MFJ-250 Dummy Load... Unboxing And Review.

I need a dummy load for my HFamplifier project so I bought an MFJ250. What's it like...

[@douglaswilliams6834]

Just got one. The instructions are printed right on the can. No, you do not fill it 3/4 with oil. You fill the can with oil to within 3/4 of an inch from the top.

[@jlastre]

MA=Massachusetts; MS=Mississippi. I was told by the instructor of the ham classes run by the local ham club here in Peoria, IL (Illinios) that one could make a dummy load like MFJ does. But it seemed a bit of a pita as I don’t have a soldering iron. So I bought one of their dry loads which I’m still awaiting. Glad I did. Most of their loads are supposed to by within 5 or 3%.

[@bigchew3149]

Yes You Can I have made several over the years for myself & i even sold quit a fuw to friends from the radio back in the day ! They Are Very Easy To Make...But I Also Never New any one that needed a set of instructions to poor 1gal of oil into a 1gal can Either..lol.

[@craxd1]

They have the same problem with this as they do with their dry loads. The Heathkit did use a piece of round aluminum tubing, making it resemble a coaxial section. You might try adding some capacitance to ground, at the jack inside the can, to tune that out of it. It will be a small amount, somewhere around 30 pF.

[@KG4JYS]

You sure you didn't get a used one? Mine came much better packaged and had no dents or imperfections on the lid or anywhere else. MFJ doesn't include printed instructions with their products anymore. You have to download them in PDF and you can view or print at your leisure.

[@alanhughes1262]

Thinking of making one with short piece of 6inch steel pipe but cant seem to find a 50 ohm 200 watt non inductive resistor , i will fill it with paraffin oil .

[@mx1209]

Always a bummer when it's scratched or dented on arrival. Function over form though, right!? Thanks for the review.

[@markstump7079]

Anyone have a link to replacement oil, MFJ wants 50$ which is crazy.

[@michaelnobibux2886]

Mississippi !!!!

[@davecolver7769]

1. It's a paint tin. 2. The instructions are on the can.

[@Budro4764]

From Mississippi on trucks , planes , Boats then trucks again.... All that handling is rough on packages, i'm surprised that lid is in that good of a shape...

[@moussaelkarakizi2922]

i have a similar unit Steve, is only good to 60MHz. i wish you had a better view of the resistor, i hope is carbon based.

[@vk6cs456]

+Moussa El Karakizi Hi Moussa. I haven't checked but it's bound to be a carbon resistor. Up to 60MHz is still pretty useful, most high power amplifiers are built for HF/6m.

[@moussaelkarakizi2922]

+VK6CS , Steve, "60MHz", i was referring to the Revex SWR unit, is writing under the Revex logo in small print, reinforcing your conclusion on the 2m/70cm SWR dummy load reading..

[@vk6cs456]

+Moussa El Karakizi Aha... ok Moussa, got it , thanks.

[@billn3ry662]

Do you own a rubber mallet to carefully put the top on?

[@vk6cs456]

Yes, I have lots of rubber tools. The wire cutters take a while to get through anything.

[@sikes185]

Let’s try Mississippi

[@billn3ry662]

Very frustrating and tedious. ..You remind me of an individual I was training in the Learjet 55 if we waited for him to "sort it out" we would still be training him...

[@vk6cs456]

Watching isn't compulsory Bill.

[@beachsandinspector]

livinf in a PO box must be cramped some what.. how do you manage to live in there ?

[@vk6cs456]

+BeachSandInspector Technologies I read Dr Who's pamphlet... it's much bigger on the inside.

[@mauriciomagnovska8840]

how many watts is that resistor?

[@vk6cs456]

I'm not sure about the resistor but the load is rated to around 1KW.

[@MM0IMC]

I think it's a 200W resistor, the oil bath is the key. I have the Vectronics VEC-554 version WITH instructions. 😉 I use vegetable oil with mine. It says 1kW continuous for 10mins, yet the sticker on the can says 1500W continuous for 5 mins. Your mileage may vary. 😉

[@moderndaydad8654]

This basically a Bagdad battery

[@rufus4779]

MS = Mississippi A small country town where the grass still grows slow, young people say yes sir and no sir.

[@vk6cs456]

Good heavens... thanks Rufus.

[@hymlog]

...SO...WORKING ON A RADIO I CAN SEE THIS USEFUL ...BUT. WHAT USE IS IT FOR SWR READINGS? ...THAT CAN IS NOT YOUR ANTENNA!

[@vk6cs456]

Why the shouting? This is the first time the dummy load has been used. As it is an MFJ product I thought it would be a good idea to check the response against the specifications. This requires measuring the DC resistance and applying RF with an analyser or radio over the frequency range that I will be using, and checking the SWR. This ensures it complies with its specifications and it's an effective 50 Ohm load over the entire frequency range before I start using it for testing. Simple really.

[@hymlog]

...I don't hear a thing!!

[@vk6cs456]

Using capitals when writing a comment is shouting. And so is using an exclamation mark!!! The more exclamation marks the louder the shouting. So, do you get it? You should always test a new dummy load before using it.

[@hymlog]

...NOP!!!!

[@vk6cs456]

Now I get your Avatar.

[@sinkosav]

sorry,but that load will not survive long with gs35

[@vk6cs456]

+sinkosav I'll be delighted if the amplifier produces enough power to fry it.

[@vk6cs456]

This is ok for what I have in mind, but I had a HeathKit Cantenna back in the UK which was much better. This has a 2+ SWR on 70cm, the HeathKit was pretty flat from memory. Is the load you're making HF only?

[@michaelnobibux2886]

Just buy the resistor and build your own!! In an older ARRL handbook (perhaps 1988 ),a logarithmically shaped shell around the resistor is described that will extend the frequency range to low UHF.

[@wendellporter4810]

@@michaelnobibux2886 i built my own not too long ago based on the heathkit hn-31 cantenna as i service and test alot of hf rigs

[@jeromegrzelak8236]

draffffff

[@vk6cs456]

???

[@educatedmanholecoverbyrich8890]

I know what an empty can looks like, I know what the lid looks like. We are not 3 year old kid. Get on with it, for fuck sake.

[@vk6cs456]

Get a grip Tony... it's only amateur radio. Thanks for watching all the way through to the inside of the can.

[@FlattyDaz]

Tosser