Old 13th November 2019, 04:27 PM   #6
indianajo is offline indianajo  United States
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Can be same value, can be bigger or smaller. I used 1000 uf for my op amp mixer, a 48 ma supply. The one filter cap got hum down to about -50 db. Resistor & 2nd filter cap got it down where I can't hear it.
Vacuum tube filter caps are usually 33 or 47 uf, biggest value a 5AR4 rectifier will do without arcing. SS rectifiers don't have the problem with arcing. They do start up hard and possibly hammer your cathodes cold, some say. A NTCR in series with the transformer primary stops that hard start. I use the GE cl-90 or some such for small loads. I put NTCR & MOS supressor on solder eyelet terminal strips. Formerly sold by cinch, now imported. Screw these terminal strips to case or rectifier board with #6 screws and elastic stop nuts. You do have a #1 to 80 drill set don't you? Mine has stamped in the holders the value of drill you need to clear #6 & # 2 screws, also all the other ones. BTW harbor freight drills are garbage. Mcmaster or grainger is best source. I don't like grainger because they will send 3 boxes from 3 warehouses for 3 items, $32 in freight sometimes. Mcmaster only has 2 warehouses and most times they get all short things in one $7 box.
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Last edited by indianajo; 13th November 2019 at 04:31 PM.
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Old 13th November 2019, 05:27 PM   #7
randytsuch is offline randytsuch
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Is this above my skill level?
You might want to get and try duncan amp tools psud II (power supply designer).

It lets you specify a simple front end of a power supply, and shows you the output V as a graph, or any other V or I in the circuit. It also lets you add filter stages (C, LR or RC) so you can see impact of each stage.

Pretty useful if you want to start building simple, unregulated power supplies.

Also I've built a lot of circuits with just a meter. Its nice to have a scope, but not required, imho.
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Old 17th November 2019, 12:12 AM   #8
soundwavesteve is offline soundwavesteve  United States
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Thanks for everyone's help! I decided to use Tubecad's bi-polar regulator supply for now while I learn more about power supply design and experiment with the PSU Designer. Just briefly playing with PSU designer showed me how minor miscalculations can cause more problems, definitely want to avoid that until I have a better understanding of how things interact.
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