The AM Forum

 Hello: I would like to replace my meter shunts in the RANGER II, dose anyone know of a good quality shunt, and where to purchase them?

Thanks: John W9BFO

Mouser and other suppliers sell 1% & 1/2% resistors or, if you have an accurate resistance meter, you can make your own with hookup wire and a wire table that lists wire gauge versus ohms/per foot or ohms per 1000 ft.

Or, click here: http://amfone.net/Amforum/index.php?action=search Put meter shunt in the Search Box and click Search. Lots of info

I carry different types of resistance wire if you want to wind your own. Plain copper wire is not temperature stable.

Carl

Let me guess.....  For winding parasitic suppressors, huh? :)


--Shane
KD6VXI

The original shunts - .51, 3, and 20 ohms were all 1/2w 5% resistors. There is really no reason to go to 1% unless you think you need the better accuracy. 1% resistors are expensive compared to 5% and probably not necessary.

I ordered new 5% values from Mouser - 1W instead of 1/2W

660-mox1ct52rrs1j  .51 ohm  (2) 
660-mox1c3roj        3 ohm
660-mo1cts2r200j   20 ohm

The 5% replacements, as long as they are new production and not carbon, should be OK although on general principle I prefer 1% for any sort of metering circuit.  But in this case the original meter movement isn't a high accuracy part anyway and one Ranger II I repaired had a meter movement that read almost 30% low.  Once you replace the resistors if there is a question of readings confirm with a known good external VOM or DMM.

Yes. They are relative meters at Best.  I have never seen one that was spot on.  Lots of people over or under load the transmitter. Or they dont realize the meter is reading a sum of currents.  The replaement 5% or fine.

During a recent amplifier revamp, I measured meters, resistors and voltages with three different VOM, VTVM and DVM delios.   Ended up taking averages with final say coming from the DVM if stuff was too wild.  

I found 1 ma. meters marked 50 ohms at 40, etc., but new resistors were well within spec. on the high impedance DVM and served to show which of my ohmeters were really accurate.  Surprisingly all within half and order of magnitude.   ;D  

 Stuff to ask yourself: Do springs get tired on D'Arv. meters?  Are printed scales really accurate, particularly at the low end or the range?  Linear or properly exponential?   Lots of things to play with.  Don't forget that high current measurement should really be with four leads, two current, two measurement.  The Johnson Ranger really didn't "care."    ...to say the least.

Trust nothing and measure everything until your comfortable with the accuracy limits of your instrumentation, especially if of 'ham' intended manufacture.

I also use nichrome wire wound on ceramic insulators for temporary power resistors.  Nice for dropping voltage on, say, a filament transformer to get a desired value at the tube sockets.  Then go buy a standard, closest value/wattage if desired.

Thanks to everone for the info and input, the resistors are ordered from mouser. These people are vey curtious and will work with you even on the smallest order.

John W9BFO

Yes, I find Mouser a good place to order. I don't know if it is new or not but my last order, which totaled well over $100, had the option of a $4.95 economy shipping charge. They UPS the order to your local post office and then a mail carrier delivers it to your home. I thought I would try it and see how long it takes. It does have tracking.

You expect me to start competing with RLM and Harbach in the voodoo science biz Shane?

All the stuff I got came from National and I wind my own shunts when needed like when I stuffed an 813 in a Globe Champ 300 and needed a new grid range. Wound a few for the Johnsons, Dentrons and other stuff that comes thru.

John,
When I did up my Ranger II many years ago, I order precision resistors from Mouser.  They were inexpensive and I ordered several values each side of nominal.  I then put my Beckman in series with the Johnson meter to dial it in so they read the same.  I realize that accuracy is not all that important, but since I was doing it, I figured why not make it accurate.  You can also start out on the high side and use a second resistor of higher value to bring it right on the money.  For the Ranger, I put the meter shunt in the cathode circuit since I operate the 6146 off the LV supply when driving my pair of 3-500Z's.  This allowed me to read the cathode current and got the meter shunt out of the HV path which is handy when you operate the final off the LV supply otherwise the meter does not measure anything! 

Joe, GMS     

Yes Joe, I agree and reading over the entries brought to mind this thought:
If precision resistors are available at the right value and wattage and are cheap, especially compared to what they use to cost,  then you almost have to use them. This eliminates one big variable in seeking some sort of precision in the nebulous realm of "ham equipment" measurement.