V a c u u m T u b e

2 6 4 B V a c u u m T u b e

C l a s s i fi c a t i o n

The No. 264B Vacuum Tube is a three-element filament type tube for use as an audiofrequency amplifier in applications requiring a tube with low microphonic noise response in apparatus where high input resistance is necessary.

It replaces the No. 264A Vacuum Tube and is the same electrically and mechanically exceptthat it is equipped with a base employing silver plated contact studs.

B a s e a n d S o c k e t

The No. 264B Vacuum Tube employs a four-prong thrust-type base suitable for use in aWestern Electric No. 143A Vacuum Tube Socket which is equipped with silver plated contactsprings.

Rating and Characteristic DataFilament VoltageN o m i n a l F i l a m e n t C u r r e n t . . .Maximum Plate VoltageGrid VoltageAverage Plate CurrentAverage Plate Resistance.. ..Average Amplification FactorApproximate Direct Interelectrode Capacities

P l a t e t o G r i dP l a t e t o F i l a m e n tG r i d t o F i l a m e n t .

1.5 Volts, D.C.0.3 Ampere1 0 0 Vo l t s

- 7 . 0 Vo l t s2.6 Milliamperes

11,800 Ohms7 . 0 5

5 . 3 M M F2 . 2 M M F3 . 5 M M F

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Average Static CharacteristicsThe accompanjdng curves give the static characteristics of the No. 264B Vacuum Tube.

These curves have been obtained with the filament operating on direct current and the grid andplate returns connected to the negative filament terminal.

G e n e r a l F e a t u r e s

Due to the rigid construction and the short filament which has been designed to reducevibration to a minimum, the microphonic response of the No. 264B Vacuum Tube is very low.

The base prongs have been silver coated to eliminate contact noises which develop at theinterface between base prong and socket spring when both are of base metal.

Care in manufacture and also inspection tests insure a high input resistance.These features together with its low power consumption make this tube particularly suit

able for use in the early stages of high gain amplifiers.The rugged construction of the tube and ample electron emission supplied by the filament

operating at a low temperature, insure the maintenance of uniform electrical characteristicsthroughout a long life.

I S S U E 1

NOVEMBER 1 . 1934

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V a c u u m T u b e

Wes te rn E lec t r i c

2 6 4 B V a c u u m T u b e

Classif icat ion—Small, low-noise, f i lamentary tr iodeThe 264B tube replaces the 264A and is identical with it except that the base pins of the 264B

tube are silver-plated to minimize contact noise.

Application—Audio-frequency amplifier particularly where exceptionally low tube noise orexceptionally high input resistance are required.

Dimensions—Dimensions, outline diagrams of the tube and base, and the arrangement of theelectrode connections to the base terminals are given in Figures 1 and 2.

Base—Small, four-pin thrust type, with pins silver-plated.

Socket—Standard, four-contact type, preferably with contacts silver-plated, such as the WesternE lec t r i c 143B socke t .

Mounting Positions—The 264B tube may be mounted in any position.

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2 6 4 B

Average Direct Interelectrode CapacitancesG r i d t o p l a t e 5 . 3 fi fi f .G r i d t o fi l a m e n t 3 . 5 / x M f -P l a t e t o fi l a m e n t 2 . 2 / x / x f .

F i l a m e n t R a t i n g

F i l a m e n t c u r r e n t 0 . 3 0 0 a m p e r e , d . c .N o m i n a l fi l a m e n t v o l t a g e 1 . 5 v o l t s

The filament of this tube is designed to operate on a current basis and should be operated at asnear the rated current as is practicable.

Characteristics—Grid-plate characteristics of a typical 264B tube are shown in Figure 3 for severalvalues of plate voltage. Corresponding amplification factor, plate resistance, and transconductancecharacteristics are given in Figures 4, 5, and 6, respectively. Plate characteristics for several valuesof grid bias are shown in Figure 7. In each case, the grid and plate voltages are measured from thenegative end of the filament.

Operating Conditions and Output—Permissible grid and plate voltages are includedwithin the area, ABCD, in Figure 3. Values of amplification factor, plate resistance, and trans-conductance, and typical performance data are given in the table on page 3 for recommended andmaximum operating conditions represented by selected points within this area. Recommendedconditions or others of no greater severity should be selected in preference to maximum conditionswherever possible. The life of the tube at maximum operating conditions may be shorter than atthe recommended conditions.

The performance data include the fundamental power or voltage output and the second andthird harmonic levels for the indicated values of load resistance. The fundamental output is givenin terms of the power, Pm, in milliwatts, for values of load resistance, R, equal to and double thevalue of the plate resistance, rp, and in terms of the voltage, Ep , in peak volts, for values of loadresistance five times the plate resistance. The second and third harmonic levels, F2m and Fgm, aregiven in decibels below the fundamental in each case. The peak value of the sinusoidal inputvoltage, Egm, is numerically equal to the grid bias for each operating condition. For a smaller inputvoltage. Eg, the fundamental power and voltage output and the harmonic levels are given approximately by the following relations:

( 0F = E —■t^p -L-pm g

F2 = F2m + 20 logio

F3 = F3m + 40 logio T-

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V a c u u m T u b e

T a b l e

T r a n s - V o l tP l a t e P l a t e A m p l i P l a t e c o n - L o a d P o w e r a g eV o l t G r i d C u r fi c a t i o n R e s i s d u c - R e s i s O u t O u t

a g e B i a s r e n t F a c t o r t a n c e t a n c e t a n c e p u t p u tV o l t s V o l t s M i l l i - O h m s M i c r o - R M i l l i P e a k

a m p e r e s r p m h o s w a t t s V o l t s

R e c o m 6 0 - 2 . 0 2 . 3 5 7 . 3 11,700 6 2 0 I I 2 . 4

m e n d e d aI IP i 2 . 1

Operat R = 5rp 1 2

ing 9 0 - 7 . 0 1 . 9 0 7 . 2 12,800 5 6 0 R = rp 2 5C o n d i R = 2rp 2 3t i o n s R = 5rp 4 1

1 0 0 - 8 . 0 2 . 1 0 7 . 2 12,400 5 8 0 R = rp 3 3

R = 2rp 3 0I I 4 8

M a x i 9 0 - 5 . 5 2 . 8 0 7 . 2 11,300 6 4 0 R = rp 1 8m u m R = 2rp 1 6

Operat R = 5rp 3 3

ing 1 0 0 - 7 . 0 2 . 7 0 7 . 2 11,400 6 3 0 R = rp 2 8C o n d i R = 2rp 2 5t i o n s R=5rp 4 2

o n d T h i r d

Microphonic Noise—With a plate voltage of 100 volts, a grid bias of —8 volts, and a loadresistance of 100,000 ohms, the mean microphonic noise output level of the 264B tube measuredin a laboratory reference test set is 41 db below 1 volt. The range of levels of individual tubesextends from 30 to 52 db below 1 volt. Since microphonic noise level depends on the type andintensity of the mechanical disturbance which produces it, the values given here are useful chieflyfor comparison with the levels of other tubes which have been tested in the same way.

Fluctuation Noise—An irreducible minimum of noise in a vacuum tube is produced by uncontrollable, minute fluctuations in the rate of flow of electrons to the anode. With a plate voltageof 100 volts, a grid bias of —8 volts, and a load resistance of 100,000 ohms, the mean equivalentfluctuation noise input of the 264B tube for the audio-frequency range from 40 to 10,600 cyclesis 116 db below 1 volt. Individual 264B tubes may differ from this value by as much as 5 db. Byreducing the plate voltage to 26 volts and the grid bias to —0.5 volt, the mean fluctuation noiselevel may be reduced by about 4.5 db without seriously affecting the voltage amplification for smallsignals. The equivalent noise input voltage is equal to the measured output voltage divided bythe voltage amplification of the tube in the measuring circuit.

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A development of Bell Telephone Laboratories, Incorporated,the research laboratories of the American Telephone and Tele

graph Company, and the Western Electric CompanyV . T . D A T A S H E E T 2 6 4 B

I S S U E 1

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