First, I have a much bigger trash can at my house, so you can send that supply
my way ! No sense wasting it in YOUR trash can.
Second, if the supply output voltage did change as a function of load, then the
723 regulator is not doing its job. I can tell you that the whole idea of a
regulated power supply is to maintain the output voltage regardless of load, at
least until something draws excessive current. I set all of my supplies to
14.00VDC and label them as such; haven't had a problem in 20 years. The crowbar
shouldn't fire until about 16 volts, but it certainly IS sensitive to RF, and
if a lot is floating around, that can definitely trigger it. Whether it's the
SCR itself, or the sense circuit driving it, something is causing it to fire
and blow the fuse. You'd need to measure the actual output voltage of the
supply to see if it's going that high or if the SCR is being falsely triggered.
Of course, you only get one shot at trying it before the fuse blows.
Astron supplies will not turn on if there's a significant load on them when AC
power is applied. I had one powering a 90w amplifier that drew about 16 amps.
If drive was applied when I turned the Astron supply on, it would output zero
volts. I had to remove the drive, thus removing the load, then turn the supply
on, then turn the drive on. Most of the time this isn't a problem. It does the
same thing with a 1/2 ohm load attached to the output terminals; goes into
immediate current overload foldback. Seems to be happy to sit that way, but of
course you don't get any output voltage.
Bob M.
======
--- On Mon, 12/22/08, n9wys <n9...@ameritech.net> wrote:
From: n9wys <n9...@ameritech.net>
Subject: RE: [Repeater-Builder] Astron P/S question
To: Repeater-Builder@yahoogroups.com
Date: Monday, December 22, 2008, 1:17 PM
Since I’m the one who started this thread, I think it is incumbent upon me to
let the collective masses know how I am proceeding…
To date, I have added additional filter caps (0.1 µf disc caps) to the SCR
(GATE to GND) and across the output of the supply. I have already affixed
ferrites to both ends of the cabling going from the supply to the PA. I am
still blowing fuses. I am planning on adding caps from each output line (POS
and NEG) to chassis ground.
I was also told to dial down the output voltage a bit (it is at 13.8V now) to
around 13.2V, because the Astron “ramps up” the voltage to its transistors as
the supply nears rated capacity, which closes the gap between the operating
voltages and where the SCR triggers. Can anyone confirm this? In the end if
these fixes fail, I will be relegating the Astron to other duties (AKA: the
trash can).
I temporarily replaced the Astron supply with a 75A switching supply, and so
far no problems – even after 30 minutes of steady operation of the repeater.
(The Astron would fail after about 10 – 15 minutes of operation.) I was able
to get my hands on a service monitor – the building is not shielded in any way,
so there is RF all over the place. The only major peak we saw, however, was
about 11.7 MHZ down from the center freq of my UHF repeater (the repeater TX is
at 444.5500, the bump was at 437.8500) and after some testing we found it was
from the switcher. It does not seem to be affecting the receiver of my
repeater…
For now, I think I’m going to stay with the switcher, until I am sure we have
found a permanent fix for the Astron. Besides, with the current temp at -2°F,
I’m in no hurry to go to the tower site. <grin>
How ‘bout it, Skipp?? Any ideas? I know you’ve been away and busy, but I hope
you are catching up on the thread…
Mark - N9WYS
