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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
W4KPA Rating: 2009-07-31
9 years and still great Time Owned: more than 12 months.
This is a nine-year update on this product. It continues to put out well-regulated, clean (no hash), 13.8 VDC power, and it does it reliably. I've never had the first issue with this power supply, and I've dragged on trips all over the U.S. and western Europe, operating it from 110 and 220 AC power mains. The fan in my power supply makes no noise -- none. In fact, before I wrote this review, I had to visually check it to make sure it was running. Maybe MFJ has changed fan suppliers in the nine years since I bought mine, but even if that's true, I'd consider that to be a minor issue. Put in a new fan if it bothers you. This little supply is clean, reliable, and durable. It's one of the better values out there.
VU2LID Rating: 2009-07-31
Good and reliable Time Owned: more than 12 months.
I took this supply to India (220VAC) after using it in USA (110VAC) for some time. It has been on continuously in India, 24x7 for more than 3 years. Even though we experience AC mains power interruptions often, MFJ-4125 has not developed any problems. I mainly use it for powering my remote station HF radio (reliability is very important in this case).

I have not yet found another reasonably priced switching power supply for Amateur Radio use which is as RF quiet as MFJ-4125 (most of the other high current switching power supplies generate severe RF noise).

Yes the fan is a bit loud, but other positive features and reliability of this supply makes it a great unit for use with an HF radio. Highly recommended !!
NJ6F Rating: 2009-04-19
4125 Is Great Time Owned: more than 12 months.
I have two of these units. Their fan pulls in the air that keeps it cool under (full load.)!!!
This is a perfect unit...small, light, runs on 220 as well.
When they say quiet, they mean free of radio noise / birdies.
I don't want to read another loud fan noise report again...are you hams or appliance operators.....put a lousy 100 ohm resistor on the red fan wire and get over it ...or make it a fancy temp sensing circuit like another ham had on his site.
You modified it under your own operating conditions for warranty purposes assuming you just draw maybe 7 amps on xmit every so often... 100 ohms keeps it low enough. Someone mentioned 50 ohms and it was still noticable so 100 ohms seems good for me. I leave my other one at full fan because I use the FT100-D Yaesu at 100 Watts along with running everything else off that one supply. I cannot hear it due to it being tucked away in a stereo cabinet.
Good job MFJ, and I like their MFJ-784 and 1025 as well.
W5AJ Rating: 2009-04-18
Poor Noise Time Owned: more than 12 months.
This is a great power supply for size, weight and performance. However MFJ mislead the public by calling it whisper quiet. I run a laptop in the shack (no desktop fan noise) and this is (was) by far the loudest item in the shack. It's disturbing and is no longer used in the shack, maybe field day or on DX trip. so for all it's worth the old Kenwood linear no fan supply is still the main supply over this noisey thing.
N1AL Rating: 2009-03-16
Very quiet with my fan controller Time Owned: more than 12 months.
I bought this supply because of
- Price.
- Low RF noise level.
- Small size and weight for portable operation.

To solve the fan noise issue, I have designed a fan controller that reduces the fan voltage for normal operation and increases it when the internal heat sink gets hot. See the article on my web page:
http://www.cds1.net/~n1al/ham/fan_controller.htm

With this modification the fan is nice and quiet for normal operation and runs over 7 degrees C cooler than before under continuous 20A load.

I use the MFJ-4125 with an Elecraft K3 transceiver and also occasionally as a bench 12V supply. I'm quite satisfied. The only reason I didn't give it a "5" is that I had to modify it to get rid of the fan noise.
N2UDW Rating: 2009-01-16
quit after plug in Time Owned: 0 to 3 months.
Bought 4125 with an HF package on ebay Plugged it in ,it worked for 1 min then failed. Put out 3volts. Mailed back to MFJ ,three weeks + later got a letter indicating I should call them. I called ... they could not give me an estimate on the phone for repair nor what went badly with supply. No data offered in letter or on phone. I said I would like an estimate on the repair and this request met with the response ... we'll call you back. I asked will the call back take another month? Answer ... we don't know. Disgusted, I gave them my credit card number and told them to fix it. Last MFJ product I purchase as repair department is slow chaos compounded by slower confusion.
KC0GLA Rating: 2009-01-10
Small and Light Time Owned: more than 12 months.
I bought this over 2 years ago. I used this on what was my main rig and for FD use. I did have one problem of the supply shutting down on my TT Jupiter under full power. I never did notice any RF hash from supply as long as the radio was grounded to a good ground. I have learned that most people are getting noise off of their AC power ground (most Astron supplies were not grounded thus no noise).

Positives very small, lightweight, 20 Amps, and 3 way binding posts plus accessory terminals. Negatives noisy fan, can be overloaded easier than other supplies.
KI6ILX Rating: 2009-01-09
Great with simple modification! Time Owned: more than 12 months.
I bought one of these little power supplies on the advice of a friend, and it worked fine, but I was amazed at how loud it was! How could so much noise come from such a tiny thing?
After about a year of hiding it under my desk, I decided to see what I could do about the noise. I opened up the case and disconnected the fan by pulling the small plastic connector from the PC board. After running it with the case off for a while, it was just barely warm (and totally silent!).
Running without the case is not acceptable or safe, so I drilled a whole mess of 1/4" holes in the top of the case for ventillation. It never gets even more than slightly warm, but I only transmit SSB, so I cannot be sure it wouldn't get warmer using other modes.
I can't imagine my mod does the warranty any good (!!!), but if the noise bugs you like it did me, then you might want to try this. The only problem I've had since drilling the case is that I sometimes leave the PS on for days. I now have a great little PS and you can too!
WA6MOW Rating: 2008-10-30
Reliable Product Time Owned: more than 12 months.
I own two of these little power supplies. Both have a different fan sound. I don't find the sound offensive. A simple solution for me is to keep the supply under my desk where the sound is not a factor. The 4125 has a small foot print and is a reliable inexpensive supply. They are readily available used for $75.00 or less. I think most of the MFJ products I own are a good value and very functional.
KB1PGH Rating: 2008-08-12
What`s up with the fan noise? Time Owned: 3 to 6 months.
The 4125 works great but the cooling fan is just too loud for any sort of indoor work.That fan is too distracting to make the product enjoyable.Let me put it this way.My wife in the other room said "Is that fan going to be on all the time?"Spend a few extra bucks and get yourself a Alinco DM-330.Now I finally have piece and quiet back into my life