[ARC5] Building a power supply for an ARC setup

Mon Apr 22 17:54:35 EDT 2013

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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