Note: there is an Astron
Wireless Technologies company that manufactures some very nice antennas. It is a totally
separate operation with no connections to the Astron Corporation that makes power supplies.
|The contents of this page, like almost every page here
at www.repeater-builder.com, are totally dependent on donations of information.
If you have a hint or a useful trick please consider writing it up and sending it in.
Please consider sending us a scan if you have an Astron schematic that we don't list below.
If you don't have access to a scanner we can scan a good clean copy.
We have received emailed requests for schematics on the model BB-30M, SS-10 and SS-25 / SS-25M
supplies. Does anyone have one to share?
Astron makes both linear and switching power supplies, and some other products.
You should read this Astron Introductory
Information article before any of the other articles here in the Astron section
It has some very useful information on the Astron linear and switching power supplies, with
background, history, model-specific information, both repair and modification suggestions, photos,
Astron Linear Power Supply Reset Circuits
Astron Linear Power Supply Articles and Modifications
- Float Modification for the RS/RM-35A/S
Schematic of the Astron RS-35A/M with float
modification (the yellow highlighted area)
If you add a toggle switch to the front panel that shorts out the added resistor you can label it
"Float" (when off / open) and "Normal" (when on / shorted).
Make sure you print the mod sheet and tuck it inside the supply for the next guy...
- Adding Anderson PowerPole Connectors to an SS-30
supply By Robert Schulz KC6UDS
This is a very nicely done modification that extends the usability
of the SS-25 or SS-30 supply.
Kyle Yoksh KØKN took Robert's idea and modified
a Daiwa PS-304 power supply in a similar fashion.
- Reducing Inrush (Surge) Current on Astron Power Supplies
by Robert W. Meister WA1MIK
This modification adds a thermistor in series with the transformer, reducing the surge current
and eliminating annoying circuit breaker trips on the larger linear power supplies. This same
mod could be done to other high-power supplies.
- Installing a New Regulator Board in an Old Astron Power
Supply by By Tom Dailey WØEAJ
After the board burned up, Tom bought a new one from Astron. Seems they've made a few changes in
the design since his supply was made. This article describes what he discovered and how to deal
with putting a new board into an old supply.
- An evaluation of a 2009 Astron RS35M supply
by Stu Martin K2QDE (2.5MB PDF)
Stu opened his brand-new supply and took several photos, showing what's been added or changed.
He scanned then redrew and corrected the schematic so it matched the actual unit; this drawing
can be found as a PDF file below.
- Replacing Astron Meter Lamps
by Larry Lockard N7FM (off-site link)
A very well-written article that shows how he replaced the "unreplaceable" internal meter lamps,
which seem to be two 14V bulbs wired in series and powered by the raw unregulated voltage.
- Restoring / Rebuilding an Astron RS35M
by John Keith W5BWC (1.3MB PDF)
While this is listed as a "restoration" it's actually a complete gut job with only the
transformer and chassis remaining. Everything else gets replaced with a completely different
- Repairing Astron 13.8V Linear Supplies
by Robert W. Meister WA1MIK
General linear power supply circuit explanation, followed by the most common problems,
diagnostic techniques, and repairs for these units.
- Annotated RS35M Schematic
by Jim Larsen AL7FS (170kB PDF)
Jim Larsen, AL7FS (the ARRL Alaska Section Manager) took that QST article and the schematic
and produced an annotated schematic that takes advantage of the annotation function of the
PDF file architecture. Use a recent version of the Adobe Acrobat reader and just mouse over
the yellow folder symbols. Worth studying.
Astron Linear Power Supply Battery Back-up Modifications
If you inspect the circuit diagram you will see that the BB option is simple - it consists
of a pair high current diodes wired cathode to cathode, with one anode going to the supply,
and the other to the battery bank, and the cathodes feeding the load. This configuration
allows either the power supply or the battery to feed the load. In the low current supplies
they use half of a bridge rectifier, in the high current supplies they use two separate diodes
in parallel for each current path. The charging circuit is not well designed as it is just a
single resistor from the battery to the output of the supply (look for R103 in the schematic
for the RS-12-BB and RM-35A-BB)... and this overly simple charger circuit can boil your
battery dry! Since this design uses the supply voltage as the charging voltage you must have
the supply voltage set EXACTLY to the voltage that is the sum of the diode voltage drop plus
the battery float voltage... regardless of what the voltage your load wants to see (and the
voltage drop across a diode varies somewhat from low-load to full-load). Overly simple
charging circuits ALWAYS leave lots of room for improvement.
The rule of thumb on maximum charging current for nickel-cadmium or lead-acid batteries
is no more than 1/10 of the amp-hour capacity of the battery. Therefore a 20 amp-hour battery
has a maximum charging current of 2 amps.
There are two major flaws with the Astron charger design:
- First, the charging current is limited only by the voltage difference between the Astron
voltage output and the voltage of the battery limited by a series resistor. That resistor has
a value of 10 ohm 10 watts in the RS-12-BB, 5 ohms 10 watts in the RS-20-BB
or RM35-BB or 1.6 ohm 15 watt resistor in the RM-50-BB (and that resistor is made
from three 5 ohm 10 watt resistors in parallel). Under conditions of a dead battery
the initial charging current can be higher than the battery can take - in the RM-50-BB that 1.6
ohms at 14v delivers between 8 to 9 amps (and that's not documented anywhere). On a RS-12-BB
the max charging current is about 1.4 to 1.5 amps... The three RS-12-BBs I have seen at radio
sites have all been tied to batteries in the range of 7 to 20 amp-hours. Do you see a
potential overcharge problem with the 7 amp-hour battery?
As mentioned above the maximum charging current is less than 1/10 of the amp-hour capacity of
the battery. Therefore a 20 amp-hour battery has a max charging current of 2 amps. The RS-50-BB
charge current into a dead battery is 8 to 9 amps? Oops.
- The second flaw in the Astron design is that the 8 to 9 amps flowing through the charging
current limiting resistor in an RS-50-BB dissipates around 100 watts.... oops, POOF! There goes
the three paralleled 5 watt resistors. Now you have no battery charger and who knows what
was damaged with the excess heat from the fried resistors.
Now in real life, the battery voltage is not going to be zero, so the difference voltage is
not going to be the full Astron output of 14 volts and the charging current is going to be
less than 8 amps, but still... there are better charging circuits out there than a 14 volt
50 amp power supply and a single undersized current limiting resistor. Especially
with the extra requirement that the supply voltage has to be set to the battery plus the series
diode voltage drop (no matter what voltage the load - your repeater system - wants to see).
If you need a battery backup system for your repeater, I would do one of two things:
- First, leave out that charging resistor (R103 or its equivalent in larger supplies) and use
an external multistage charger outside the housing of the Astron. There are good ones out
there, I've had excellent results with a high-end "Battery Tender" made by Deltron
- Second, replace R103 with a multi-stage charger board added inside the Astron cabinet.
I've seen an Astron where the owner mounted a DC toggle switch (I'd use a toggle-type-circuit
breaker) of the appropriate amps rating on the front panel of the supply near the diodes, wired
it in series with the R103 charge current control resistor and labeled it as "Internal
Charger Enable / Disable".
If you are going to "roll your own" high current BB conversion, and you don't mind a
"non-pretty" implementation, then a part of the diode array from a high-current alternator
will work just fine. The normal "12 volt" automotive alternator diode array has six diodes
in it (or sometimes 12 in 6 groups of 2 in parallel or 18 in 6 groups of 3 in parallel),
and the metal plates with the diodes mounted in them are usually tossed in the trash if
one diode is dead. A long time ago I needed to swap out the alternator in my old 1971
Dodge Dart DEA undercover chase car... (that was a FUN car to drive...) I used the
visit to the alternator rebuilder to pay $5 for a three-diode common-cathode array out of
a 120 amp alternator that had one bad diode that was on the end of the plate.
When I got home I mounted the diode plate in a bench vise and used a drill and hacksaw
to remove the bad diode out of the end piece. This gave me two good diodes and enough space
around the diodes to allow drilling a couple of mounting holes. Using that diode plate
mounted on standoff insulators I ended up with the same circuit as the Astron BB option
at a cost of $5 plus the standoffs... and in the proof-of-concept prototype the plate was
held to two pieces of wood by some drywall screws. The final version used polystyrene rod
for the insulators. All of this was done a couple of years before Astron came out with
their BB option. Nowadays it may be easier to just buy the BB version from Astron - but
sometimes it's more fun (and more educational) to roll your own.
- Schematic of the RS-12A-BB Factory
Battery Back-Up Schematic donated by John Lund
- Schematic of the RS-20A-BB Factory
Battery Back-Up Schematic donated by Rick Williams N8EDR
- Schematic of the RM-35A-BB / RM-35M-BB
Factory Battery Back-Up Schematic donated by Larry Horlick VYØHL
Note that the schematic title block says that it is for both the RM-35M-BB (rack mount,
w/meters), and the RM-35A-BB (rack mount w/o meters), but the schematic does not show
any metering components. If you need metering look at the next one and copy that
The metered version of this supply is also known as a Motorola RRDN6933A, which comes
with lighted meters (the first that anyone that I know has seen with that feature).
- Schematic of the RS/RM-50M-BB Factory
Battery Back-Up Schematic donated by Robert Burton KD4YDC
Schematic Diagrams of Astron Linear Power Supplies
Please realize that you will find multiple different schematics listed below for the same
supply as the designs changed over the years due to parts availability, circuit improvements,
etc. For example, the early supplies use discrete stud-mounted diodes instead of half of a
bridge rectifier (switching to a epoxy bridge module, despite the fact that only half is
used, is one of the tricks that the designer at Astron used to lower the parts cost and
manufacturing labor cost). You may have to download more than one schematic to get the one
that matches your supply, and you may not find your schematic at all (as we only have the
ones that were donated to us). If you have one that we don't, please consider sending us a
scan or a Xerox copy.
We have received emailed requests for schematics on the model BB-30M, SS-10 and
SS-25 / SS-25M supplies. Does anyone have one to share?
When (or if) you find the schematic that matches your unit I suggest you print it and stuff
a copy inside a plastic page protector, and tape it to the underside of the lid of the power
supply cabinet! Several folks have mentioned in emails and on mailing lists that you can call
Astron on the phone and you will hear them tell you that they don't have electronic copies of
their drawings and they don't know how to email them. Trust me, the person that answers the
phone will be amazed when you tell them that the drawings from different years for the same
model power supply show some different component ID's and values. Unfortunately this is
important because if one chooses to buy replacement parts (from Astron) they (according to
Astron) need only to supply the model and component IDs... Fortunately everything but the
filter caps, transformer, and sheet metal are common Mouser or DigiKey parts. And I bet you
could find the capacitors if you tried hard enough. Astron has to get them from somebody.
So leave off the prefixes and suffixes and first look for the basic model number as opposed
to the specific model.
- An "RS-" prefix is a standard power supply. I suspect that RS stands for Regulated
- An "RM-" prefix instead of "RS-" prefix indicates a rack-mount power supply (i.e.
packaged to mount in a 19 inch rack). This packaging is only offered on the larger
supplies. If you need to rack mount a smaller one, just use a rack shelf. Usually
there is little (if not zero) electronic difference between the RS- series and the
similar RM- model.
- Change the first letter from R to V and you have one with front panel adjustments
(V=variable). Converting a RS or RM to a VS or VM usually involves adding two
potentiometers to the front panel and making the wiring changes shown in the schematic.
- SS- series are Small Switching power supplies. Their schematics are further down the page.
- SL- series are Small Linear power supplies. Their schematics are further down the page.
These have room for a two-way radio to be mounted inside the cabinet. The SL series suffix
indicates the make/model radio they were made to work with. Check the catalog pages on
Astron's web site for all the details.
- LS- and VLS- series are Linear Special-voltage power supplies, usually 28 volt.
- A trailing "M" indicates front panel Meters. Newer supplies (possibly starting around
2008) have illuminated meters.
- A trailing "L" indicates there's a cigarette Lighter socket on the front.
- A trailing "S" means there's a Speaker inside the case.
- A trailing "BB" indicates the Battery Backup option. See the comments above on the
battery backup feature.
Astron builds supplies for several manufacturers - for example a Kenwood KPS-12 is based
on the Astron RS-12, the Motorola RRDN6933A is an RM-35A-BB and
the Motorola HPN9041 is an RS-20 variant.
Astron also builds custom supplies for Motorola, GE, Icom, E.F. Johnson, Kenwood,
Uniden and Vertex. For example, the Astron SL11RRA is a 13.8V 11AMP unit specifically
designed with a metal sleeve built into the on top of the cabinet. The sleeve is sized so
that a MaxTrac, Radius or GM300 mobile can slide into it
here for a photo).
A conversion list of Motorola to Astron model numbers can be
Donations of additional schematics for the library below are
always welcome !!
Send them to the maintainer listed at the top of this page (you will be credited
unless you tell us to assign it to A. Nony Mous).
See the "Notes" section above for an explanation of the prefix and suffix letters
If you don't find the schematic for your Astron below, then we were not given it. If you find
one somewhere else that we don't have, we'd appreciate a scan.
- RM-60A, RM-60M 42 KB PDF,
dated 08-16-1988 donated by Tom Allinson WB6DGN
- RM-60A, RM-60M 395 KB PDF,
dated 08-16-1988 but dated on the lower left of the schematic 03/20/96 Donated by
Mike Morris WA6ILQ
The RM series has a 60 amp model, the RS series does not. At
the moment this is the only RM-specific model in the library.
- RS-3A and RS-4A 364 KB, dated 12-89
Donated by Oscar Ramsey NV3G
(The draftsman obviously started with the RS-7 schematic...
he forgot to adjust the voltage table... it shows a 7 amp load...)
- RS-7A 70 KB, dated 10-94 Donated
by Mike Morris WA6ILQ
- RS-10A, RS-10S 105 KB, dated 9-81
Donated by Bill Netzlof KL7IGB
- RS-10A, RS-10S 368 KB, dated 9-88
(but rubber stamped Sept 22 2003 on the drawing) Donated by George Franklin
- RS-12A 199 KB, dated
11-83 Donated by Richard Reese WA8DBW
- RS-12A, RS-12M 125 KB,
dated 6-88 A. Nony Mous found this on a Russian web site and forwarded it.
- RS-12A, RS-12M 42 KB PDF,
dated 6-88 Donated by A. Nony Mous
- RS-12A-BB 119 KB, dated
January 2000 donated by John Lund. See the comments above on the battery backup
- RS-12A, RS-12M 1.01 MB,
dated 11-2009 donated by Greg Shaw N4GOS
- RS-20A 71 KB, dated
11-12-1978 Donated by Gary Eldridge KC8UD
- RS-20A, RS-20S 79 KB,
dated 9-23-88 Donated by Kevin Custer W3KKC
- RS-20A, RS-20S 185 KB,
dated 9-24-88 Donated by A. Nony Mous
- RS-20A-BB, RS-20M-BB 330 KB,
dated 01-2000 Donated by Rick Williams N8EDR See the comments above
on the battery backup feature.
- RS-35A 135 KB,
dated 1-11-1978 Donated by Joe McIntyre W4DEX
- RS-35M 46 KB,
dated 4-87 Donated by Kevin Custer W3KKC
- RS-35A, RS-35M 216 KB,
dated 4-87 but different Donated by Mike Morris WA6ILQ
- RS-35M 47 KB, dated 4-87,
again different Donated by Mike Morris WA6ILQ
Thanks to Ed Lambert K1ZOK who pointed out that there was an important error in
this schematic file (the repeater-builder staff edited the image file and
corrected it). There was an extra "line" drawn between the collector of the TIP29
and the base connections of the pass transistors. This, effectively, shorted out the
regulator driver Q2. If you downloaded this schematic in the past you may want
to get a fresh copy and replace your incorrect copy.
- RS-35A, RS-35M 555 KB PDF,
dated 09-88 Donated by Jim Bacher WB8VSU
- RS-35A, RS-35M 900 KB PDF,
dated 5-91 Donated by Mike Morris WA6ILQ
- RS-35A, RS-35M 87 KB PDF,
dated 5-95 Donated by Mike Morris WA6ILQ
- RS-35M 498 KB JPG,
dated Jan-2000 Donated by A. Nony Mous
- RS-35M 75 KB PDF,
dated 10-2009 Redrawn, corrected, and donated by Stu Martin K2QDE
This is probably the newest, most up-to-date schematic available. Includes meter
- RM-35A-BB 76 KB PDF,
dated January 1993 donated by Larry Horlick VYØHL
This is a factory Battery Back-Up supply that is also known as a Motorola RRDN6933A. See
the comments in the battery backup section above concerning this particular supply.
- RS-50M 182 KB, dated
dated Jan-2000 Donated by Kevin Custer W3KKC
- RS-50A, RS-50M, RM-50A, RM-50M
44 KB PDF, dated 03-21-96 donated by Tom Allinson WB6DGN
- RS-50A-BB, RS-50M-BB 127 KB,
dated 7-95 Donated by Robert Burton KD4YDC See the comments above
on the battery backup feature.
- RS-70A, RS-70M 87 KB,
dated 4-87 Donated by Henry Clark KC4KZT
- RS-70A, RS-70M 73 KB,
unreadable date (probably 8-88) Donated by Mike Morris WA6ILQ
- RS-70A, RS-70M 227 KB,
dated 6-97 Donated by Avent Lane
- RS-70A, RS-70M 69 KB PDF,
dated January 2007 donated by Tom Allinson WB6DGN
- VS-20M 1.02 MB, dated
11-12-78 Donated by A. Nony Mous
- VS-20M 100 KB PDF, dated
9-86 Donated by A. Nony Mous
- VS-20M 74 KB PDF dated
January 2000 donated by Larry Horlick VYØHL
This supply is also known as a Motorola RRDN6082A. The Moto invoice says "VS-20ML".
- VS-35M 322 KB, dated
01-87 Donated by Steve Duncan, WA4ITA
- VS-35M 322 KB, dated
01-2000 Donated by Bill Neuman, WB9EFP
- VS-50M 25 KB PDF, dated
8-82 Donated by Bob Shields, KA9TYL
- VS-50M 70 KB PDF, dated
11-95 Donated by Tim Bovard, Senior Technician at Nichols & Simpson, Inc.,
Organbuilders in Little Rock, Arkansas.
- VS-70M 132 KB, dated
6-30-95 Donated by Brian Palmersheim KBØETC
Schematic Diagrams of Astron Switching Power Supplies
- SS-12 switching supply 55 KB, Dated
8-22-1996 Donated by Eric Lemmon WB6FLY
No parts values other than what Eric noted.
- SS-18 switching supply 351 KB,
Dated 11-03-1998 Donated by A. Nony Mous
- SS-30 switching supply 70 KB, Dated
9-25-2000 Donated by Eric Lemmon WB6FLY
There is minimal parts info on the schematic. Further info is available
- SS-30 switching supply 301 KB,
Dated 9-25-2000 Donated by A. Nony Mous
A second copy of the same schematic, but a little more readable.
- A mod for the Astron SS-25 and SS-30 power supplies (and maybe other SS-series) from NU4G:
These two power supplies use a simple normally open "click" thermostat to switch a very noisy
(acoustic noise, not RF noise) fan on and off. The fan noise can be annoying at times, so I've
modified my supplies to make it less so. Open the supply after first disconnecting AC power and
allowing for DC voltage to bleed down. Looking inside you will see two sets of heatsinks near
the rear of the unit. Each heatsink has a thermostat, the left side heatsink has a normally
closed 50 degree C thermostat for the AC input - don't bother it. The right side heatsink has
the fan thermostat mounted to it. The fan thermostat switches DC from the output to power the
fan. If you bridge the thermostat with a two watt resistor of 75 to 100 ohms the fan will be on
continuously, but very slowly. This slow speed is enough to keep the supply cool with very little
noise. Before installing this mod simply running my 756PII on receive was enough to turn on the
fan every 5 minutes or so. With the mod I've only had the fan go to full speed (i.e. the
thermostat closed) while operating RTTY for an extended time on a very warm day.
This mod may or may not apply to other models of Astron switching power supplies.
- 1212-18 Switching Regulated Converter 140 KB,
Donated by Tom Allinson WB6DGN
This unit allows you to use a negative ground +12v device (like a two-way radio) on a -12 volt
battery system (i.e. a 12v positive ground vehicle). The positive side of the input and negative
side of the output is common. Another way of saying it is that this is a ground inverting
- 2412 Switching Regulated Converter 140 KB,
Donated by Ed Lambert K1ZOK
This unit allows you to use a +12v device (like a two-way radio) on a +24 volt battery system
(like in many Kenworth, Peterbilt and other large trucks, for example, fire trucks). The negative
side is common.
Schematic Diagrams of some other popular Astron Linear Power
Back to the top of the page
Back to Home
This page originally created in August 2000 by Kevin Custer W3KKC
Totally rewritten and a number of schematics added on 10-14-2004 by Mike Morris WA6ILQ
Copyright © 2000 and and date of last update by Repeater-Builder.com
The following people contributed information to this web page
(in alphabetical order by last name):
Greg Allison KZ6S (SK),
Tom Allinson WB6DGN,
Jim Bacher WB8VSU,
Don Best N6ALD,
Robert Burton KD4YDC,
Henry Clark KC4KZT,
W.C. Cloninger, Jr. K3OF,
Steve Duncan, WA4ITA,
Rick Eastwood W6RE (ex KB6LJO),
Gary Eldridge KC8UD,
George Franklin WØAV,
George Henry KA3HSW,
Larry Horlick VYØHL,
Jeff Kincaid W6JK,
Ed Lambert K1ZOK,
David Leeper K6DWL,
Eric Lemmon WB6FLY,
Doug Marston WB6JCD,
Skipp May WV6F,
Bob Meister WA1MIK,
David Metz WAØAUQ,
Brian Palmersheim KBØETC,
Mike Perryman K5JMP,
Richard Reese WA8DBW,
Ron Rogers WW8RR,
Robert Schulz KC6UDS,
Bob Shields KA9TYL,
JaMi Smith KK6CU (SK),
Ron Vincent KF4D, and finally
A. Nony Mous and her cohorts.
The Astron logo/image is a registered trademark and is used within this
page with permission from the Astron Corporation.
The schematic images are copyright © Astron Corp. Each one is dated
on the individual drawing. No copyright infringement is intended. If
Astron had the schematic library on their web site we wouldn't need to.
This web page, the hand-coded HTML on it, this web site, the information
presented in and on its pages and in these modifications and conversions
is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC
and multiple originating authors. All Rights Reserved, including that
of paper and web publication elsewhere.