A CURRENT STABILIZER FOR LABORATORY ELECTROLYTIC PROCESSES H. BRADFORD THOMPSON,' MARY JO BOEHMm2and MAX T. ROGERS Michigan State College, East Lansing, Michigan
Iiv M . ~ Y laboratory electrolyses, the chemist may wish to maintain a fairly st,eady current although the resistance of the system, and thus the necessary voltage, may vary widely or undergo rapid fluctuation. The circuit shovn, though not truly a constant-current supply, canmaintain currents of up to 400 miiliamperes to within a few per cent, even when voltage changes in excess of 100 volts are necessary. The unit is versat,ile, simple, and inexpensive, and thus should be useful in many college lahoratories. Our model could he reproduced for about $30. Current stability is obtained by taking advantage of the high plate resistance of a. pentode-type vacuum tube. The circuit employed is shown in the figure. The same result could be obtained, of course, using a high-voltage supply and a large dropping resistor; however, to obtain equivalent current stability the supply voltage would be from 1000 to 2000 volts and the dropping resistors would have to dissipate up to 300 watts. In contrast, our unit operates at maximum values of 300 volts and 120 watts. The voltage-doubler pourer circuit operates directly from the power line. If one terminal of the load is to be a t ground potential, it will thus be necessary to insert t,he power plug "right side up," with the proper terminal to the ground side of the line. At some extra cost, this situation could be remedied by using a oneto-one isolation transformer. For maximum current, four type-1614 tubes are used in parallel. At currents up to 320 milliamperes the cheaper type-6L6 tubes could be substituted. Under 80 milliamperes somewhat steadier operation is obtained by removing all but one tube. At low currents (10 milliamperes or less) a single, low-power tube such as a 6G6, 6F6, or 6V6 gives slightly improved control. This substitution may be made without circuit alteration, as base connections on the tubes mentioned are eauivalent. 'Present address: Gustavus Adolphus College, St. Peter, Minnesota. Pre~entaddress: Metdlurgy Division, U. S. Naval Researoh I,ahorat,ory, Washington 25, D. C.
Tubes may be 1614,6L6, 6FG,6G6 or 6K6.
In three different laboratory applications this instrument has performed very well. Response to resistance changes is for practical purposes instantaneous. and the current stability achieved frees the operator of the task of constant adjustment of supply voltage. ACKNOWLEDGMENT
The authors wish to acknowledge the support of the Office of Naval Research through contract Konr 02300, NR 057222. Performance of Current Stabilizer Circuit
Single 6F6 tube, set for six milliamperes
Load
Load
Load
?esislane~, ohms
vollage, volla
cwral,
C-1000 1500
0-6 9.2 30 59
5000
10,000 15.1111ll
Four parallel 1614 tubes, set far 300 milliamperes
R7
milliamperes
6.2 6.1
6.0 5.9 F, R
