I must apologize. I'm pretty sure I was the one who made these changes 20 years ago. In my defense I was a teenager at the time. We used whatever we had on hand, hence the the series resistors and reused TIP41. I moved the transistor to the other side in an attempt to give it a cooler location. I don't know what we were doing with R4, but I think we wanted something physically larger and higher wattage. It's nice to see a proper repair finally done!

I was the purchasing agent for a fairly large commercial electronics, two-way radio, and towboat marine electronics sales and service company. I bought a ton of Astron power supplies, and they were fairly reliable. I've been retired for fifteen years, so my comment my no longer apply, but, the biggest failure we found was the SCR shorting out as it was not adequate. Our service manager asked me to source a higher value SCR, and the failure rate went way down. I don't remember what I bought at this point in time, but our customers were a lot happier. Thank you for your excellent video.

It's really nice to see that their are techs around that repair things right and do what they can to improve on the design.

Simply want to say, with all sincerity, thank you for the time, care and effort that you put into this and all your videos. You are performing a great service to the art and science.

5 years later! Still enjoys it! Thanks

Enjoyed the video. Finally someone around who can talk tech in plain English and make it understandable. Being in engineering for 40 or so years and retired not many people to talk to these days and who makes it straight forward.

I love that the vacuum tube volt meter has earned a place on the bench, working side by side with all the newer, modern technologies. It just goes to show how well electronic devices and appliances were designed and manufactured back then.

Watching this video takes me back to 1970 and my first real job at Control Data testing linear power supplies. The crowbar circuit was used on the +5v ps which had several 2N3055 pass transistors on large heat sinks. Once an assembly girl got a ceramic electrolytic in backwards and we had a nice bang and shower of debris! I moved on to testing logic cards using a GR logic tester powered by a PDP 8 but that is a story for another day.

I really love your videos. Who would have known that you’d learn something new on a venerable linear power supply? Not only do you fix the problems, you undo other people’s ghetto hacks as well for the longevity of the system! The world truly needs more techs like you!

I wish I found this channel before now. You are an amazing teacher, and your videos are fantastically informative. I’ve got three or four power supplies that I’ve had stuck in a corner needing fixing. With your teaching, watching your videos a few times, I now know what to like for, and how to test it.

Ah ! The old faithful LM723 - I worked on PSs way back in the early 80's with this IC... always a favorite. A pretty straighforward repair video. Well done.

My dad had the same one, or one very similar. It gave many years of faithful service running his ham radio at home; it was on 24/7. He gave it to me a few years ago, and although I don't regularly use it, it still works when I do. Thanks for doing a video about it.

Mr. Carlson, your attention to detail is impressive, as always.

you have some gorgeous equipment in your workshop, & your attention to detail is something I admire. I'm really pleased I discovered your channel.

For late comers, the Astron supplies are pretty much the same as far as the regulator board is concerned. The larger linear supplies have bigger transformers and filter caps. There are sometimes some additional resistors added at the factory. These are shown as "Rx" on the schematic. Also, the transistor Paul replaced is typically a TIP29A. Have learnt all this from Paul's video and documentation and fine articles on The Repester Builder's web site in the process of reviving an RS-20A I scorched. Paul did not make the mistake I did. He went straight to the pass transistors and checked them out. I got fooled and screwed around with the regulator board. (Oh well, at least I know how it works now and am certain that the new parts I replaced are good.) But, if you still cannot find any problems, pop in a new LM723 chip (they're socketed) and that might solve the problem.

We had a lot of Astron power supplies just like that one. If the ac power failed, the power supply would stay off when the ac was restored, until you cycled the on/off switch. As usual, your attention to detail is superb.

I have a Pyramid supply in a box in my basement that I worked on about 20 years ago. At the time someone told me they thought its problem was the transformer as Pyramid had a reputation for developing internal shorts in the windings. You have inspired me to pull it out and take another stab at it this winter.

Mr Carlson's Lab Thank you for explaining how things work and teaching. I learned how power suplys worked with this.

This is great. I love these linears, they are one of the most popular bits of kit around here for all the amateur radio types.

This is a very good illustration of the effectiveness of thermal paste and how important it is to use it. Those transistors were living on borrowed time.

I am a big fan of your no nonsense skill in logical repairs,best regards Colin.

The Astron power supply is done and the owner is happy and Paul is happy, but we are sad, because it's over. Thankfully I still have a back log of awesome video's to watch. So really I'm still happy. :)

So, its under thermal throttle. Most power supplies repair starts with checking capacitor, transistors and diodes. These seems to be the weakest members in the link. I think I am correct. Your videos are excellent and you never seems to miss even minor subtle things. I wish all teachers are like you. I hope I will become a patron and be your student in future. Thank you.

Excellent video! I love your clear explanations and attention to detail. I have owned a few Astron power supplies. One was the 30 amp version of this exact PS. Very interesting to see inside of one and it's layout explained. Your videos are awesome. Thanks!

Wow, a 30 minute lesson that I'll always remember. I'm not an electronics tech. Just a ham operator looking for information about the Astron power supply. Fascinating lesson; thanx!

Yes I did enjoy your very detailed description of the Astron power supply, I have one myself so I really appreciate your description of the power supply circuit and all the comments about properly servicing it. Thank you.

This was a great post. I own the very same Astron power supply. It’s working fine at this point but it’s 18 years old and I’m sure the thermal transfer grease has to be dry. As a precaution, I’m going to remove the transistor’s and apply new grease. I truly appreciate the safety tips regarding the capacitor and the tip about keeping a ground jumper applied during service. Thanks and continue the good work!!!

This has inspired me to drag out an old Astron RS-35A that's been sitting defunct in the closet for nearly a decade. A well done course on the inner-workings of a timeless classic. Thanks!

It's always nice to watch a professional at work. Great videos

Hello there Paul once again. I enjoyed watching you going through this video of the power supply repair and restoration. It 's a long while since I did a complete rebuild on a heavy duty "Lab Gear" power supply that I had purchased from a supplier in Leeds. I knew the psu was faulty when I got it, so had that in mind has to be a repair project. On my first inspection I knew that I was going to be doing a complete re-build. All of the components were like out of the ark. So a shopping list was made up and the new gear purchased. Lord knows what the transformer specs where but the size of it reminded me of a ark welder unit. Plus the gauge of the secondary wires to boot. The original stud diodes where 40 Amp devises. 1 was blown. OC. I asked at the place where I had got the PSU from for as near as poss replacement for it. He had a set of 50 Amp studs that were the same size, so I said I would take those to keep a matched set. I got them for free. I got a identical heat sink to mount 4 extra TO3 power transistors on making a total of 8. By the time I was finished working on it it had Variable voltage control, auto heat sensing for fan cooling and metering for current and voltage. It was something that I enjoyed doing and was proud of my work. By the way the transistors and the stud diodes got plenty of thermal paste Hi Hi. See you later and carry on the good work. 73 de John - G0WXU.

Thank You For These videos, I really appreciate them as they help me to remember how to investigate & repair. After 35 years in the Air Force crewing jets, my electronics skills have some what disappeared in my mind. Thx Again.

This is a phenomenal Channel. Your integrity and attention to detail is second to none. Your ability to articulate knowledge and move logically through a repair is resulting in some very low impedance learning. Thank you.

Another great video Mr Carlson. Your thoroughness, knowledge, and communications skills make you a natural instructor. Looking forward to the nest video.

Nice video Mr Carlson , thanks for making it Power Supplies are a passion for me

Great explanation of how a linear power supply operates, and how correct repair makes a difference vs. a jury-rig repair. Thanks for putting this video together.

oh, Mr. Carlson. I got an astron 20amp that's not working. Now I have an HF rig without a built in power supply, I searched "Astron power supply repair" and sure enough here you are! :) Thank you.

" Your how to " video's " AT Your Own Risk " of course are fantastic. Just wish that you showed more of the back side or inside of the PS , where the transistors plugged in by the heat sink. Great video's keep it going.

I just purchased that power supply new - I want to modify the heat sink to your specs and "improve" on the original design. I think now my supply will last a lifetime because I know how to fix it from the transistors to the sensor - great job fun to watch video

Watching this second time because the repair was that good! If everyone worked like this, there would be a lot less vintage electronics in the landfill...

Incredibly good video, methodically going through all the steps to permanently fix the supply and keep it running, and lots of helpful electrical tips for working on high-current applications (never knew the trick about keeping a short wire across a high-capacity cap while working on the rest of the circuit). Loving your content, keep 'em coming!

Great visual explaining the importance of thermal conduction. Thanks Paul

Thanks you sir for the video. KZfaq is full of people making videos of things they have knowledge about. You are an expert and I appreciate your sharing your skills.

Neat to see some familiar equipment on your bench. I worked for Transistor Devices, Inc. after they moved from Cedar Knolls, NJ to Hackettstown, NJ. I never worked in the Dynaload department but I used a bunch of different models over the three years I worked there to test other power supply equipment.

Great video as usual sir. Thank You. I had an RS-50M years ago. When almost new i actually saw a line of smoke come out of it. I cannot remember details but, after seeing your video, remember the lack of proper heat sink compound on the either side mounted pass transistors. And i also had regulator board issues as this one and i noticed some significant poor factory soldering. After cleaning all that up, i tinned the filter cap board traces and added star washers. Those filter cap screws were really loose i remember. Keep in mind i bought this thing new! After all that i ran it for many years on WSJT at close to 200 watts and had other gear hooked to it with no issues.

There's a right way to repair electronics, then there's kludges. Thankfully, you know how to repair them right. Thanks for the vid, great job.

I love that the vacuum tube volt meter has earned a place on the bench, working side by side with all these newer, modern technologies. It just goes to show how well electronic devices and appliances were designed and manufactured back then!!

Very nice detailed description of the workings of this ham power supply Paul! Also, very good down to earth troubleshooting and repair. Another excellent video. Love it. Tom

That Dynaload is a beast!

Very nice explanation of the power supply and the replacement of the thermoisolating stuff in order to cool down the temperature to the output transistor. Also the variable loads applied before and after the measurements . Thank you very much for your excellent demonstration. A.ballestri.suisse Switzerland

Thank you for this video! I have this same power supply and as old as it is, I'm going to order some Dow Corning 340 thermal compound, a few new TO-3 mica insulators and clean and re-grease the transistors just like you did. I'll just consider it preventative maintenance. Thanks again! BTW: I'm old enough to remember Allied Radio and Knight Kits: that's a blast from the past!

Thanks for this video. I am a pipe organ builder and use this power supply in all the organs. These supplies are very reliable and when they do fail it is usually what you found on this one.

I've had an Astron RS-20A running since 1992! I'm really enjoying your videos! :)

Hey, I have one of those. Many years ago we had a local department store that was going out of busness and had a big sale and every thing was going, even the shelving. When I got there most all was gone however i found a car stereo desplay that already had all of the radios and speakers removed. I looked inside and found this large power supply. I asked the clerk what he would sell this desplay for. He looked at me like I had two heads and then said 15$. At the time I was into CB raido and knew that it would be great to power a moble radio and what ever "accessaries" I wanted to run. I got the thing home and took it apart and found the Astron RS-35A. I have used it for many years with no issues.

This is another great video mr Paul. Lot of things and trick I've got. Thanks 👍👍

Another very good video, one thing that was not discussed was the merit of not dropping too much voltage across the pass transistors. Many people feel inclined to put bigger smoothing capacitors in powersupplies like this, as long as the troughs of the ripple are higher than the dropout voltage of the regulator the capacitor is big enough. Bigger capacitors reduce the conduction angle of the rectifiers and stress the transformer more causing more temperature rise, the pass transistors and heatsink will also get hotter. Once again a very good video with good advice!

Mr Carlson, you have too much gear on that bench. Oh, I mean you need a bigger bench. Seeing people take pride in their work never gets old. Worth every cent. I'm guessing you get a fair bit of repair the repair going on.

You're talking about output transistors and mica insulators. A friend of mine used to be the sound engineer at a local disco ( way back when) He needed four really big power amps to drive the whole sound system. Two of the amps kept failing. These amps were supposed to be top of the line, thousands of $'s. come to find out, the output transistors were supposed to have mica insulators on them with thermo grease on them too. The designers removed the need for the mica wafers and just had the grease. The grease didn't quite keep everything insulated so the transistors shorted and failed. The friend finally replaced them with Crown amps that worked flawlessly.

It is always a pleasure to see your videos. You are so thorough and comprehensive. Thank you cope to show us!

Really enjoyed this one. Thank you for a well done video. Please keep doing more power supplies. I have as special interest in them.

I have an RS12 that I run my security cameras on. It's been running 24/7 for the past 12 years with no problems. I also have an RS20 I keep on my workbench. Both have been 100% reliable. I think they're great.

Another great video. Just wish Mr. Carlson had more videos. Find his videos to be the best on youtube for really teaching the repair concepts in depth. Thanks a million. Kevin

Thank you Mr. Carlson. Very good explanations about this power supply. Very good video too!

Mr. Carlson; First visit, first video...compliments on unscripted, well spoken voiceover...informative, including background and safety info. Well equipped bench, and it looks like you know what to do with all that equipment! 25A through those pass transistor sockets on the Astron is a bit much for me...I realize it would make them a lot harder to check/replace, but I'd be tempted to solder Base and Emitter leads, so socket connections couldn't fail again...RELIABILITY is key...as is use of heat sink compound! '73 KA1RPB

Thank you Mr. Carlson! I have one of these power supplies and the cover is still on. The circuit looks similar to the one described in the 1988 ARRL handbook. Similar specs with crowbar protection. If the time ever comes for service this will be great reference.

Another awesome video Paul! Great explanation. Looking forward to you next !

Good info here. I have a VS-50M that has run basically non-stop since 1985. Next time I clean the interior of it I will check the sockets and put on some new thermal compound. Thanks for your time and effort producing your videos. 73, WG2E.

Got to love repairs that don’t require any parts just some clean up and thermal compound.

I love all your information and helpful hints!

I've got a supply like this. I've "ruined" the antique value by putting some Radio Shack meters in there with modified numbers on the current meter. I've used a voltage meter for both. I also drilled two holes in each meter and installed two white leds. Looks nice. This is the perfect supply for any 100 watt 12 volt radio! 20 amps "continuous" I would like another video describing the ic circuits more, especially why they use a 5 volt circuit for sensing over- voltage and how the error amplifier works. Great video! Thanks!

This guy is a geek man's man! Dude you are awesome! Thank you for posting these videos and educating us. You are an asset to humanity. Cheers! Tony

Thanks for making these repair videos. Great Video

your videos are so detailed and it's easy for noobs like me to understand very clearly

man, I love your precise fixes! simply doing it as it should

Great instructional video. Great repair! Thanks for posting this! I look forward to more of your work. BTW, I have the Astron RS-35M...great supply. Again, thanks...stay safe!

i have the variable version of the supply the VS-35m. The tweaky part of these supplies is the current limiting circuit. They don't just use the voltage across a ballast resistor to drive the lm723 current limit, they pick off a voltage upstream using that 300 ohm resistor which is a Vbe and a diode drop upstream which vary in value with the loading. Then they divide that down using resistors which that 300 ohm is part of. They also hand pick parallel resistors called Rx at time of manufacture for each unit depending on how it measures. The VS-35m is even worse in how it does this using a pot to inject voltage into that divider. A very touchy circuit. Nice job on the rebuild, I do wish you had exercised the current limiting to see if it performed as you thought it should.

quality person with some integrity for others people's equipment

The best video Channel on KZfaq. *****

You do such nice work. You make repairs a bit like art. Why just replace a transistor when you can find a beautiful new heat sink that fits like glove on to the old board. Beautiful job and great explanation.

Wow! What a great lesson again! Thank you!

love your video's...trying to catch up on all of them...Thanks for being on KZfaq...

Excellent video Mr. Carlson using those God given senses of touch are nice to have.

Learned a bit about a similar Astron power supply. Thanks

Enjoyed the video. Over the years, I have had several of these Astron power supplies. They do a good job. They seem to be somewhat sensitive to RF getting in and blowing out the 723. A little RF bypassing will take care of this in most cases. 73

Hello, Mr Carlson, Thank you very much for the reply. I have checked the transistor and it is ok but haven't had time to do more testing now. I am so busy I am meeting myself coming and going. I will let you know what I find when I find it Lol. Have a great day. Thanks, again. Arnold.

Great video as always, nice to see someone who cares enough to do things correctly!

Good repair job on the power supply and a good thing it incorporates a crowbar circuit for protection of devices. You reminded me on checking my 60 amp TrippLite power supply, Thanks.

Hi Mr Carson, I finally got some time to check out the Tatung power supply. found the problem, it was a 5000 uf 100 v capacitor. All is well now. Thanks,Arnold.

You are a great teacher and a genius. Thanks from Boston! 73 KC1ANR

Well, I thought i was good with repair, But you show how to go the extra mile to make sure a PS repair will last at least as long as the caps or the weakest link. you are making me improve my amateur skills , also love the weller soldering gun re wire. Duh Ive always hated the way the switch worked and never thought to re wire it- no brainer , just do it and you get the best tools in the world that work for you.

Just amazing videos. I am in awe of what you do.

I just found this video and it is very interesting. I have 2 Astron RS-20A supplies. One has been running almost continuously since 1988. The other is about 8 years old. The old one has run flawlessly, the newer one has had an intermittent since almost day one. However, it does not go out often enough to motivate me to really dig into it. If I turn it on and it supplies voltage it is fine until turned off. But if it is going to act up it will have zero volts on turn on until I flip it on and off and it behaves. One of these days it will annoy me enough to see what is going on. Thanks for this video!

Another great job of teaching.

Nicely done (of course!), thanks as always for sharing!

I 've been following many of your video,s and they are all well done. You obviously are an engineer or a very good technician. Building circuits for correcting problems impress me a lot. 73 de VE2WNF

I love your videos. I found them be accident and I'm glad I did. I like your attention to detail and your willingness to do things right. Are you an electronic engineer? I'm am an electronics hobbyist and your explanations are very instructional. Keep up the great work..

Another great job, Paul! Keep up the good work. Jim

Thanks for sharing this. I learned a few things.

Nice job.Thanks for all the great info.

This came just at the right time, my RS-35M is down and now I know what to look for. I already ordered new transistors to replace the Chinese junk that someone installed before I bought it and the voltage regulator chip that was replaced by one I can’t find online. I just wish I could find the correct schematic for mine, Astron only has the one prior to my design and the one after… Thanks for the great explanation of the power path and what to look for. 73 WP4TGK

Great video. Got a couple of Astrons here to repair myself.