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Power supply circuits

9/2/1997 3:28 PM
Power supply circuits
okay here's another ignorant question. Although if I weren't ignorant, why would I ask? Looking in my Hammond catalog I see a power transformer that puts out 350-0-350 AC volts RMS. If this is the case and I use a choke filtered full-wave bridge rectifier, their equation shows that my peak and average output in volts D.C. will be .9 times the secondary volts A.C. I am assuming that in this case I will get 700 volts from a full-wave circuit and 350 volts from a half wave circuit so my output will be 630 volts D.C. but since I'm still learning and I have no good reference to check I'm asking one of those with more knowledge than myself. Am I right?
9/2/1997 10:21 PM

Don't use a half wave either..........  
You should just use a full wave rectifier.  
That way you ground the center tap...350VAC 0 350VAC and the rectifiers will see only the 350VAC from each leg of the secondary relative to the grounded center tap.  
Now you will have 350VAC: times 1.13 for a 5Y3 or  
times 1.3 for a 5AR4, or times 1.41 for a pair of solid state silicone diodes.  
Now be carefull cause the different rectifiers require a different heater current.  
5AR4 in this power supply will draw about 2 amps at 5 volts AC and be about  
1.3 x 350VAC = 455V DC unloaded on the B+ supply rail.  
It will be less then that once you get the tubes in and they start drawing resting current.  
I would expect to see about 410V DC to 420V DC... or less if you are building a Class A final amp.  
Hope this helps a little.  
9/3/1997 9:19 AM

Now I understand what the results will be if I use a full wave rectifier, but why shouldn't I use a full wave bridge. Is there some detriment that I am not aware of (obviously). Also, regarding the heater current, I like the idea of using separate transformers for plate supply, 5v heater supply, and 6.3v heater supply. Is there any negative effect using separate transformers? I know I've seen this type of setup on audiophile amps.
9/3/1997 9:38 AM
J Fletcher
350-0-350 assuming you're using the 2 outside windings gives you 700v AC,into a bridge rectifier would result in about 875 volts DC.

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