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 to an exter- 

 nal "C" battery supply. This permits the 

 changing of the "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 an extra 

 "C" battery in series with Beckmanbat- 

 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, 

 11 -position) and a test meter outlet 



which permits the operator to check 

 voltages on the terminal strip. 



A portable test meter has alsobeen 

 constructed Avhich facilitates the voltage 

 measurements. This unit (fig. 4) has a 

 reverse polarity s^witch, two volt me- 

 ters, and an on-off push-button switch. 



These "C" battery and test meter 

 units may be seen in figure 1 located ad- 

 jacent to the phototube housing. The cir- 

 cuitry is diagrammed infigures 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 



3. 



Ill 



STORAGE 



BATTERY 



UNIT 



BATTERY 



CHARGER 



UNIT 



"C" BATTERY 

 UNIT 



BECKMAN MODEL DU SPECTROPHOTOMETER 



1. 117 V 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 



TEST 



METER 



UNIT 



Figure 3. --Diagrammatic representation of Spectrophotometer modification. 



2 



