Radio Broadcast (May 1928-Apr 1929)

RADIO BROADCAST'S TUBE DATA CHARTS — IV CeCo MANUFACTURING COMPANY '"PHE chart on this page gives the characteristics of ■*■ the entire CeCo line of tubes. A glance will show that the line is complete, and that the constants are such as experience and engineering has dictated to be the best for the tubes serving the purposes for which they were made. In addition to tubes whose names and uses everyone knows, there are several others on this list that will need some explanation. For example, type G is a high-mu tube useful for resistanceand impedance-coupled amplifiers. Owing to its rather low plate resistance, 25,000 ohms at a plate potential of 60 volts and at zero grid bias, the tube will make a good detector. In addition to this tube, CeCo manufactures a special detector, type H, which has a somewhat lower mu and a lower Elate resistance than type G. Both of these tubes ave a fairly high mutual conductance. Type K is a special radio-frequency amplifier tube, with an amplification factor of 12.5 and a plate resistance of 11,000 ohms. Under normal operating conditions, viz, 90 volts on the plate and a negative bias of about one volt, the mutual con 500 3.0 100 <i 2.0 E 0 0 ' — RI nio DCA RAT0 Leo E — Ei 0A.O ) = 135 g=t>7 •a \ \ BROt ABO ST KY_ Rp\ l 1 \ >/\ A > / too.ooo 300.000 ioo.ooo heater-type tube operating as a C-bias or platerectification detector, and a microammetor in the plate circuit of the detector which acts as a vacuumtube voltmeter. The voltage ratio, Eo/ Ei, varies from about 40 at low broadcast frequencies to about 70 at 1500 kc. This means that an input voltage of 0.1 volt, after passing through the screengrid tube and its coupling transformer, became 4.0 volts on the input to the detector at 500 kc. and 7.0 volts at 1500 kc. Fig. C gives an idea of the selectivity of a single stage as illustrated in Fig. B. The primary of the transformer had an inductance of 350 microhenries, the secondary an inductance of 235 microhenries and the mutual inductance between them was about 160 microhenries, giving a coefficient of coupling of about 0.56. The secondary had a diameter of about 2 inches and was space wound so that its ductance is equal or better than the average generalpurpose tube, and naturally enough, a somewhat greater amplification at high frequencies results. Type L, 15 is a new power tube, as is Type L45. At the time of compiling these data, only experimental tubes were available, and it is not thought wise to include data on these tubes. Suffice to say, the CeCo organization is awake to the necessity of power tubes fitting into the picture somewhere -4 -3 -2 -1 0 +1 ■rZ +3 between the present 171 and the much more powerful tube, the 250 type. Despite the interest in the screen-grid tube, little has been done with it in commercial receivers, chiefly because it required a source of d.c. current for its filament. The chart below shows the characteristics of the CeCo a.c. screen-grid tube, the A.C. 22. It is a standard heater-type tube, namely, one requiring 2.5 volts and 1.75 amperes, and because of this construction it does not suffer from many of the faults of the d.c. screen-grid tube. It is not microphonic, its filament (cathode) is sturdy and it has copius emission of electrons. Its plate resistance is 450,000 ohms and its mutual conductance over 700 micromhos under normal operating conditions, i.e., 135 volts on the plate, 67.5 on the screen grid, and a negative bias of 1.5 volts on the control grid. Fig. A gives the essential characteristics of the tube plotted with reference to the control-grid bias. To see what the tube would do as a radio-frequency amplifier, the data in Fig. B and Fig. C were taken in the Laboratory. The circuit diagram is given on Fig. B and shows a resistance input of 3.5 ohms, a transformer coupling the A.C. 22 to a standard 7.0 ui 6.0 50 4.0 R \DI0 LAB CeC BRC ORA o A ADC roR\ ;.22 AST / / \ .1 /l // ' 1 1 1 c / i / 1 I / r 73 E \ 5 kc i=0.1. 290 K Ei:0 c 115 / / i / / / . \ V 10 7.5 50 2 5 0 2-5 5.0 K.C.OFF RESONANCE 7.5 10 resistance was quite low. The input resistance of the detector was high since it was an overbiased tube. As Fig. C shows, the selectivity of such a single stage varies at the two frequencies used. At 1290 kc. the selectivity is such that a 5000-cycle note would suffer a loss of about 3.5 db while at 735 kc. the loss would be 4.4 db. TEST CHARACTERISTICS OF CECO TUBES MODEL NO CORRESPONDING TYPE USE A BATTERY VOLTS FILAMENT VOLTS FILAMENT AMPERES DETECTOR PLATE VOLTS AMP.MAX. PLATE VOLTS GRID BIAS TEST DATA AVERAGE NOTES PLATE VOLTS GRID VOLTS PLATE CURRENT (mA.) PLATE RESISTANCE (OHMSX MUTUAL CONDUCTANCE MICROMHOS MU A OIA Detector Amplifier 6.0 5.0 0.25 45 135 0.5-9.0 90 4.5 3.1 9500 900 8.5 General Purpose OIB 201 B Detector Amplifier 6.0 5.0 0.125 45 135 0.5-9.0 90 4.5 3.1 9500 900 8.5 B-BX-C 199 Detector Amplifier 4.5 3.0 0.06 45 90 0.5-6.0 90 4.5 2.8 16,000 400 6.4 General Pur.3 Types of Bases RF22 222 R.F. Amplifier 4.5 3.3 0.132 180 -1.5/+45 135 -1.5/4-45 600,000 666 400 Special Circuits for 4 Element Tubes AC 22 222 R.F. Amplifier 2.5 1.75A.C. 180 -1.5/+75 180 -1.5/+75 4.0 400,000 1,050 420 E 120 Power Amplifier 4.5 3.0 0.12 135 15.0-22.5 90 16.5 4.0 7,500 440 3.3 Last A.F.Stage F 112 Power Amplifier 6.0 5.0 0.50 45 180 4.5-12.0 90 4.5 4.8 5,000 1,600 8.0 FI2A 112A Power Amplifier 6.0 5.0 0.25 45 180 4.5-12.0 90 4.5 4.8 5,000 1,600 8.0 G 240 Hi Mu 6.0 5.0 0.25 90 180 0.5-5.0 60 0 0.8 25,000 800 20 Res.and Impedance Amplifiers H Detector 6.0 5.0 0.25 67-90 1.5-4.5 80 0 3.0 14,000 1,030 14.4 Hard Detector J71 171 Output 6.0 5.0 0.50 180 16.0-45 90 16.5 9.0 2,500 1,200 3.0 Last A.F.Stage J 71 A 171A Output 6.0 5.0 0.25 180 16.0-45 90 16.5 90 2,500 1,200 3.0 K R.F. 6.0 5.0 0.25 45-90 135 0.5-3.0 80 0 4.8 11,000 1,130 12.5 Radio Frequency Amplifier L 10 210 Power Amplifier 8.0 7.5 1.25 425 12.0-35.0 180 12.0 7.0 7,000 1,100 7.8 Power Stage L 15 Power Amplifier 6.0 5.0 1.0 180 15.0 180 15.0 15.0 3,750 2,000 7.5 L45 Power Amplifier 2.5 1.5 AC. 250 -33 to-50 250 -50 32 1,300 1,845 3.5 L50 250 Power Amplifier 8.0 7.5 1.25 450 45-84 250 45 28 2,100 1,800 3.8 r " M-26 226 A.C. Amplifier 1.5 1.05 AX. 135 6.0-16.5 90 6.0 3.7 9,400 875 8.2 A.C.on Filament M-27 227 AC. Detector 2.5 1.75A.C. 45 135 6.0-13.5 90 6.0 3.0 11,300 725 8.2 Separate Heater A.C. R-80 280 Rectifier 5.0 2.0 350 125 R-81 281 Rectifier 7.5 1.25 750 110 Ad ver ti semen t # march, 1929 page 345 © Advertisement