On Nov 4, 11:00 am, "Jimmie D" wrote:
"Stefan Wolfe" wrote in message

...







"Steve" wrote in message
oups.com...
I pulled an old Astron power supply out of mothballs today. It's a
13.8 volt / 20 amp supply (the RS-20A). I find that there's a
noticeable hum when I plug it in, and I also notice that a small
output voltage of one volt or so is measureable on it even when it's
turned off and unplugged.

What should this tell me about the condition of this supply? As it is
I'm nervous about using it.

This is an old linear supply (I have one too). It could be that due to
years of non-use, the electrolyte in the big filter cap dried out. The 120
cycle hum could be the current through the transformer being overloaded by
foils that are shorted in the cap. In any case, you said 'mothballs' so it
probably wasn't used for a long time so it might be a good idea to replace
the filter cap. Buy one of similar C and V rating online or maybe you can
even find something similar at radio shack.

He doesnt say if its the power supply humming(normal) or if eqipment
connected to it is humming.

Sorry but I cant see Steve, he must have gotten on my kill file some how.

Jimmie- Hide quoted text -

- Show quoted text -

The power supply itself is humming. It's humming fairly loudly, louder
than my other Astron supply. Still, I'm less worried about that than
by the lingering voltage after shut down. I know the Astron's tend to
make a bit of noise.

Steve

On Sat, 03 Nov 2007 17:52:26 -0700, Steve wrote:
I pulled an old Astron power supply out of mothballs today. It's a
13.8 volt / 20 amp supply (the RS-20A). I find that there's a
noticeable hum when I plug it in, and I also notice that a small
output voltage of one volt or so is measureable on it even when it's
turned off and unplugged.

Yet another well thought out topic selected for posting in the *Antenna*
newsgroup.

But, then, what else is to be expected:
Message-ID: . com

On Nov 4, 12:21 pm, Spam Trap wrote:
On Sat, 03 Nov 2007 17:52:26 -0700, Steve wrote:
I pulled an old Astron power supply out of mothballs today. It's a
13.8 volt / 20 amp supply (the RS-20A). I find that there's a
noticeable hum when I plug it in, and I also notice that a small
output voltage of one volt or so is measureable on it even when it's
turned off and unplugged.

Yet another well thought out topic selected for posting in the *Antenna*
newsgroup.

But, then, what else is to be expected:
Message-ID: . com

It received some thoughtful, helpful replies. So yes, I'd say it was
very well thought out and wisely selected for posting here.

On Nov 3, 4:52 pm, Steve wrote:
I pulled an old Astron power supply out of mothballs today. It's a
13.8 volt / 20 amp supply (the RS-20A). I find that there's a
noticeable hum when I plug it in, and I also notice that a small
output voltage of one volt or so is measureable on it even when it's
turned off and unplugged.

What should this tell me about the condition of this supply? As it is
I'm nervous about using it.

Thanks,

Steve

Steve,
Most power supplies with big transformers can hum. I had an Astron
RS-20A for years, and it always hummed. If the humming is really loud
then something may be wrong.

I'm assuming that when the supply is powered up, it is putting out
close to 13.5 to 13.8v. You may want to measure the supply ripple to
see if it is abnormal.

Regarding the voltage present at the output:
Did you check for the same behavior on your other supply?
You didn't say how long after you shut the supply off that you
measured the 1 volt at the output terminals. It is most likely the
huge capacitor has not had time to discharge. A bleeder resistor
accross the capacitor would probably shorten the discharge time. The
way to check is to open the supply, power it up for a minute, then
power it off. Monitor the voltage accross the capacitor. Discharge the
capacitor through a resistor (around 200 to 500 ohms) for several
minutes, then disconnect the resistor, and see if the voltage floats
back up. Some voltage on the capacitor would not be abnormal.
If the power supply operates normally when powered up and the ac
ripple voltage is low, then a bleeder resistor across the cap would
solve your problem.
Gary

"Steve" wrote in message
ups.com...
On Nov 4, 11:00 am, "Jimmie D" wrote:
"Stefan Wolfe" wrote in message

...







"Steve" wrote in message
oups.com...
I pulled an old Astron power supply out of mothballs today. It's a
13.8 volt / 20 amp supply (the RS-20A). I find that there's a
noticeable hum when I plug it in, and I also notice that a small
output voltage of one volt or so is measureable on it even when it's
turned off and unplugged.

What should this tell me about the condition of this supply? As it is
I'm nervous about using it.

This is an old linear supply (I have one too). It could be that due to
years of non-use, the electrolyte in the big filter cap dried out. The
120
cycle hum could be the current through the transformer being overloaded
by
foils that are shorted in the cap. In any case, you said 'mothballs' so
it
probably wasn't used for a long time so it might be a good idea to
replace
the filter cap. Buy one of similar C and V rating online or maybe you
can
even find something similar at radio shack.

He doesnt say if its the power supply humming(normal) or if eqipment
connected to it is humming.

Sorry but I cant see Steve, he must have gotten on my kill file some how.

Jimmie- Hide quoted text -

- Show quoted text -

The power supply itself is humming. It's humming fairly loudly, louder
than my other Astron supply. Still, I'm less worried about that than
by the lingering voltage after shut down. I know the Astron's tend to
make a bit of noise.

Steve
It's more than likely the transformer. Try pushing down or twisting the
transformer. Bolts might be loose, or too tight. You could also try
mounting it with rubber washers; if you do that, you might have to add a
ground lead. The reason the voltage hangs in there is that it has a bigger
cap than your other supply.

Tam/WB2TT

Spam Trap wrote:
Yet another well thought out topic selected for posting in the *Antenna*
newsgroup.

Just follow the thread of logic - The power supply
converts AC to DC. The transmitter converts DC to
RF which is routed to the antenna. :-)
--
73, Cecil http://www.w5dxp.com

The output voltage drops slowly when the unit is switched off. In
fact, I compared the voltage drop on the RS-20A to the voltage drop on
an RS-12A that I currently have in use. The voltage drop on the RS-20A
is much slower than on the RS-12A, and when the voltage has dropped
down to around 4 or 5 volts then it really slows to a snail's pace.
==========
Steve , The above indicates that the electrolytic cap or caps seem to be
OK. That the output voltage on the RS-12A declines faster is that its
electrolytic cap(s) highly likely have a lower capacity value and hence
store less charge.

I do have a RS-50A (not in use) capable of delivering 13.8 V-50 Amperes
, although the terminal connectors look like only good to pass up to 20
Amperes.
There was a sticker showing input voltage 220 V but when removing it,it
shows 115 V The primary winding of the transformer must be
two times 115V. The unit works but hums heavily (the transformer sits
close to the metal enclosure).
I fear that the USA made unit is actually designed for the US power
frequency being 60 Hz ,whereas here in Europe we have 50 Hz.
For large transformers it can be unacceptable to run a unit designed for
60 Hz ,on 50Hz.
When time permits I'll have a closer look.
I would like to sell it in the USA where I shall be shortly for 2 months
,but the unit's weight is prohibitive, (19 kg or 42 lbs) to bring it as
air luggage .


Frank GM0CSZ / KN6WH

Steve wrote:
On Nov 4, 11:00 am, "Jimmie D" wrote:
"Stefan Wolfe" wrote in message

...







"Steve" wrote in message
oups.com...
I pulled an old Astron power supply out of mothballs today. It's a
13.8 volt / 20 amp supply (the RS-20A). I find that there's a
noticeable hum when I plug it in, and I also notice that a small
output voltage of one volt or so is measureable on it even when it's
turned off and unplugged.




Check the bleeder resistor, It sounds like it may be open.


Jimmie

What should this tell me about the condition of this supply? As it is
I'm nervous about using it.

This is an old linear supply (I have one too). It could be that due to
years of non-use, the electrolyte in the big filter cap dried out. The 120
cycle hum could be the current through the transformer being overloaded by
foils that are shorted in the cap. In any case, you said 'mothballs' so it
probably wasn't used for a long time so it might be a good idea to replace
the filter cap. Buy one of similar C and V rating online or maybe you can
even find something similar at radio shack.

He doesnt say if its the power supply humming(normal) or if eqipment
connected to it is humming.

Sorry but I cant see Steve, he must have gotten on my kill file some how.

Jimmie- Hide quoted text -

- Show quoted text -

The power supply itself is humming. It's humming fairly loudly, louder
than my other Astron supply. Still, I'm less worried about that than
by the lingering voltage after shut down. I know the Astron's tend to
make a bit of noise.

Steve

Ralph Mowery wrote:

Cecil Moore wrote:

Dave wrote:
what does the voltage read when it is turned on? an rs-20a is probably
not so old that caps would go bad, and the low voltage left over when
you
turn it off probably means the caps are holding a charge.

Or if anything is externally connected to the power
supply, the left over low voltage can be coming from
that connected device. I have my RS-20 connected to
a deep discharge marine battery. If I forget to
disconnect the battery from the power supply when
I power down the supply, the meter on the supply
displays the battery voltage. I'm told that can
damage the regulator within the supply but that
has never happened to me.
--
73, Cecil http://www.w5dxp.com

I have not done the modification to one, but here is a modification for
the
floating batteries.

http://www.repeater-builder.com/astr...rsbattmod.html

http://www.repeater-builder.com/astr...n-rsbatmod.jpg

There is much info on the Astrom supplies he

http://www.repeater-builder.com/astr...ron-index.html


Thanks Ralph - very interesting reading. My mid 80s vintage RS20A seems to
be falling out of regulation under the ~15A load of my HF xcvr during xmit.
Fortunately for me, I homebrewed a PS from an article titled "An RF-Proof
30-Amp Supply" (ARRL Handbook, 1988-89) that works much better. The output
doesn't start to fall off until the load approaches 27A (using 4 x 2N3771s).
With the exception of the outer cabinet itself, it's entirely homebrew...
fabricated the chassis, made my own photo-etched PCB, and rewound a 750VA
transformer.
73,
Bryan WA7PRC