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The GE Test Sets
Yes, you can tune up a radio with just a VOM, but after you get a chance to use a real GE test set (or look over someone's shoulder as they use one) you will want one. The same test set (with different cable kits, see below) can be used on MASTR IIs, Exec IIs, Execs, MVPs, MASTR Pros, Deltas, RANGRs, PortaMobiles, and several other radio series.

   
The 4EX3A11 test set
Click on this link to go to another web page that includes additional photos, including larger versions of the above.
A square-connector (MVP and MASTR II) microphone plugs into the left side of the test set, and the older round connector microphone plugs into the right side, as does the test cable to the radio. If you will be doing a lot of radio tuneup work it may prove valuable to hunt down a round mic connector and connect a foot switch with a 5 to 6 foot cable across the PTT and ground pins. You can have a MASTR II mic plugged into the square connector and the foot switch can be used to control the PTT leaving both hands free to twist the tuning tool and work the oscilloscope.

If you are only going to test MASTR II, MASTR Executive II, or Custom MVP radios, then you can use the 4EX8K12 test set kit (LBI-4436) which came in a smaller box and with permanently-attached red and black test cables.

The meter circuitry in the 4EX8K12 is identical to the meter circuitry in the 4EX3A10 or 4EX3A11. Eventually the red PTT button on either test set wears out and will need replacing. One common mod (while you have the housing open) is to add a SPST mini-toggle wired in parallel with the button. This allows you to use the red button for momentary PTT, and the switch when you want to key the transmitter for longer periods or when you need use both hands for something else.


A photo of the assembled 4EX8K11 test set.
A 4-pin round-connector-style microphone plugs into the microphone jack.
 
A photo of the assembled 4EX8K12 test set.
A square-connector (MVP-style) microphone plugs into the microphone jack.
Both of the above photos are thumbnails, click on them for a larger view.

Both the Model 4EX3A10 test set (LBI-3491E) and the 4EX3A11 test set (LBI-4454B) have a connector on the side for the radio-specific cables.

The three links in the text above will download the manuals for the 4EX3A10, 4EX3A11 and 4EX8K12 test sets.

Additionally, here are the schematics for the 4EX3A10 and 4EX3A11 metering cables for various radios:
PortaMobile, MASTR Pro and Exec     74 kB
MASTR II, Exec II and MVP     68 kB
Delta mobile     84 kB
Metering cables parts list    40 kB
With the information from the above LBIs you could design a 4EX3A10 and 4EX3A11 metering cable for almost any radio... even a MICOR.

All three test sets used a specially made analog meter calibrated as a negative 1/2 volt to positive 3 volt movement, and the entire meter box was configured as a 20,000 ohms-per-volt voltmeter. There are two good reasons for this:
1) ALL of the metering points on radios of that era were configured to use a 20k-ohms-per-volt meter, and the measurement circuit uses the input resistance of the test meter as part of a series circuit. Without a load of the correct value none of the metering readings were meaningful.
2) There were no inexpensive portable DVMs when these radios were being designed - every two-way tech had a portable VOM (a Simpson 260, a Triplett 630 or the WW2 surplus military equivalent), and all were 20K-ohms-per-volt. Modern DVMs have an input impedance that ranges from 2 to 11 megohms (depending on the manufacturer and model; most are 11 meg) and without the proper 20k-ohms-per-volt load none of the book measurement values will be correct.

In other words, YOU CANNOT USE A MODERN DVM TO PROPERLY TUNE A PRO, EXEC, EXEC II or MASTR II.

Two additional "gotchas" are that most inexpensive DVMs go crazy in the presence of RF energy due to the fact that they are sold by price, so to make a profit the manufacturers scrimp on the shielding, and lastly, in every case you are tuning for a peak or a dip - attempting to do that with dancing numbers on a DVM is an exercise in frustration - you are constantly trying to determine if the new number is higher or lower than the last number and your brain can't keep up with the DVM display update rate. You NEED an analog needle meter to see the peak or dip (and some of the peaks and dips are way too small).

I received an email that disagrees:

I don't agree, in fact it's much easier for me to use my Fluke DMM to detect some of the very small meter peaks and dips. There is no rule or requirement the metering points have to be loaded by a 50uA movement.

Erratic metering with low cost Digital Multi Meters is probably the result of the price you paid.

"If it's a good meter, it must be a Fluke".
Interesting - My main portable DMM is a Fluke 73. But he makes a good point. Next time I'll use the DMM in parallel with the test set and try it.

Other GE Test Sets

A photo of the assembled 4EX9A10 test set

GE made a number of purpose-specific test sets. One of them is the above 4EX9A10 multi-frequency IF generator. Does anybody have the documentation for it (LBI-4129)? We'd like to scan it and PDF it, as well as the docs on any other similar equipment.

Tuning Tools

A while back there was a question on the GE MASTR II mailing list about which tuning tool(s) were the best for working on MASTR IIs and MVPs. Eric Lemmon WB6FLY responded with: "All of the tuning adjustments on the MASTR II are handled by the MICOR "Universal Tuning Tool" part number 6684387C01, priced at about $5.50 (in early 2007) from Motorola Parts. This handy tool has a thin steel blade on one end that mates with the ICOM and front-end capacitors, and both 0.075" and 0.100" hex drives on the other end. Most coils on MASTR II radios require the 0.075" tool, but a few coils on the RF assembly require the 0.100" tool. The body of the MICOR tuning tool is large enough to get a good grip, making it easy to make very small adjustments. Overall, it's a must-have tool !"
Personally, I add a flap of tape right next to the handle. It makes counting turns much easier, plus it keeps the tool from rolling off the bench.
Update: an email to repeater builder advised us that two tools were purchased in early May of 2009 and cost US$19.82 (including shipping).


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This page split from the GE Index page 19-Jul-2012.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.