[ARC5] [Milsurplus] Troubleshooting Tips from the Late Nick Broline, #2

[Robert P. Meadows]

Folks,
I do believe that Tom Frobase has already solved what you are working on.
He has developed the "solid state dynamotor" for ARC 5 radios.  The units
are available from his website which I believe is KitParts.
Do a look about it my memory is fuzzzzy.
Tom also has the slick capacitor kits that replace the beeswax filled paper
capacitor tubs on the ARC 5.  Whilst the underchassis will have more space
and not look original, the radios work fine, and, having done several, will
never try to open and restuff the cans.  The only proper method of opening
the cans it to lift the sealing lip in a special jig, get the goo out,
replace the capacitors and then reseal in the manner in which the cans were
originally built.  Gluing them together is just a nasty little trick that
will not last, and on any close inspection will reveal the "..rigged"
solution.  
Were ARC 5/ARA/BC radios still in use, when sent to Depot Repair, the Depot
would have surely advanced to a method much as Frobase has developed.  


Cheers,
Robert
W4RRD

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
<milsurplus-bounces at mailman.qth.net> On Behalf Of David Stinson
Sent: Sunday, July 9, 2023 1:25 PM
To: ARC-5 <arc5 at mailman.qth.net>; milsurplus at mailman
<milsurplus at mailman.qth.net>
Subject: [Milsurplus] Troubleshooting Tips from the Late Nick Broline, #2

Back in 2021, Nick and I were experimenting with those little yellow
"0-400VDC" power supplies you see on Amazon and Ebay.
There has been some recent discussion concerning them, so those with an
interest might find Nick's preliminary tests interesting.
----------------------------------

I had ordered 4 of the yellow colored 45-395V boost converters a year ago,
then promptly misplaced them. Took three days to find!
(Lord, I know that feeling. DS)

I put the supply feeding a 20W wire-wound w 3.5K load. Ran it off a 13.5 VDC
fixed output enclosed Lambda enclosed supply.

That looks like the following:

@180V Io = 51ma. W = 9.25W

@220V Io = 63ma W = 13.8W

@250V Io = 71 ma W = 17.9W

What I found was that the 180V performance was bulletproof into the R load.
It the switcher could start with that resistive load, and was happy
connecting the load and re-applying it while running. This would be perfect
for an ARC-5 or ARC-12 receiver under all circumstances.
The 220 output was about the same.

The 250V output handled the load well, but when I tried to start the supply
from the 12V source and the switcher loaded it would ramp up to ~180V and
stop. Disconnecting the load, then reapplying it, would let the supply
recover to 250V output. This told me the supply would run a receiver well,
but it you interrupted the source with the filament hot (and operating on
12V), the supply wouldn't come up all the way.
Switching to a higher input voltage, like 24V, seemed to work perfectly.

The switcher IC is a TI UC3843A which is a controller that charges an
inductor until the current reaches a value specified by the voltage sense
circuit. It make a current measurement every cycle. What I'm thinking is
that when starting under load the chip runs into its current limit on each
cycle and can't deliver any more energy into the inductor (and load, of
course), and the control loop can't coax any more output. 
Looks like the converter gets "stuck." I don't know if anything is getting
hot in the supply.

I suppose this says if I want to use the converter at a higher output
voltage and current, but still within its limits, it has to be with a higher
source voltage to get it to start under load, or needs to always start
working into a low current load.

Next time I get back to the bench I'm going to look at the converter with a
scope and see if its bumping into another "chip" limitation.

I also noted that the output of the supply overshoots when the 71ma load is
removed, and I think that's because they are using a very large output cap
(100 ufd, I think) for the application. I seem to recall the normal output
cap is a large ceramic, like maybe 2uFd.??????  memory again.....but its
been ~25 years since i dealt with these things.

73
Nick Broline


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