[HomeBrew] Dual output power supply?

Sat, 14 Feb 2004 22:34:54 GMT

Jim! 
Glad you answered this one! HV choke is a 6-12 Henry "swinger" while the low voltage item is a 6 Henry 150 mA unit. Everything will be solid state rectification. I will probably use some fairly large caps for filtration. I do have a number of 520 uFd/400 VDC caps in stock and I also have access to the 100 uFd/350 or 100uFd/450 vdc caps if needed. 

On the filament side of the house: I don't have to use the onboard filment windings on the plate. In fact, the 6.3 VAC c.t./20 Amp Triad I have can power both the 812A's, the two 6146's, the 807, the 6L6, and a pair of minis with lots of headroom to spare. Or, if it is going to be critical, I can always get another smaller filament xfmr dedicated for just the Millen modulator and transformer. I will probably use, however, the 5.0VAC tap with a reversed 6.3VAC to 120 VAC filament transformer for biasing voltage. I need -45 VDC so I'll probably just half wave rectify and filter the output of that and then use a pot to tap off the -45 VDC spot to bias the transmitter.

Other than that, that's it! Let me know your thoughts. Cal. N6KYR. 

In a message dated 2/14/04 1:33:28 PM Eastern Standard Time, [email protected] writes:

I need help for a power supply I'd like to build. The output I'd like to have will be around 400-600 VDC (about 90-100 mA) for the plate supply and 200-250 VDC (30 mA) for the screen supply. I found a 600 VCT, 250 mA xfmr from Hammond that I have on hand. The prospective circuit would be to use a full wave bridge the two outer windings and run it through a pi networked choke/2-cap filter. The center tap will not be grounded but instead, run through another choke and filter cap. I saw a similar circuit on building up a vintage transmitter. Does anyone have any design considerations or comments about doing this type of circuit? 

What you describe is known as the "economy" power supply. Goes back more than 50 years. 

The main concern in your application is the output voltages. If the transformer delivers 600 VAC to the bridge rectifier, the output voltages will be as high as 840 VDC on the high tap and 420 VDC on the low tap if a capacitor input filter is used (you get the peak voltage if the input capacitor is big enough) . If you use choke-input filters and the input choke has at least critical inductance, the output voltages will be as high as 540 VDC and 270 VDC. 

So you can see that the filter design requires a bit of consideration...

What sort of rectifiers will be used, and is the load steady or varying?

Will the transformer be used for heater windings as well, or just B+?

73 de Jim, N2EY

(who just brought a nice pair of 866As out of remote storage...) 

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