Failed Motorola 10261 ... transistor?

[eccerr0r]

I was able to find another psu of the same type and used standard JEDEC numbering.

The 10261 is a 2n3055 and the 10262 was a 2n3773 in that photograph, so my hunch was correct that the 2n3055 was not a good sub for the 10262... And clearly the 10262 is NOT PNP!

The 2n3771 is also probably not a good fit due to low Vcemax. Hum.

Now, whether or not to buy (what? buy?) "new" (NOS?) transistors or not.

[eccerr0r]

No. these are very much so alive just like some other real old transistor numbering.

Hmm. looks indeed like some people are still making them, did see some of the TO-3 transistors I have that were marked as "obsolete" on mouser/digikey... and it'll be a cold day in hell that I'll pay $155 for one...

[CapLeaker]

Hmm. looks indeed like some people are still making them, did see some of the TO-3 transistors I have that were marked as "obsolete" on mouser/digikey... and it'll be a cold day in hell that I'll pay $155 for one...

TO3 aka TO204.
I just checked Mouser for 2n3773’s and they had over 300 in stock for CAD$10.80.

[eccerr0r]

Well, I don't have a 2N3773 but have a 2N6057 which I'll happily trade for a few 2N3773's..

[CapLeaker]

Well, I don't have a 2N3773 but have a 2N6057 which I'll happily trade for a few 2N3773's..

Careful here now. The 2n6057 is a Darlington transistor.
I've always got a stock of 2n3772, 3, 3055, MJ15001 and other popular transistors home. I repair a lot of linear PSU's so I need these all the time. I don't stock TO3 aka TO204 Darlingtons. Hardly ever need those.
If I would be closer, I'd just send some down to you,

[eccerr0r]

Yeah, I happened to have a bunch of darlingtons and was tempted to remove the 10261 driver transistor, short B to E, and just use darlingtons directly instead of using the 10262's since it was darlington connected already. But I figure if I could use regular BJTs I wouldn't have to do this mod...

Kind of weird, a lot of linear PSU's I've come across including this one, the pass transistor is indeed darlington connected... just that I've never seen an actual darlington transistor actually used. I've only seen darlingtons used in audio amp finals...

[CapLeaker]

Yeah, I happened to have a bunch of darlingtons and was tempted to remove the 10261 driver transistor, short B to E, and just use darlingtons directly instead of using the 10262's since it was darlington connected already. But I figure if I could use regular BJTs I wouldn't have to do this mod...

Kind of weird, a lot of linear PSU's I've come across including this one, the pass transistor is indeed darlington connected... just that I've never seen an actual darlington transistor actually used. I've only seen darlingtons used in audio amp finals...

Usually linear power supplies go like this: regulator (723) that drives an NPN driver transitor (tip29) and that in turn drives the pass transistors 2n3771, 2 or 3.
In order to use a Darlington pair transistor here, you would have to take the tip29 out and connect the base of the 5067 where the base of the tip29 was. Basically you are skipping the driver stage, because you got an extra transistor built in that gives you the gain in one package.
Not sure why the reasoning, but most normal linear power supplies do not use the Darlington as pass transistors.

[sam_sam_sam]

Usually linear power supplies go like this: regulator (723) that drives an NPN driver transitor (tip29) and that in turn drives the pass transistors 2n3771, 2 or 3.
In order to use a Darlington pair transistor here, you would have to take the tip29 out and connect the base of the 5067 where the base of the tip29 was. Basically you are skipping the driver stage, because you got an extra transistor built in that gives you the gain in one package.
Not sure why the reasoning, but most normal linear power supplies do not use the Darlington as pass transistors.

Come to think of it you are right about 723 regular ic chip some of these circuits used the 2n3055 ( or might have been a different part number I would have to find one of them and look to see for sure which one was used I think I still have a couple of circuit boards that has this setup they were used ) in the Radio Shack 10 amp power supply that use to sell many years ago I have several of them in one of them I removed the circuit board and reconfigure it for a different purpose and application which unfortunately I have not used in many years

The 3 amp version used a different circuit but if I remember correctly it also used a 2n3005 transistor and used a different circuit to achieve the same voltage but just lower current output

Here is a circuit that uses the LM723 and the 2n3055

https://www.eleccircuit.com/variable...3ca31402n3055/

You might be interested these are on sale right now

Marvelous Deal! G25573 - Motorola MJ1000 TO-3 Steel Case 10Amp NPN Darlington

https://theelectronicgoldmine.com/products/g25573

[CapLeaker]

Come to think of it you are right about 723 regular ic chip some of these circuits used the 2n3055 ( or might have been a different part number I would have to find one of them and look to see for sure which one was used I think I still have a couple of circuit boards that has this setup they were used ) in the Radio Shack 10 amp power supply that use to sell many years ago I have several of them in one of them I removed the circuit board and reconfigure it for a different purpose and application which unfortunately I have not used in many years

The 3 amp version used a different circuit but if I remember correctly it also used a 2n3005 transistor and used a different circuit to achieve the same voltage but just lower current output

Here is a circuit that uses the LM723 and the 2n3055

https://www.eleccircuit.com/variable...3ca31402n3055/

You are mostly correct. The 2n3055 were used in cheap, small power supplies something under 5 amps. The 2n3771, 2 or 3 were used on heavier power supplies that had one or more pass transistor depending on amperage.

There are 2 files below. A PDF of an Astron and a pic of a linear PSU using a Darlington as a pass transistor.

[sam_sam_sam]

You are mostly correct. The 2n3055 were used in cheap, small power supplies something under 5 amps. The 2n3771, 2 or 3 were used on heavier power supplies that had one or more pass transistor depending on amperage.

There are 2 files below. A PDF of an Astron and a pic of a linear PSU using a Darlington as a pass transistor.

The one you posted is using a LM741 ic chip not the LM723

[CapLeaker]

The one you posted is using a LM741 ic chip not the LM723

Was just an example circuit I had kicking around on my NAS. There are some around using the LM723 and a darlington transistor too... but I didn't feel like going through all of my PSU schematic collection early in the morning.

[sam_sam_sam]

Was just an example circuit I had kicking around on my NAS. There are some around using the LM723 and a darlington transistor too... but I didn't feel like going through all of my PSU schematic collection early in the morning.

I can not blame you on that one

[eccerr0r]

Exactly as said, seems so many high power (3A+) linear PSUs all use darlington structures but not use actual darlington transistors. Perhaps it's just cost?

Past two linear PSUs I worked on was this power one that had the 10261 predriver drive a few 10262 pass elements, clearly in darlington formation. It uses a LM723 to regulate base current of the predriver. Then there's this other 3A 12V PSU I fixed that used a zener as the reference, but used something like a TIP31 as the predriver and a 2N3771 as the pass element, also in darlington configuration.

I just have no idea where the 2N605x's I have came from...

[CapLeaker]

Exactly as said, seems so many high power (3A+) linear PSUs all use darlington structures but not use actual darlington transistors. Perhaps it's just cost?

Past two linear PSUs I worked on was this power one that had the 10261 predriver drive a few 10262 pass elements, clearly in darlington formation. It uses a LM723 to regulate base current of the predriver. Then there's this other 3A 12V PSU I fixed that used a zener as the reference, but used something like a TIP31 as the predriver and a 2N3771 as the pass element, also in darlington configuration.

I just have no idea where the 2N605x's I have came from...

Yeah, just like that Astron. Here is one of my old threads about an Astron repair. Maybe a good toilet read.
https://www.badcaps.net/forum/troubl...ut-voltage-low

[eccerr0r]

Yeah it appears that the astron actually tried to "increase" the limit by having another winding. Same with this power one though it only does it for the 723.

The odd thing with this psu, I took it apart before powering it on for the first time for some reason. Well, I wanted to clean some of the junk out of it and solder two capacitors that were ripped out of the board (bad sign...) so I had to remove the board...

To remove the board I had to pull the transistors, and why not test them... that's where I found the predriver good and the problematic pass element. One had its B-E junction smashed (it was semi-conductive in both directions), and other had a bit of a leak in it, so really both aren't very good The obviously bad one was replaced.

The funny thing about this PSU is that it uses TO-3 diodes for the main bridge rectifier. And woah that was dangerous, if I swapped the two TO-3s by mistake, boom goes the caps... had to carefully mark them down so I don't mix them up...at least the pass transistors it'd still work, just not at full power.

[CapLeaker]

Yeah it appears that the astron actually tried to "increase" the limit by having another winding. Same with this power one though it only does it for the 723.

The odd thing with this psu, I took it apart before powering it on for the first time for some reason. Well, I wanted to clean some of the junk out of it and solder two capacitors that were ripped out of the board (bad sign...) so I had to remove the board...

To remove the board I had to pull the transistors, and why not test them... that's where I found the predriver good and the problematic pass element. One had its B-E junction smashed (it was semi-conductive in both directions), and other had a bit of a leak in it, so really both aren't very good The obviously bad one was replaced.

The funny thing about this PSU is that it uses TO-3 diodes for the main bridge rectifier. And woah that was dangerous, if I swapped the two TO-3s by mistake, boom goes the caps... had to carefully mark them down so I don't mix them up...at least the pass transistors it'd still work, just not at full power.

Oyyyyy! Made a good story though! My landscape at work is everything from the mid seventies up to modern equipment. The folks that know things about old equipment is getting rarer every year and parts too…

Back to these Darlington TO3 transistors… since you have a bunch of them, I think they came from an audio amp or a large power supply. Anything else doesn't make much sense having a lot of these.