[ARC5] Building a power supply for an ARC setup

Mon Apr 22 20:33:14 EDT 2013

And if you need one of those, I can supply one.
Ray Chase

----- Original Message ----- 
From: "Bob Macklin" <macklinbob at gmail.com>
To: "John Hutchins" <jphutch60bj at gmail.com>; <arc5 at mailman.qth.net>
Sent: Monday, April 22, 2013 5:54 PM
Subject: Re: [ARC5] Building a power supply for an ARC setup

>A suitable powersupply can be made by using a 120/240V isolation 
>transformer.
>
> Connect it as in a Heathkit voltage doubler supply.
>
> 240 * 2 = 480V.
> 480 * 1.4 = 672VDC
>
> That's plenty for an ARC-5 transmitter.
>
> Bob Macklin
> K5MYJ
> Seattle, Wa.
> "Real Radios Glow In The Dark"
> ----- Original Message ----- 
> From: "John Hutchins" <jphutch60bj at gmail.com>
> To: <arc5 at mailman.qth.net>
> Sent: Monday, April 22, 2013 2:42 PM
> Subject: Re: [ARC5] Building a power supply for an ARC setup
>
>
>> All -
>> Take the regulator circuit on duncan amps and modify it for 750V , I am 
>> modifying the same circuit for adjustable voltage, ~220vDC. It is a 
>> comparator.  The sims show very flat DC output, for less weight and 
>> possible cost savings.   What is the cost of a 10Hry 100ma choke these 
>> days? It could be free if you have it in your junk box, I agree.
>> Just a suggestion
>> Hutch
>> On 4/22/2013 6:54 AM, Brian Clarke wrote:
>>> Hello Fred,
>>>
>>> The BC-696 was designed for screen modulation. This means that the 
>>> maximum Voltage on the plates is usually your dc supply. The RCA 
>>> Transmitting tube manual says that the 1625 as an RF PA tube can stand 
>>> 750 Vdc plate Voltage in Class AB2 ICAS service, which is pretty close 
>>> to what the design is. While a choke input filter would give a better 
>>> quality output, 900 x 0.9 = 810 Vdc is a bit too high. If you can 
>>> parallel the two secondary halves and bridge rectify into a capacitor 
>>> input filter, 636 Vdc is very likely, a little lower if you run into a 
>>> pi filter. You would get essentially the same output Voltages if you use 
>>> full-wave rectification into a capacitor input or pi filter. The problem 
>>> with capacitor input or pi filtering is the higher output Voltage load 
>>> regulation compared with choke input. The Duncan  Amps suggestion of 528 
>>> Vdc seems a bit low, unless there is a very heavy bleed in a child-like 
>>> attempt to reduce load regulation of the output. If the secondary dc 
>>> resistance of each winding is 16 Ohm, at maximum current drain the 
>>> Voltage droop should be 5.7 V, not the 108 V the Duncan Amps design 
>>> suggests. Even if the choke were 100 Ohm, the additional Volt drop at 
>>> full load would be 36 V. I am assuming you would use solid-state 
>>> rectification; if you used tube rectifiers, you might get up to 100 V 
>>> drop. This high Voltage drop using hollow-state rectifiers makes the 
>>> output load regulation much higher (worse).
>>>
>>> The main thing limiting the VA rating of the transformer is likely to be 
>>> the core. You don't get more current from FWB rectifying two parallel 
>>> windings compared with FWCT. The heating of the windings will be the 
>>> same. In FWB, both windings heat at the same time; in FWCT, the windings 
>>> heat on each half cycle alternately - so, the average heating is exactly 
>>> the same, as is the average output current.
>>>
>>> I would suggest a 10 H choke if you can. And if you are worried about 
>>> its insulation after years of solitary shelf life, put it in the 
>>> negative lead. In that position, you can use it to provide a bit of 
>>> negative bias, if you need it. Bear in mind that the bias will vary with 
>>> load current.
>>>
>>> 73 de Brian, VK2GCE.
>>>
>>> On Monday, April 22, 2013 12:37 PM, you said:
>>>
>>>
>>>> I have been hunting around for a HV transformer for a power
>>>> supply specifically for a BC-696 (and a future series modulator) - and 
>>>> last
>>>> year happened on what looks like a half finished power supply 
>>>> consisting of
>>>> a Freed RPG-26 at a local hamfest.
>>>>
>>>> According to the specs this transformer can deliver 900v at 320 va. 
>>>> Yikes -
>>>> a bit TOO much voltage.
>>>>
>>>> However, this transformer has a nice feature in that the secondary is
>>>> actually TWO separate secondaries - each one (I'm guessing) delivering 
>>>> 450v
>>>> on an 16 ohm coil.
>>>>
>>>> My question is:   Can I parallel the secondaries for 450V ac with more
>>>> current?
>>>>
>>>> According Duncan Amps PSU Designer- that would give me around 528 volts 
>>>> DC
>>>> IF I  can find a 5hy Inductor that will withstand the current load.
>>>>
>>>> Am I barking up the wrong tree?  I need an OT to straighten me out 
>>>> then....
>>>>
>>>> Thanks for all your help in advance.
>>>>
>>>> Fred Cousins
>>>>
>>>> KD7EDW
>>>
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>>
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>
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