[ARC5] 28 volt transformer question ?

[J Mcvey]

 It's very true that the "junk" available in the  60's wasn't very conducive to running a 28V rig.I remember that nothing that I could find in the dump would come close to the voltage and current requirements to fire up a dynamotor.  I suppose modifying a couple of beefy battery chargers might have worked, but you didn't find any of those in the dump!
You need a serious supply to start a ARC-5 transmitter dynamotor while running all the other stuff!
I have an old industrial 40 amp SMPS I needed to add a bank of caps to  in order to keep it from going into OC shutdown when keying the transmitter while the whole setup was running.
    On Monday, September 7, 2020, 1:07:15 PM EDT, Robert Eleazer <releazer at earthlink.net> wrote:  
 
  I have a ARC-116 220-400 MHZ AM transceiver I bought onebay years ago and a ARC-114 FM 30-75 MHZ transceiver I got for free.  Ijust knew I could build a 28 VDC power supply for them with stuff I justhad laying around. My first attempt used a 26CT V transformer I bought fromFair Radio in 1974.  Turned out that it was more like 31 VCT with 122VACinput.  I ran though several three terminal regulators before figuringout that it was never going to work; the input voltage to the regulator was toohigh.  I finally built a regulator circuit featuring a passtransistor and that worked if I used a Variac to drop the inputvoltage.  Then I removed the transformer and installed an XL connectorand hooked in a much bigger electric wheelchair charger a neightborgave me.  It worked then.  I added a mike premap using one of the kitsthat Fair Radio sells.  It was a rather awkward package,though. Then I found a discarded stereo amp and built anotherpower supply on a Lear aircraft radio power supply chassis.  After usingsome of the transformer extra secondaries as reverse buckers, putting in a regulator IC, adding a really big pass transistor and heatsink salvagedfrom the stereo, adding a fan, and then built a copy of the mikepreamp circuit; it worked fine, too.  Handles 3 amps 28 VDC outputwithout breathing hard. But it ain't easy to turn commonlyavailable parts into 28 VDC power supplies, even given cheap IC regulatorsfor $1.00 and really high output pass transistors and transformers available intrashpiles by the road.  I do not wonder at all why the guys in the 40'sthrough the 80's did not try to run the gear on 28 VDC; they did not even havethe junk we can get now.
WayneWB5WSV              

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