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.

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.

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.

5 years later! Still enjoys it! Thanks

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.

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!

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.

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.

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.

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.

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

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

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.

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.

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.

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.

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

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

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

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

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

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.

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!

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

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.

I love all your information and helpful hints!

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

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.

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.

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...

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.

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

Thanks for making these repair videos. Great Video

Great visual explaining the importance of thermal conduction. Thanks Paul

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

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

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

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

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

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.

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!!

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.

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!

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 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!

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.

Wow! What a great lesson again! Thank you!

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

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

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

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

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.

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!!!

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

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

That Dynaload is a beast!

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.

Learned a bit about a similar Astron power supply. Thanks

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.

Awesome video, I could follow along all the way this time, no homework!

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.

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

Another great job of teaching.

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

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. :)

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

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

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.

" 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.

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

Nice job.Thanks for all the great info.

Mr. Carlson is my Mr. Wizard. Thanks for teaching us.

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 fantastic video Paul. Thanks very much. Jim

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

Thanks for sharing this. I learned a few things.

Excellent, after watching I went back and found the short. Thank you

quality person with some integrity for others people's equipment

The best man within his field on YT 👍🏻

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.

Great channel, Mr Carlson!

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.

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

the world needs more people like you, sir!

Great video! Greetings from Poland :)

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!

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.

Thanks, I watched the entire video and learned a lot!

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

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

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

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

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!

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.

Very well done video and explanation. Thank you