Cheap Linear PSU - Will it make the power or not?

[@tomroderick6041]

Good video Jim! I was at the Stone Mountain Hamfest on Saturday for the 50th consecutive time! I bought a similar TrippLite power supply about a decade ago in the bone yard there which I used for my VHF/UHF rigs in the shack for most of that time. It died recently and I have to get it on the bench this winter and see if I can fix it. Thanks for coming to the Hamfest. I have been a Ham since a Novice at 14 and am now 77 years old. Greatest Hobby in the world. Hope to see you again next year there. 73

[@PaulGriffith]

It is common for that type of transistor to use the case as one of the leads, collector. You will have two leads, emitter and base, under it with an insulator between the transistor and the heat sink.

[@FEPLabsRadio]

Right - something I learned since I started tinkering with these things.

[@LeeMcc_KI5YPR]

Traditionally, that insulator was mica. There are some synthetics that can withstand high voltages and heat.

[@KK6USYHamRadioAdventures]

Thanks Jim!

[@t.j.speakman7723]

Thanks Jim.

[@AndyAAzeroAM]

Good Vid Jim. I've bought, recapped and replaced rectifiers on a few of these now. I like how quiet and stable they are.

[@FEPLabsRadio]

Right! - They are great for the money. The power supply is reliable. You get a lot of bang for the buck!

[@WECB640]

I CREATED A MONSTER! You got this Jim. 🙂

[@FEPLabsRadio]

Thanks buddy! I was channeling my inner Hollywood! I got more vids coming up that you will be interested in. It was vintage day at SMHF...

[@ronwolenski-n8wcr]

The reason you didn't get voltage between the chassis ground and the transistor on the back is because the negative terminal isn't tied to the chassis. This is a mod done to stop noise from the A/C ground from getting into the negative lead, that is a mod I did. Also, the big bolt on the bottom is the not a ground point, it is for the transistor . The small screw is for chassis ground.

[@FEPLabsRadio]

Yeah, my mouth got moving faster than my brain on that one.

[@network_king]

I got one just like this, I think got this and another one for like $5-$10 at a garage sale. They knew nothing about them, one the transistor on the back was blown, the other me and a friend troubleshooted and it had a fried regulator IC and that was tripping the crowbar circuit.

[@FEPLabsRadio]

They are legion. I've seen them plenty at hamfests, yard sales, etc. If I can get one cheap (you scored!) repairing them is not usually too complicated.

[@ScottEvans-vk7hse]

The case of the transistor should have voltage, where the bolts secure the transitor are insulated. I have a power supply that I built as a kit and it has 4 pass transistors to give you 20 amps at 50% duty cycle. I don't use that power supply these days, but it would most likely require a re-cap should I ever start using it again...

[@robertmeyer4744]

Nice Power supply ! I have fixed many of them. Mostly Pyramid ones. Astron is higher quality. That one is quite old. They use good caps and still look good. Behind the pass transistor and before the transformer that is a Stud mount SCR . That is not ground on underside . That has a Mica washer under it. Ground is that little screw and connected to ground on power cord. you can test for that . Between the transformer the PC board. Their is a black pot with a wight wheel you can turn. That sets voltage . It is buy the LM723 reg IC. The 2 diodes for that supply are on PCB at end after transformer wires. They PC mount. On the transformer primary their is a RED MOV. That not a cap. It is a surge protector. MOV like GE V150LA20 or something like that. Sometimes V130LA10 or LA20 is used. To read the part number on MOV RED ones. IS V is max voltage. 130/150 volts. AFTER the LA is ebergany level in Jules . 1 to 20 in disk type. They only go bad if hit with a voltage spike. May diss color or test short but remove 1 lead from transformer to test . Them screws on main cap. The biggest one. Sometimes they come loose. just check them. Normally #10-32 fine screw with star washer . That like a 3 AMP SB fuse or so. it is 1/4 in dia glass type bot can use cerminac 3AB type they just 250VAC . Just do not use 32V fuse. 125VAC 3AG type. That metal on transistor 2N3771 is the collector and input voltage to reg. You can put fan on heat sink if using heavy loads . LOL 7A I have the RS 50A and a RS 70M and has BIG heatsinks . I put 120VAC 120MM fans on them. Nice to have to power small stuff. It has current limit. No melting wire . 73

[@FEPLabsRadio]

Hey Robert, yeah after I recorded that, i realized what that was. Mouth was moving faster than the brain.

[@45auto]

Getting zapped is no bueno.

[@lmamakos]

I was curious about the design of this power supply. Poking around on the Internets, I found a schematic of one. It claimed that it had 1N4002 diodes in the full-wave bridge rectifier? How are 1A diodes in a 7A power supply? Maybe the various schematics I found don't actually match what's really in those power supplies?

[@FEPLabsRadio]

I didn't go that deep - if this one had been worked on, it was super clean work. I'd have to go back and check what's in there. I tested on it some more last night, it held right up to 7A, then dropped off the cliff, so whatever is in there is working great.

[@hazer72]

looks like there's still new stock of those at some retailers

[@FEPLabsRadio]

Yes, I didn't know if that model was still in production, but for $40 - a serious bargain for a decent power supply. I did look it up on HRO this morning. Yep, scored a deal.

[@FEPLabsRadio]

According to this guy ^^^^ because he knows secret transistor code, the pass transistor was manufactured in late 1981 - so this thing is older than I thought.

[@TheSmokinApe]

If you call them they can look up the serial number and tell you the date

[@FEPLabsRadio]

Son, I am too lazy to call, however, someone else pointed out the manufacturing date on the pass transistor is 1981.