[HomeBrew] Re: HomeBrew digest, Vol 4 #121 - 5 msgs

Thu, 19 Feb 2004 04:12:36 -0800 (PST)

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> Today's Topics:
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>    1. Dual output power supply? ([email protected])
>    2. Re: Dual output power supply? ([email protected])
>    3. Re: Dual output power supply?
> ([email protected])
>    4. Re: Dual output power supply? ([email protected])
>    5. Re: Dual output power supply?
> ([email protected])
> 
> --__--__--
> 
> Message: 1
> Date: Sat, 14 Feb 2004 18:31:12 GMT
> To: [email protected]
> From: [email protected]
> Subject: [HomeBrew] Dual output power supply?
> 
> 
> Hi All:
> 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? Thanks. Cal, N6KYR. 
> 
>
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> 
> Message: 2
> From: [email protected]
> Date: Sat, 14 Feb 2004 16:55:07 EST
> Subject: Re: [HomeBrew] Dual output power supply?
> To: [email protected]
> Cc: [email protected]
> 
> 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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> 
> Message: 3
> Date: Sat, 14 Feb 2004 22:34:54 GMT
> To: [email protected]
> Cc: [email protected]
> Subject: Re: [HomeBrew] Dual output power supply?
> From: [email protected]
> 
> 
> 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? 
> 
> 
> 
=== message truncated ===
Cal,
 It sounds like your filament xfmr. is oversized-20
amps? I believe that 812's require appx. 3 or 4 amps.,
each. Be careful about the surge current, upon initial
power application. Otherwise, you may shorten the life
of those 812's.
              GL & 73 de Ron n4gjv

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