Handbook for Sound Engineers

Tubes, Discrete Solid State Devices, and Integrated Circuits 317

F 4 is used to find the power output

(12-20)

(12-21)

In the example:

F 5 is used to find the transconductance where

(12-22)

(12-23)

In the example,

The foregoing method of converting for voltages
other than those originally specified may be used for
triodes, tetrodes, pentodes, and beam-power tubes,
provided the plate and grid 1 and grid 2 voltages are
changed simultaneously by the same factor. This will
apply to any class of tube operation, such as class A,
AB 1 , AB 2 , B, or C. Although this method of conversion
is quite satisfactory in most instances, the error will be
increased as the conversion factor departs from unity.

The most satisfactory region of operation will be

between 0.7 and 2.0. When the factor falls outside this

region, the accuracy of operation is reduced.

12.1.15 Tube Heater

The data sheets of tube manufacturers generally contain

a warning that the heater voltage should be maintained

within ±10% of the rated voltage. As a rule, this warning

is taken lightly, and little attention is paid to heater

voltage variations, which have a pronounced effect on

the tube characteristics. Internal noise is the greatest

offender. Because of heater-voltage variation, emission

life is shortened, electrical leakage between elements is

increased, heater-to-cathode leakage is increased, and

grid current is caused to flow. Thus, the life of the tube

is decreased with an increase of internal noise.

12.2 Discrete Solid-State Devices

12.2.1 Semiconductors

Conduction in solids was first observed by Munck and

Henry in 1835 and later in 1874 by Braum. In 1905,

Col. Dunwoody invented the crystal detector used in the

detection of electromagnetic waves. It consisted of a bar

of silicon carbide or carborundum held between two

contacts. However, in 1903, Pickard filed a patent appli-

cation for a crystal detector in which a fine wire was

placed in contact with the silicon. This was the first

mention of a silicon rectifier and was the forerunner of

the present-day silicon rectifier. Later, other minerals

such as galena (lead sulfide) were employed as detec-

tors. During World War II, intensive research was

conducted to improve crystal detectors used for micro-

wave radar equipment. As a result of this research, the

original point-contact transistor was invented at the Bell

Telephone Laboratories in 1948.

A semiconductor is an electronic device whose main

functioning part is made from materials, such as germa-

nium and silicon, whose conductivity ranges between

that of a conductor and an insulator.

Germanium is a rare metal discovered by Winkler in

Saxony, Germany, in 1896. Germanium is a by-product

of zinc mining. Germanium crystals are grown from

germanium dioxide powder. Germanium in its purest

state behaves much like an insulator because it has very

few electrical charge carriers. The conductivity of

germanium may be increased by the addition of small

amounts of an impurity.

F 3 0.720

0.610

-------------=

=1.18

rp=1.18u52,000

=61,360:

RL=1.18u 5000

= 5900 :

F 4 =F 1 F 2

Power output=F 4 uold power output

F 4 =0.72u0.610

=0.439

Power output=0.439u4.5

=1.97 W

F 5 1

F 3

----- -=

transconductance=F 5 uold transconductance

F 5 1

1.18

----------=

=0.847

transconductance=0.847u 4100

= 3472 mho or Sμμ