[ARC5] Building a power supply for an ARC setup

[John Hutchins]

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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