[ARC5] M.C. Jones Micromatch 517B

[Mike Everette via ARC5]

Not sure exactly what frequency range the 517B is; but I can relate some experience with the Jones Micromatch in general.
I found a Jones unit at a hamfest years ago that sounds similar to what you have.  It was originally part of some military transmitter; and all I had was the pickup unit and the connectors that screwed onto the diode mounts, with cables cut off.  Back then I had access to a Jones catalog, and actually found mine listed.  It was for the 200-500 mc range if I remember right.  However, I discovered that it would work quite well even at HF.  I used a zero-center microammeter as an indicator, and again if I remember right, it was either 100-0-100 or 150-0-150 uA, and with a transmitter in the 75 to 100 watt range, even on 80 meters, the indication was quite good.  Of course I had a potentiometer in series with the meter to limit the current, and set the full-scale max reading; the value of the pot will be somewhat dependent on the meter's internal resistance but in general, a 50K will be all you'd need.
The Jones catalog is probably on line somewhere if you do some searching.
73
mike
WA4DLF

      From: Glen Zook via ARC5 <arc5 at mailman.qth.net>
 To: "kgordon2006 at frontier.com" <kgordon2006 at frontier.com>; Roy Morgan <k1lky68 at gmail.com> 
Cc: "ARC5 at mailman.qth.net" <ARC5 at mailman.qth.net> 
 Sent: Friday, May 15, 2015 4:02 PM
 Subject: Re: [ARC5] M.C. Jones Micromatch 517B
   
Instead of using 1N914 silicon diodes, use Schottky diodes.  Those work as well as Germanium diodes, sometimes better. Glen, K9STH

Website: http://k9sth.net
      From: Kenneth G. Gordon <kgordon2006 at frontier.com>
 To: Roy Morgan <k1lky68 at gmail.com> 
Cc: ARC5 at mailman.qth.net 
 Sent: Friday, May 15, 2015 11:31 AM
 Subject: Re: [ARC5] M.C. Jones Micromatch 517B
  
On 14 May 2015 at 17:45, Roy Morgan wrote:

> ARC-5- folks,
> 
> I have unearthed an M.C. Jones Micromatch 517B SWR meter.
> 
> It has N connectors and the usual controls:
> CALIBRATE
> FOR - BACK - CAL - VSWR
> and is marked 40 WATTS
> Watts scales 0-4 and 0-12
> SWR scale 1 to 100
> 
> The coupler is just over 3 inches long and has two 1N23B diodes.
> 
> I have tried the thing at HF - the needle does not budge
> With my 2 meter HT, the needle moves, but barely.
> 
> Is this thing meant for UHF?

Hi, Roy:

In my experience, the shorter the path between the two connectors, the 
higher the frequency for which such devices were designed....but not always.

Have you checked the resistors in it? There should be at least two identical 
ones and those would determine the impedance for which the device was 
designed.

Also, as I remember it, 1N23s were subject to deterioration such that over 
time they became nothing so much as resistors themselves.

But I could be wrong...

If that was mine, I think the first thing I would do, after checking the 
"impedance setting" resistors for value, would be to replace the 1N23s with 
something like 1N914s (silicon), or 1N34s or 1N91s (Ge) (if you can find 
them) even temporarily, then retest.

I have some NIB "radar" diodes around here somewhere which you could try 
too, if you wanted them. Those encapsulated jobs with the gold-plated ends 
on them.

  
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