Any opinions on this MFJ edge wound roller inductor?

[K1JJ]

On page 82 of the catalog look for the 404-1032 silver plated, edge wound roller inductor. Anyone have experience with it?  It looks like it should handle 1500 watts pep for my 8877 amp. Hard to say without seeing one.  I'm wondering if anyone has used one of their "big" Ameritron ATR-30 tuners that supposedly runs one of these.

Page 100 shows the ATR-30 tuner it's used in:

http://www.mfjenterprises.com/catalog/mfj/Full_Catalog.pdf


404-1032, $140.00. Flat wire, edge-wound,
high power air roller inductor. Silver plated
Cu coil, silver plate contact discs and contact
shaft. Heavy duty 1/4” thick fiberglass frame.
16 uH, 31 turns, 21/2” coil dia., 1/4” round
shaft, 3” shaft length. 23/4Wx31/8Hx8D”.
Used by Ameritron ATR-30, 3kW PEP SSB.

I'm surprised at all the RF amplifier building parts MFJ sells. They have glow bars, transformers, tubes and other assorted stuff. Prices seem reasonable for a commercial vender.

T

[K5UJ]

You can probably do a lot better by going to hamfests and/or sifting through eBay.  I got a nice Gates 10 amp roller inductor on eBay for under $100 once.  I'd trust it way more than anything new out there.   The new parts being made now probably (based on what I have seen) do not have the physical quality of the old buzzard stuff found in old broadcast rigs and phasors, the products of Johnson, Gates etc.   Kintronic makes roller inductors but they cost a fortune.   The only reason Ameritron, (MFJ) Ten Tec etc. use the new junk is because they have to have large quantities and the new junk is what's available if you need 1000 roller inductors.  If you only need one, you can look for quality in second hand parts. 

It still kills me that an outfit like PalStar wants over $1000 for a tuner but look inside and you see that you can do better with hamfest parts for a lot less.  If you are in a hurry you can go with a new one and look for a better used one later.  PEP doesn't mean anything with these parts.  Find out the current rating--for AM a 5 amp inductor is probably okay up to 300 or 400 watts (5x5 x 50 ohms = 1250 watts) but for a low Z or high power I'd want at least 10 A. 

Rob

[KL7OF]

Says"MFJ" on it....

[n1uvi]

The PEP 3KW SSB rating is a max input rating so be careful there
might handle 1000 watts FB but might flash over at 1500

[K1JJ]

Yeah, my thoughts too.

You can tell I'm desperate for one to be looking at MFJ.  

A friend said he had a roller - and I drove over there yesterday only to find it was a fixed inductor. Too bad.

Well, I'll keep looking around for a good quality older vintage. I used to have a few but sold them all - decided never to use a roller inductort again for a QRO amplifier. Plug in coils or bandswitched is all I do. But this is a unique situation needing variable L to find the IMD sweet spot.

Maybe someone here will take pity and say, "Hey, don't buy that MFJ.... for $100 you can have this FB 10A roller!"  

T

[WBear2GCR]

Maybe with some thin copper refrigeration tubing and a harbor freight or homebrew rolling rig you can homebrew ur own
roller inductor?

I'd think some schedule 60 PVC pipe, a lathe to make grooves, you could even lay the tubing in using the lathe
by hand... then all you need is some polycarbonate, or PVC sheet, etc to make ends, some rods to hold the thing
end-to-end and a shuttle assembly for the roller part... that might be the hardest part to fabricate... you can make it
a nice 4" diameter or so.

What do they use to connect the rotating inductor electrically?

 

[WBear2GCR]

fwiw, several candidates on epay right now... bigger and less expensive than the MFJ, it seems...

[WQ9E]

Just be cautious with used, if the surface is really pitted it will be a PITA to use.  The roller to rod contact should also be checked although it is probably easier to refurb if needed.  I have seen several at hamfests that were stored in lousy conditions and with a lot of cleaning and some of the silver bearing lube they will probably be usable but will never work like new.  I used Gates units to build both of my reversible L tuners and they came from hamfests but I passed on several before picking these up.  A roller inductor with flaky contacts is bad enough in an antenna tuner but is really flirting with disaster in an amp.  At least in the antenna tuner you can make the adjustments at reduced power.

I bought a big roller from SS of NE when I built my amp several years ago and at that point the price was pretty good but I don't see that model anymore and the similar ones are all over $400.

My biggest concern with the MFJ would be the roller to coil interface in terms of life over time.  I have used some of the MFJ RF stuff and it was fine but it is always nice to get a good look at it and they don't have really good photos in their catalog/on their site.

[K1JJ]

Thanks for the replies.

Well, a good engineer friend of mine suggested I not use the roller inductor for the higher power 8877 application because of the intended Hi-Q.  I plan to use up to Q=60.  The formula works that plate current times Q = circulating current in the tank.  So 1A   X  Q 50 = 50 amps.  That would cause most ham rollers to arc between the roller and coil causing severe splatter and pitting, etc. So the MFJ is certainly out.

So bottom line is I am OK using a roller at the 50 w level for the hi-Q 4CX-350FJ amp, (100ma X Q50 = 5A)  but maybe I should  stick with a bandswitch and fixed inductor for the 8877 amp. I can always tap the coil more finely and use a bigger bandswitch.  

If I did use a roller in the 8877, it would have to be a big MoFo to handle the current.

I got two emails from guys who have large rollers. Maybe a 25-50A unit will work.... we'll see what the pics look like and if they will fit in the cabinet - and go from there.


T

[W1RKW]

I was going to say Tom, reverse engineer it and see if the wire size can handle the voltages/currents experienced. Chances are it just rated for typical ham use, ie. 1500w SSB/ICAS.  Then again, maybe not.

Roll your own!  You do magic with metal.