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Reviews For: MFJ-4125

Category: Power Supplies

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Review Summary For : MFJ-4125
Reviews: 75MSRP: 100.
Description:
MFJ-4125 13.8 volts 25 amp switching power supply
Product is in production
More Info: http://www.mfjenterprises.com/products.php?prodid=MFJ-4125
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
15754.2
K8DXX Rating: 2023-01-01
Cool Little Supply Time Owned: more than 12 months.
UPDATE January 1, 2023
Well, got the replacement for my 20 year old MFJ 4125. Like other reviewers comment, the new one has more fan noise. Right now, it is sitting on a table powering my IC 7300 with the receiver turned up moderately (no antenna). The RX noise is slightly louder than the power supply. In the future, I might locate the ACPS below the table. Still, not a show stopper for a low priced unit that lasted almost 20 years.

UPDATE - December 22, 2022
Well, geez... don't know what to say. Took this supply out of its travel case and the green pilot light came on and then died. Tried it again... same thing. Tried it a 3rd time and the pilot light stayed on for 30 seconds. Just as I was ready to plug it into my new Xiegu G90 and ZZZZZZZZZZZZZZZZZ and then smoke! Heaven's sake... this inexpensive switcher was purchased back in July of 2003. Not bad for a sub $100 supply. It has powered an Icom 706, 7000 and 703. It also powered my FT991 and the current IC 7300 travel radio. It has been used in basement shacks, used and left in the rain at a back porch Florida rental. You name it and this supply has done it! I never detected any RF hash. Yes, it has a cooling fan but unless you're in a quiet room, it's of no consequence.

This little unit fits so well with my cabling, the travel case, etc. I just bought another one for $114.95, delivered! I sure don't understand the negative ads.

Thanks Martin and Merry Christmas!
_________________________________________
Just acquired this little supply to power my usually mobile IC-706MKII during a vacation to Myrtle Beach later next month. Today I tried it out backyard portable with the '706 and an MP1 antenna. My experience in this situation (i.e. with the MFJ 4103 supply and FT-817) is if the ACPS is producing hash either over the line or through the cabinet, the MP1 sitting 10-15 feet away will pick it up. I tried 20, 17, 15, 12 and 10 and could find no hash. I switched to a 17 AH gel cell as a reference and noticed no decrease in noise.

This supply does have an internal fan that runs all the time. Unlike an MFJ 4035MV I had a few years ago, the fan noise is not objectionable. It is a very soft, almost pleasant sound.

I did take a brief glance under the hood. Construction, soldering, etc. appear fine. So far, the MFJ 4125 has given me about 6 hours of reliable service. I think its a keeper.

73 de Bill / K8DXX
K4LRM Rating: 2022-08-11
Use IT Properly Time Owned: 0 to 3 months.
I'm disappointed as to the reasons for some of the negative reviews on this power supply. I purchased mine used, for $40 at a ham-fest. I use it for travel to power an IC7300. I have a 35A Astron with meters for the shack. I have an IC7600 and a Kenwood TS590SG in the shack. If you don't like the fan noise then move it away from you!
Purchase your power supplies to meet your different needs! I love how small, light, and reliable this power supply is for travel!
N4KVE Rating: 2022-04-26
Great so far. Time Owned: 0 to 3 months.
Got this from a SK who had it for years. He powered an Icom 207H with it. It seems to work fine, & the fan is NOT noisy. I’ve had to do the resistor mod on several Astron SS-30’s to reduce the wind noise, but it’s not necessary on this 4125. I use a big heavy Astron for HF, but for a PS on the go, this will be perfect. Looks well made inside.
KJ4KPW Rating: 2020-08-01
Spend more on something else. Too loud! Time Owned: more than 12 months.
I highly recommend not buying this power supply. I can't give it 1 star (wish I could) because it does supply power and does work.

But the fan noise is inexcusable, 100%. It is very loud and there is no reason for the lazy design.

You should spend just a little more money for literally anything else.

WB0AL Rating: 2020-04-10
Better than expected Time Owned: 3 to 6 months.
I bought this power supply for a new ham. His XYL made him get rid of his radios, so I took it back. I power my Yaesu FT-857D. It works better than expected. Absolutely no RF hash. Delivers 13.8 volts and slightly less when transmitting 100 watts. I do not understand why the fan noise is an issue. It is louder than most, but, not obnoxious. My version is the MFJ-4125P with Anderson Power Poles. That’s a nice touch. This PS is made in Taiwan, and is worth the price.
N7AG Rating: 2018-09-07
Good, but noisy Time Owned: 0 to 3 months.
This 4125P, cute little bugger, too bad any the fan whine. With longer as or dc cords, could be hidden in a quieter location.
N1XOI Rating: 2018-04-03
Good value, no frills, noisy fan Time Owned: 3 to 6 months.
Got one last December, to go with my new IC-7300.

Likes:
- Small and light
- Inexpensive
- Push-on 5A connectors in the back
- Decent quality PCB, assembly and component
- No detectable RF hash

Dislikes
- Fan noise
- Not detachable cord
- Voltage drop at high load

Reading reviews I was aware of the fan noise, but I had underestimated how annoying it can be over time... I wanted to wait for the warranty to expire before doing something about it, but after almost four months I could not stand it anymore.

To keep it simple I just added a resistor to the positive wire supplying the fan, as countless others have done. I built a simple extension to the original fan cable, with the negative being a pass-through and the positive having a few resistors in parallel for a total of 78 Ohm. That way the mod is easily reversible.

I tried with about 100 Ohm first. While I could barely hear the fan, the airflow seemed reduced too much. I found 78 Ohm to be a good trade off for me. Prior to the mod I measured to noise with a Sound Meter app. While not necessarily accurate in absolute terms, the relative difference between levels should be. After the mod I measured a reduction of more than 10dB at one foot from the front panel vs before the mod.

In my operating position I have the supply on a shelf underneath the table where my radios are. My ears are about three feet or so from the supply with the surface of the table in between but the shelf is open. At that distance now it sounds about the same as a desktop computer fan. Much better!

After the mod I tested the supply with an Agilent electronic load we have at work. Loaded it up to 20A for five minutes and the fan exhaust got warm but never really hot. The top of the case was also warm to the touch, but not even close to be alarming. I usually operate Digital Modes at QRP or low power level, so I do not expect any issues with the reduced airflow.

One thing I noticed is that under load the output voltage sags noticeably, although it remains stable at any given load. The set output was lowish to begin with, just below 13.7V, even at no load. Got down to about 13.4V at 20A. Others have reported only about 100mV drop at 20A or so. It might just be my unit with a bit worse load regulation. At any rate, nothing a typical transceiver cannot handle. For the price it seems a more than decent power supply. As I had the supply opened anyway, I adjusted up the supply voltage to 13.85V at no load. There is a trim pot in one of the upper corner of the vertical daughter board affixed to the main PCB.

Be aware that the schematic on the MFJ product page is not the right one. It is close enough but it is for one of the adjustable models, with Ammeter and Voltmeter on the front panel.

All in all a good value, wish the fan was thermostatically controlled with variable speed. Maybe this will be my next mod when I have more time.

We'll see about durability. I had a Samlex SEC 1223 smoke on me (bad capacitors) and those are at least 50% more expensive than the MFJ-4125. Hope to have better luck with this.
K3VA Rating: 2017-01-13
Compact/Reliable Time Owned: 3 to 6 months.
Used one time on a Dx/Vacation trip and
worked fine.
Fan is a bit noisy and the power cord is
not detachable for packing/travel use.

Also, the 5amp fuse is Internal and not
on the rear panel as the manual states.
WA0ZZG Rating: 2015-07-21
Quiet RF wise Time Owned: 0 to 3 months.
Picked up one at an estate sale, still in the box and plastic, for $70. It is very small and light. My meter shows 13.79V. No RFI problem. Who ever built this for MFJ uses the same design for Yaesu switchers. Plan on bypassing the 120/220 switch and using it for a Hi/Lo fan switch along with a 68 ohm resistor.
K0DOG Rating: 2015-04-29
Noisy Time Owned: more than 12 months.
In a weak moment (cheap moment) this power supply appealed to my cheap side.
Construction is robust enough.
Noise level is objectionable.
Absolutely would not buy one of these things again