B&K bk-650 Service Manual

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B&K MODEL

TUBE

TESTER

OFFICIAL INSTRUCTIONS

"A"

Circuit

The Model 650isa dynamicmutual conductance tube

in twochassis.The

of

the necessary voitages requiredtotest

sockets.

voltages required for the auxiliary socket panel appearonthe

contact conneetor locatedonthe bridge panel

this

lower-hand contact wouldbemarked

readings from bottom to Theleft

the

lower left-hand corner and read from bottomtotop,

These correspond to the The schematicdiagram allof the necessary voltagesto troubleshoot

this instrument. All voltages measured areopenedcircuit voltages

measured

been made with

ground.

With test switch in test

contact

the main panel sitting upside down and the meter closest to you,the

with this service information

with

115

a

first

chassis consistsof the main panel which contains

the tubes and all

.

aïe

numbers

in the followingmanner.

1

and would

row

of

on

contacts start with

the schematic diagram

read

.

V

AC

on

the primary, and measurements

ohm

per

# position

volt

.unless noted .

or

equivalenttochassis

tester,

33

The terminals of

-

#

1

11

to

#

test

#

11

built

in

,

I

The

tube

tester

winding of transformer between brown and red-green, and the

between red-yellow and

ohm resistors, and the two halves of the

The indicating meter connected with a shunting potentiometer which

the sensitivity control across the

The plateofthe tube under test connects to terminal

and2respectively whichisthe cathode

voltage

In

the test position, the cathode

voltages

heater selector switch .The bias

from terminals

tube. Injected in phase with the

us

conductance.

are

with the signal necessary to make themeasurement

series

upper

is

basicallyabalanced bridge circuit, consisting the

red,

and

resistors

two

is

required

power

between

,

that isobtained from pin

.

This

is

terminals

€or

or

8,

depending

the

winding the windingtoprovide

bias

is

R-5

and

ohm resistors.

83

in the

voltage

upon

a small signal

is

ground and the heater

3

the tube under

4,

and

the

biasclassificationofthe

#

are

10

test

in

,

matched

type

or

#

9

which

selected

is

83.

11

obtained

150

in test

is

a

volts.

by

the

in

is

1

MODEL650

I

CONTINUED

A

is required.The negativevoltageisobtained

The output of the seleniumrectifier goes through a bleeder resistor

network,

R-23in turn returns to the output point of a voltagesensitive bridge

consisting

This bridge in is The obtainedthrough this bridge circuit from the transformer is

in series with the voltage

It

and provideuswith the basisofmeasurement.

closer examinationofthe bias networkand signalvoltage network

is,

in

turn, connected to the secondaryofthe power

consistingof R

of two

in

series

is

this signal voltagewhich appearsonthe biasstringto excitethegrid

with a windingofthe heater transformer.

#

turn

55

-

12

,

bulbs and two 16

goestoR-3,a voltagedropping potentiometer which

on

FROM

,

R-21,

the bias string.

R-22

ohm

PAGE

through

resistors.

1

selenium rectifier

,

R

-

23.

2

SERVICE

MODEL 650

purpose of thevoltage sensitivebridge is

automatic line voltagecompensation feature that our instrument

It

operates in the followingmanner.

The voltagesensitivebridge

When the line voltagedrops the resistance of the bridge circuit decreases causing an increase in signal voltage. If we did not employthis voltage

sensitive we had an increase in line voltage, this would

an

increase in plate voltagetothe tube under test,anincrease in heater

voltageand an increase in signal voltage.

This would cause the test meter

should.

However, because of the voltage sensitivebridge and the manner

which

bridge bucks this increase by causingadecrease the voltage

applied to the tube under

This

voltagesand

as

voltage, and will causethe insturment to benomorethan about

its reading

it

is

operated,

decrease of signalvoltage offsetsthe increase

causes

it did if the tube were tested at

regulation wilt be maintained between

€or

this

for

the insturment meter to

wide of line voltage.

has

an

inversecurrent characteristic.

on

the

an

increaseinline voltage, the voltage sensitive

test.

115

volts.

to

read

approximatelythe same

limits

us

with the

to read higher than

of

other tube

-

125

volts

5%

result

of

off in

it

line

in

The design of socket isbased on the that numbers of

tubes

lumped and tested in onesocket.

For

variety, in approximatelythe same region of grid

bias.

This is about

for

With the auxiliary socket panel turned upside dowa and the terminal strip

locatedon the furtherest away, these terminal

These numbers correspond to the inter-chassis plug number

which were described with referencetothe bridge panel.

I ’

having

example, socket

ait

other sockets panel.

thesame basing and operatingconditions

9

which tests tubes of the7pin miniature

2.5

volts. This same approach was used in grouping

Page

be

strips

3

are numbered from

B&R

MODEL

CALIBRATION PROCEDURE

The calibration of Model 650insturmentisquitesimple and can be

explainedonthe accompanying procedure steps.

1.

SIGNAL

The

first

stepisto take an AC vacuum tube voltmeter, and with exactly

115

volts

of

ÂC

line voltage, adjust the AC signal atterminal

bridge panel to read exactly

This adjustment

directly beneath socket

This

control

this socket.

2.

With

a

20.000 ohm per volt voltmeter, connectfrom pin

is

60.

can

be reached with a screwdriver the keyway of

1.45

volts

by adjusting the signal

6

O

B

located

#

6 to ground

adjust the

With a voltage

3

should read approximately volts.

These voltages are predetermined by the valuesofthe bias

whitch

the event that the other

oneof the resistors in the bias stringashavingachange in value.

is

3.

BALANCE

The next procedureisto

from terminal

sensitivity control

If

the instrumentisout of balance, the meter will deflected either

upward or downwards, depending

instruments in for service mustbechecked in this manner.

If

the instrument

under the front panel sensitivity control.

Adjustment of this control will eneble you to restore the to

reading.

bias

control which is

of

2.5 volts at pin

are

5%

.

a

small control located next to the signal

test

by connecting

#

10

ofthe plug to ground, and set the

to

is

out

of

panel another small sensitivity control to the bracket directly

R-4

to

getareading of volts.

6,

7

should read 3.5 voltsand pin

two

voltages do not in, you can anticipate

pot.

the for balance, and this is

a

ohm

,

10

watt wire wound resistor

upon

the direction ofthe unbalance.

you find located underneath

its

zero

MODEL

650

CALIBRATION PROCEDURE

CONTINUED

4.

Sincethe grid emissiontest effectively measures extremely high resistances the sensitivityofthis test will very humidity. Loss

of senstivity will occur under low temperature, low humidity

conditionswhile an increase sensitivity occur under high

temperature.

Absolute sensitivity can be obtained by periodically adjusting

the gas sensitivitycontrol withnotube in thesocket, that the

readingjust fallstozero.

By checking

maintained. For nominal sensitivity of approximately meg

this

Connect a 20 megohm

With

test

switch in

on the

P4 3 control can be withascrewdriver through the keyway of

test

OP

GAS

adjustment periodically, this threshold point can

resistor

shorts

and"gas"position, adjust P-43for a reading of

meter.

FROM

between pin1of socket#9and

PAGE

GRID

with

ohm

4

temperature and

,

adjust as

meter

be

:

For

more sensitivegas test, adjust for higher reading.

For

less

sensitive gas test, adjust

5.

THE

Is

to

correctly.

STEP

the signal control R-3 that calibrated tubes read

THE CALIBRATION

for

lowed reading.

Page

5

MODEL 650

VOLTAGE CHART

readings

With

1

=o.

2

3

=Heater.

4

=Heater.

5

=

6

7

=

in

8

=

9

=

10

=

11

=

12

=

13

=

14

=

15

=

16

=

17=

19=

20

=

takenwith

a

115volt AC inputand testswitch

#

0

volts

a

1.45

-

2.5 DC-.

-

8.3

volts

V.T.V.M.

series.

205

volts DC.

205

volts

35

volts AC.

35

volts AC,

35

volts AC,

35

200

N.C.

AC,

volts AC.

a

1%

V.O.M.

voltsAC can be measured withanAC meter.

orV.O.M. with high capacity capacitor

Pos.

2

only.

Pos.

2 only.

Pos.

2 only.

Pos.

3

only.

o.

AC

Line.

AC Line.

with chassisasreferencepoint.

in

test position.

Page

6