shows the desiccant cartridge, the O- 
ring, and the receptacle as used on the 
phototube house. 
External "'C" Battery Unit and 
Associated Circuitry 
Many investigators as well as the 
manufacturer have resorted toanexter- 
nal "'C''battery supply. This permits the 
changing ofthe ''C''batteries without in- 
verting the instrument and removing the 
bottom plate. Additional modifications 
(fig. 4) which we have found advanta- 
geous are: (1) the inclusions of anextra 
"C' battery in series with Beckman bat- 
teries Nos. 3 and 4--this extra battery 
reduces the frequency of battery re- 
newal, (2) the inclusion of a four-posi- 
tion rotary switch which permits adjust- 
ment of the screen voltage without entry 
into the ''C'' battery unit, and (3) the in- 
clusion of another rotary switch (2-deck, 
1l-position) and a test meter outlet 
BATTERY 
CHARGER 
UNIT 
STORAGE 
BATTERY 
UNIT 
BECKMAN MODEL DU SPECTROPHOTOMETER 
|. 17V AC SUPPLY FOR BATTERY CHARGER 
2. BATTERY CHARGING AND/OR DC SUPPLY 
3.DC SUPPLY EXTENSION TO SPECTROPHOTOMETER 
4.DC SUPPLY TO TUNGSTEN LAMP’ 
5."C" BATTERY SUPPLY AND TERMINAL STRIP EXTENSION 
6. TEST METER FOR MONITORING TERM. STRIP VOLTAGE 
which permits the operator to check 
voltages on the terminal strip. 
A portable test meter has alsobeen 
constructed which facilitates the voltage 
measurements. This unit (fig. 4) has a 
reverse polarity switch, two volt me- 
ters, and an on-off push-button switch. 
These ''C'' battery and test meter 
units may be seenin figure 1 locatedad- 
jacent tothe phototube housing. The cir- 
cuitry is diagrammed in figures 3 and 4. 
The Battery Charger Unit 
For convenience the battery 
charger unit has been mounted along- 
side the spectrophotometer above the 
transmittance dial (fig. 1). This unit 
contains two conventional 6-volt trickle 
chargers with provision for charging 
two 6-volt storage batteries simul- 
taneously or independently, and a panel 
"C" BATTERY 
UNIT 
Figure 3.--Diagrammatic representation of Spectrophotometer modification. 
2 
