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Anyone know about linear power supplies, single transistor.

24.20.105.115
Posted on April 12, 2023 at 19:46:29
Coner
Audiophile

Posts: 3703
Location: S.W. Washington state, USA
Joined: November 17, 2001
 Have a 12VDC (13.8) @ 6A for powering CB's, etc. Very bare bones, no circuit board. Anyway, it shows 17V no load, which is too high. Uses one TO-3 as regulator, and wondered if the small resistor on it effects the output voltage. Or what else could be wrong? No schematic found as yet. It's a GSC 6R

 

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RE: Anyone know about linear power supplies, single transistor., posted on April 12, 2023 at 19:58:32
Davey
 There's some other components in there me thinks. A resistor (or two) and probably a zener diode to provide the voltage reference.

17 volts with no load is not indicative of a problem. It's a very basic power supply and needs a load on the circuit to start regulating.

Dave.

 

RE: Anyone know about linear power supplies, single transistor., posted on April 12, 2023 at 21:10:44
Coner
Audiophile

Posts: 3703
Location: S.W. Washington state, USA
Joined: November 17, 2001
 Yes, a tiny diode from rect. bridge to reg. pin, and a 220 1/2w resistor from same pin to reg. case. Nothing looks discolored, etc. Okay, will try a load in the morn. Thx much!

 

RE: Anyone know about linear power supplies, single transistor., posted on April 14, 2023 at 09:11:40
gusser
Audiophile

Posts: 3649
Location: So. California
Joined: September 6, 2006
 Sounds to me like the TO3 pass transistor has a collector to emitter short, this sending the unregulated voltage out directly. 17 volts is about right for the unregulated voltage.

There may be other circuit damage as well so all transistors and diodes should be checked.

 

RE: Anyone know about linear power supplies, single transistor., posted on April 14, 2023 at 09:15:34
gusser
Audiophile

Posts: 3649
Location: So. California
Joined: September 6, 2006
 Linear regulators typically do not require a minimum load. Some switch mode power supplies do.

 

RE: Anyone know about linear power supplies, single transistor., posted on April 14, 2023 at 10:02:03
Davey
 Yeah, I'm aware, but I've seen cases where residual and a high-impedance voltmeter can confuse the issue.
In this instance, I don't think we could say for sure until the PS is measured with a load.

Dave.

 

RE: Anyone know about linear power supplies, single transistor., posted on April 15, 2023 at 08:31:37
Palustris
Audiophile

Posts: 2408
Location: Cape Cod
Joined: September 12, 2008
 Instead of trying to resurrect an unknown device, it seems more practical to simply remove the existing circuitry and build a new unit. The LM350K is a T03 device and the circuit is as simple as can be: two resistors and a Zener diode. Just follow the application notes on the datasheet.

 

Save the transformer, posted on April 15, 2023 at 09:20:24
jedrider
Audiophile

Posts: 15167
Location: No. California
Joined: December 26, 2003
 Buy a regulator board from eBay.

Must be a bulky transformer, too, but you can power multiple regulators from one transformer.

 

RE: Save the transformer, posted on April 15, 2023 at 17:00:32
sony6060
Audiophile

Posts: 1465
Location: USA
Joined: August 8, 2014
 Toss the power supply and buy an Astron.

 

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