Introduction: Restoring a WW2 Era Multimeter to Working Order.
A number of years ago I acquired this early Simpson Electric multimeter for my collection. It came in a black leatherette case which was in excellent condition considering it's age. The US Patent Office patent date for the meter movement is 1936 and the batteries inside are dated 1944. The actual date of manufacture is sometime before 1944. The meter consists of a voltmeter (1000 ohms per volt) which has 6 ranges connected via jacks on the front panel with the highest range going up to 1000 volts. The current ranges are also connected via 4 jacks going from 1 mA to 100 mA. There also is a ohm meter which has six ranges which range from a R x 1 range to a 1 x 10,000 an additional range which is R divided by 5 range which is for measuring extra small resistances. The resistance ranges are switchable via the large switch on the front.
The voltmeter ranges work well and the current ranges also. The ohm meter doesn't work because the original batteries inside are dead. The five lowest ranges use a 1.5 volt battery and the highest range uses (3) 4.5 volt batteries. The 1.5 volt battery is of the still common "D" cell and the 4.5 volt batteries are of a package type which have 3 "C" cells in one package. I'm going to leave them in there for authenticity while bypassing it with a modern 12 volt battery of the A-23 type which is normally used in remote control key chains but will work fine here with a slightly lower voltage than 13.5 volts that the original batteries would've been.
1) (1) "D" cell, 1.5 volt.
2) (1) "A-23", 12 volt battery
3) Armor All Protectant
4) Electrical tape.
5) Hot melt glue and gun
6) Plastic Straw
7) Couple of tiny sheet steel pieces cut from a biscuit tin.
8) Soldering Iron and Solder
9) Long nosed Pliers
10) #2 Philips screwdriver
11) Tin snips
12) Paper scissors
13) Black and Red solid hookup wire 18 guage.
Step 1: Taking It Apart
Taking the meter apart, I was surprised to see the inside was very clean and had its original 3.5 volt batteries inside. One of them has July 1944 stamped on it. I really like the fancy graphics on these early Burgess batteries. Note in the picture that in these old meters they didn't use precision shunt resistors, they used coils wrapped with resistance wire. The white colored rheostat is used for adjusting the top of the scale for the resistance settings. There is also a "zeroing" screw on the meter face that adjusts the meter at the zero scale for better accuracy.
Step 2: Making a Battery Holder
Take the plastic straw and cut off a piece about 1 inch longer than the A-23 battery. Take your tin snips and cut 2 strips 1/4 inch wide x 1 inch long. Slit the straw lengthwise as straight as possible. Make a tight bend in both pieces of metal and shove the bent ends on each end of the straw so that they hold onto it tightly. Squeeze the ends of the metal pieces together with the straw between the pieces. Bend both pieces inside the straw so that they will touch against the ends of the battery and support it securely. The pieces that will touch the battery can each have a "V" bent into them horizontally to make a better connection with the battery. Secure each end of the metal pieces inside the straw with hot melt glue to give it a bit extra strength. Solder the black and white wires to the metal pieces with red for positive and black for negative. The battery holder can then be wrapped with electrical tape. Wire the new battery across the three old batteries but remove the old battery's + connection to the meter. The new battery would discharge across old batteries and not last very long. Since the 12 volt battery is only used for the 10,000 range it should last a long time if the disconnection of the old battery is done. The new A-23 battery can be secured inside with tape or left to hang loose inside the meter case.
Step 3: Wipe the Meter and Case Down With Armor All Protectant
The meter and case were clean but after being wiped down with Armor All Protectant they ended up looking almost like new. I tested out the meter on voltage, current and resistance scales and they were surprisingly accurate and needed no adjustments. I will now use this instrument to troubeshoot old gear as a technician would've done in WW2.