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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