You probably came to this web page because you have an Astron supply that has problems. Note that the Astron supplies are advertised with peak duty amperage numbers and in continuous duty can supply only about half of the rated current that is, a twenty amp Astron can in reality supply only about ten amps continuously. Astron marketing gets around that by saying that in normal operation the user listens i. This gives time for the heat sink and pass transistors to cool down.

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You probably came to this web page because you have an Astron supply that has problems. Note that the Astron supplies are advertised with peak duty amperage numbers and in continuous duty can supply only about half of the rated current that is, a twenty amp Astron can in reality supply only about ten amps continuously. Astron marketing gets around that by saying that in normal operation the user listens i.

This gives time for the heat sink and pass transistors to cool down. In other words, the digits in the model number represent the peak intermittent current capacity. In almost all cases you will want to add a fan blowing across the heatsink and a and a second one through the box across the transformer and bridge rectifier is definitely recommended you will need to punch holes and add screening for that - and don't forget to ground the screening.

More notes are below Most of the chip reference sites have the data sheet and applications notes, and the theory and design information you will find there is as true today as it was when the chip was introduced Starting with the design notes is a good idea.

Before you start debugging your Astron, I suggest that you read the first three articles in the "Linear power Supply Design and Theory" section below. The regulator is often placed in under engineered circuits. There are on-chip amplifiers with an incredible amount of gain. Said amps with a lot of open and closed loop gain makes a nice RF sniffer when the designer forgets to properly bypass various sections of the regulator circuit.

Plus there is poor response to high frequency glitches and noise. Proper pre-regulation is another common circuit shortfall. The end result is often seen as erratic operation, false crowbar circuit firing and regulator chip failure. The crowbar circuit itself works well when triggered. Most of the crowbar problems I've seen once past the Astron regulator board were traced to older filter capacitors under relatively heavy loads.

Many Astron power supplies work well for decades, a lot of the problems surface when feeding higher impedance and reactive loads. The load impedance and current demand presented to the supply can be a big factor in its reliability. The regulator chip is an excellent building block, but making one play well with multiple nearby 50kw or higher broadcast transmitters can be a test of ones engineering skills. Fortunately, the data sheet has all the required information.

Much of the mentioned data sheet information is often overlooked. Problems resulting from poor regulation circuit design shortcuts often rear their ugly head at much later dates. One of the overlooked items is the compensation capacitor value - as this web page by Dr. The average Astron has NO compensation cap at all.

The data sheet which you can click on below has a number of sample circuits, and some show no capacitor, some show 15pF, some show pF also spec'd as 1 nF , and the largest is pF 5nF. Do not go any larger than pF. If your supply has a compensation cap you will find it connected from pin 4 to pin 13 on the DIP package, or from pin 9 to pin 2 on the TO-5 round metal can. By the way, the "this country" that Paul refers to on his web page is Australia. That said, if your Astron is going into current limit at random times, this comment from an email sent by Ron Rogers WW8RR is relevant: A VERY common cause of random current limit shutdown in linear Astron supplies is due to the manufacturing process: a bad solder joint on the collector tab of one of the 2N pass transistors.

During manufacture they solder the buss wire from collector to collector. If you take a pair of pliers and grab the buss wire next to the solder joint at each transistor and pull on it, you will most likely find one that will simply pull off.

All it takes is for one of those transistors all wired in parallel to have a bad collector solder joint and all of the source current from the supply tries to flow through the Emitter-Base junction of that one transistor that has the bad solder joint. Immediate current limit mode!! From yet another email to repeater-builder: Another common failure these supplies are full of them is due to the use of TWO diode bridge rectifiers wired in parallel.

You can see this on some of the RS35 supply schematics. They use two 35A bridge diodes that are wired in parallel with three pieces of 10 busbar with no attempt at current equalization. To use a Martha Stewart term, this is A Bad Thing, engineering-wise; at least the designer used current balancing resistors on the pass transistors. Only the positive half of the bridge rectifiers are used; the negative end is left floating. Eventually one diode will short or open, and that often takes the other one along with it.

This causes the supply's primary fuse to blow up. If your supply instantly blows the primary fuse, unsolder the two heavy transformer wires frequently colored yellow from the bridge rectifier terminals and then see if the fuse blows.

If not, check for a shorted main filter capacitor and shorted pass transistors. If all checks out OK, chances are high that one or more diodes have shorted.

They have to be completely unwired to be properly checked. From an email to repeater-builder from an amateur that works in the power supply design field: If you have to replace all of the pass transistors in a supply, and the old ones are 2Ns, 2Ns also known as the ECG do yourself a favor and buy at least 2Ns and preferrably 2Ns instead.

They are drop-in replacement transistors with better performance for a very reasonable price. Why the different original numbers? Astron used different transistors at different times. As the temperature rises, the power disippation goes down.

The internal chip temperature of the transistor is a lot hotter than the case, or the heat sink, especially during long key-down sessions. The characteristic that causes a time lag between internal chip temperature rising and the heat sink temperature rising is called thermal resistance, and the heat sink compound helps to reduce that.

The 2Ns and 2Ns have been found in known-stock Astrons. The 2Ns may have been stock if they were replacements they were very nicely done, and I couldn't tell , the 2Ns and 2Ns were obvious field replacements.

I always check the emitter ballast resistors and I use the 2N exclusively as a replacement as not one supply I have rebuilt with them over 20 has EVER come back to haunt me at least for a pass transistor problem.

What is your time worth? Don't mix the transistor types!!!!!! The emitter ballast resistors do their balancing act only when the transistors are similar. Always replace a dead pass transistor with an identical part number, or if you can't find one, replace all four as a group. And don't go down in ratings - if you find 2Ns do not replace them with 2Ns. If you have to replace the group, and you have 2Ns and don't want to go to 2Ns at least replace them with 2Ns.

Don't forget to use some good beryllium based thermal compound the thick white stuff that is the consistency of axle grease , but don't go overboard - you want just enough to put a thin layer between the transistor and the insulator, and again between the insulator and the heat sink.

Note that beryllium compounds are known to be human carcinogens when inhaled, fortunately the greasy consistency of the heat sink compound prevents any airborne dust, but you still want to keep it off your skin i. See this web page for more details. Yes, it requires a bit of sheet metal work, but it's worth it. If there are two rectifiers in parallel I replace them with one large one. Three 0. Just remember that MOVs do wear out. When the voltage across a MOV reaches the breakover point, the MOV conducts and turns the excess impulse energy into heat.

Problem is, the heat affacts the MOVs internal characteristics - its breakover voltage increases. The next impulse comes along and more of it passes through. If a MOV sees enough action, the equipment protection is compromised to zero and you won't know it this is why the cheap PC "surge protection" power strips are a joke and a delusion - usually all that is inside is one MOV.

Tripp-Lite "Isobars" are much, much, much better. MOVs are cheap, however, and better than no protection at all. If the Astron I'm rebuilding is going to a repeater site I add a voltmeter, an ammeter, and if it's a busy repeater a 24vDC fan or two 12vDC fans in series blowing air across the heat sink Don't forget that the power transformer and rectifier block need additional cooling as well.

It's worth punching a 3 inch or 4 inch diameter hole in the top and bottom, put copper screening over the holes and force some air flow over the the internal components with a second 24v fan All Electronics is a good reputable surplus source for a wide variety of goodies, including voltmeters, ammeters and fans. If you are going to add a fan or two to a repeater site power supply make sure you use a new ball bearing fan - cheap fans use brass or bronze bushings, cheaper fans use plastic bushings, good fans use ball bearings and are worth the extra money - what is a service call to replace a fan going to cost you?

Fans with needle bearings are even better i. From another email to repeater-builder: The stock Astron power transformer has the center-tap grounded, a high current secondary, and a outer AC winding just for the voltage regulator board. The secondary is one winding, with the center section being the heavy high current wire and the two outer sections much thinner wire.

There is no way to fix it short of a new transformer. The inexpensive fix is to abandon the thin-wire section and move the two thin wires to the secondary of an added small separate 24vAC transformer. There is plenty of room inside the cabinet for it. Just remember to print this page and leave a copy inside the case so the next guy will know what the little circuit on the piece of perfboard is for.

The charging circuit is simply a resistor from the battery to the output of the supply this can boil your battery dry! 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.

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. When or if you find the right one then I suggest you print it and stuff a copy inside a plastic page protector, and taped 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 ID's Fortunately everything but the filter caps, transformer, and sheet metal are common Mouser or DigiKey parts.

And I bet you could find the caps if you tried hard enough. Notes: An "RS-" prefix is a standard power supply. I suspect that RS stands for Regulated Supply. An "RM-" prefix instead of "RS-" prefix indicates a rack-mount power supply i.


A look at the Astron RS-35A

This thing is big and heavy. Most ham radio transceivers do not run directly off of mains AC power, but instead operate from about Keeping the power supply in a separate unit from the radio makes the radio lighter and cheaper, and allows the heat from the power supply to stay far away from the radio. It also allows a radio to operate easily off of 12V lead-acid batteries, or automotive electrical systems. I recently purchased the venerable Astron RSA, one of the most popular amateur radio power supplies.


Astron VS-35M Variable DC Power Supply gets an upgraded MOSFET over-voltage circuit

Note: there is an Astron Wireless Technologies company that makes some very nice antennas. It is a totally separate operation with no connections to the Astron Corporation that makes power supplies. 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, and more. The Pyramid Gold Series linear power supplies are very similar in design and capacity to the Astron supplies.

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