Question about Pyramid 10 AMP 13.8V POWER SUPPLY Car Audio Amplifier

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Pyramid PS-21K Power Supply HELP!

I replaced the four 2N3055's in the back of unit but now instead of 13.8 volts its doing 19-21 volts. What did I do wrong? Something in the wrong Place?

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Check the resistors that bias the transistors, and also any zeners connected to them.

Posted on Jan 02, 2009

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2 Answers

Pyramid power supply model ps-8kx started putting out 20 plus volts and the amps evidently dropped cause it will not power cb now when you key mike and no it's not a dual final radio


Sounds as though the regulator transistor/s have gone bad. Check these parts by taking them out of line(disconnect them from any wiring) and check for shotrs or opens with a transistor checker or VOM.
If I can be of any more help, please email me at wyoed1@aol.com. "Original Radio Man" Ed

Feb 12, 2013 | Radio Communications

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Power supply seems to work fine until it has a load on it. Puts out 13.8 volts, but will only handle about 2 amp load before the overload protection kicks in. My 2 amp load test is an 1157 light bulb and...


Note: I'm answering your post with the assumption that you plan on using this power supply with a computer. If this is not your intention, please disregard my solution attempt.

You likely already know this, but if you are powering a computer you're going to need a power supply with more wattage. I would recommend nothing less than a 350 watt power supply.

Follow this link to calculate how much power you need to run your computer: http://www.extreme.outervision.com/psucalculatorlite.jsp

If you're not ready to give up on your 270 watt power supply, then remove all PCI/PCI-E devices, USB ports, extra fans, non-boot hard drives, extra DVD/CD drives etc. one at a time until the computer powers up. Anything you can do to reduce the load on the power supply will help.

Good luck and thanks for using FixYa.

Mar 08, 2011 | Pyramid PS14KX 270-Watt Power Supply

1 Answer

Ps 52 kx power supply will not hold load


thank you for your help . I have already fixed the power supply I double checked the transisters and found three bad so I replaced all the power transisters and it is fine . thanks again bob

Nov 17, 2008 | Pyramid - PS21KX 20 Amp Power Supply Car...

1 Answer

Pyramid ps-36kx


Generally, the fuse only blows when the rectifiers fail. In other Pyramid supplies, they use a square, 4 terminal bridge rectifier. They probably use the same thing in your supply.

Let me know if you have any other questions.

Nov 15, 2008 | Pyramid - PS21KX 20 Amp Power Supply Car...

2 Answers

Pyramid ps-15kx


Unplug the PS-15KX 120V AC cord !! Then take cover off. DO NOT plug the AC cord in unless you are used to working around a lethal voltage and current !!!!!!!!!!

If you can use a Multimeter, then measure resistance across each pair of the 3 leads of the output transistors. You will probably find fractions of an ohm across a pair of leads. One or both may be shorted. NOTE: Do not ever measure resistance in a powered up circuit, kiss meter bye-bye and maybe burn you too.

By putting more robust transistors in this supply, you may not gain much reliability. The supply is rated at a continuous current draw, which is less than the intermittent current they advertise. Read the spec's of any power supply you get and look for continuous current ability.

There are several better transistors that will substitute for the 2N3055. You will need to look at a transistor substitution book and check specs. The internet is great for this. I used to use all kinds of data books, and still have them! But looking up info on-line is nice. Motorola has some that will fit and have higher current and voltage ratings,

Get someone who is a ham or geek if you aren't sure about sticking your fingers in the power supply.

Be Careful, Work Safe, it is a factor of longer life.

Nov 08, 2008 | Pyramid 10 Amp Power Supply (068888701655)...

1 Answer

Pyramid ps-21k power supply


you need to get the voltage regulator circuit checked in your ps-21k

Jun 13, 2008 | Pyramid 10 AMP 13.8V POWER SUPPLY Car...

1 Answer

PS36K power supply overload problem


Most of Pyramid's supplies are based on the LM723 voltage regulator. The DATASHEET should tell you most of what you'll need to know to repair it. THIS is the schematic diagram.

If the output voltage drives the voltmeter to the end of the scale, it likely has one or more shorted power transistors.

Dec 21, 2007 | Pyramid - PS21KX 20 Amp Power Supply Car...

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