Jim,
My experience with Astron linear supplies has been along the same lines as
others who have replied. In general, very low failure rates, at least for
the RS-20 series. I know of one that still works fine after 25+ years,
and I have another that is more than 15 years old. Several friends have
them, also no problems. The 723 failures you've seen could be due to
changes that were made by manufacturing that were not necessarily approved
by engineering (I"ve seen that happen with many companies!). Another
common cause of problems is when an input side by-pass cap is omitted (in
the name of cost, of course). Most regulators will work OK without one,
but ... it has been known that as the chips age, characteristics can
change and what once was OK is now an oscillator (really nasty conducted
RFI!) or simply toast.
You make a good point about the result of a shorted regulator unit being
full unregulated voltage output. That gets applied to whatever is
connected to the power supply and can surely damage some rigs, if not
most. I have installed 15V Transzorbs (TM) across the DC power inputs of
any rigs I have that don't have reverse polarity or over-volt protection.
I make certain, of course, that there is a fuse ahead of the Transzorb.
Note that the Transzorb acts as a "regular" diode in the event of a
reverse polarity connection and conducts heavily to ground, so I get two
protective actions from a single device. MOVs could also be used, but
they won't provide reverse polarity protection.
73, Dale
WA9ENA
"Jim P" <jvpoll@dallas.net>
05/26/2007 07:11 PM
To
<rrath@charter.net>, <dgsvetan@rockwellcollins.com>
cc
<rfi@contesting.com>
Subject
Re: [RFI] RFI from Astron power supply
I have to beg to differ that this series of Astrons (the
linears like the RS-35M et al) are all that 'reliable'.
I have had to replace the LM723 (I think it is) regulator
on a couple of these and have since made a circuit
change (added a resistor) to give the regulator a better
chance at life.
The 'symptom' of failure was the inability to deliver rated
current without voltage 'sag'.
It is also a good idea to add an LED (with suitable series
resistor) across the unregulated DC side of the transformer
and make this visible/viewable through one of the slots on
the top of the supply towards the rear.
This does two things: you will know when you 'lose' the
regulator side of the PS but know you have unreg DC and
this also provides a bleed-off path. My recollection is that
there isn't a suitable bleed-off on that series (maybe the
earlier ones anyway which may be what I have.)
Jim P // WB5WPA //
----- Original Message -----
From: <dgsvetan@rockwellcollins.com>
To: <rrath@charter.net>
Cc: <rfi@contesting.com>
Sent: Friday, May 25, 2007 10:11 AM
Subject: Re: [RFI] RFI from Astron power supply
> Rod,
>
> I presume that the Astron supply in question is the SS-35 or SS-35M.
Those
> are switching power supplies, but are among the best I have ever seen
> regarding RFI to HF or other radios. I have been using an SS-35M for
more
> than 3 years now and think it is great. Being an EMC engineer, I was
very
> wary of having a switcher in my station (I operate 160m thru 70 cm, so
> that's a lot of spectrum that could get messed up). If the Astron
> switcher is creating RFI, I am guessing that something has gone wrong
with
> the internal circuits and you would probably do best to contact Astron.
>
> Now, if your power supply is one of their very reliable linear series
> (which weigh a proverbial "ton"), then I can just about guarantee that
> something has gone wrong with the internal voltage regulator that drives
> those big pass transistors on the back of the supply. It is not
uncommon
> for linear regulators to "take off" and oscillate, creating sometimes
> extensive RFI. Sometimes the chip itself is bad, and other times the
> problem can happen either because no by-pass cap was used at the input
> side of the regulator or the cap is there but went bad. Again, contact
> Astron.
>
> Either way, I would hope that with only 20 hours of use that the supply
is
> still within the 1 year warranty. If not, you'll still do best (in my
> opinion) to contact Astron and return it. Trouble shooting either power
> supply will involve use of a decent oscilloscope (having at least 50 MHz
> bandwidth) and/or a spectrum analyzer. Either instrument should allow
you
> to find the problem within minutes.
>
> It would be helpful if you were to post which model Astron you have.
>
> 73, Dale
> WA9ENA
>
>
>
> rrath@charter.net
> Sent by: rfi-bounces@contesting.com
> 05/24/2007 11:30 PM
>
> To
> rfi@contesting.com
> cc
>
> Subject
> [RFI] RFI from Astron power supply
>
>
>
>
>
>
> Hello to the list. I have a 35 amp Astron power supply that is giving of
> RFI.
> This p.s. has had less than 20 hrs use. I am charge of the Ham radios
for
> our EOC, where we use this p.s. I just had the local power company RFI
guy
>
> come and we located 9 power poles that are giving off RFI as well as the
> p.s. They will take care of the poles, I need to take care of the p.s.
>
> Any help on what to do to get ride of the RFI from the 35 amp power
> supply?
> The p.s. is giving off about an s-5 to s-7 RFI.
>
> Thank you for any help you can give.
>
> Rod KC7VQR
> W7SCC Trustee
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