Weston 686 TYPE 10A Instructions Manual

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INSTRUCTIONS

FOR

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WESTON

MODEL686 - TYPElOA

.True Mutual Conductance

Vacuum Tube Analyzer

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WESTON ELECTRICALINSTRUMENT CORPORATION

NEWARK5, NEW JERSEY,U. S. A.

Pri"ted in U.S.A.

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INSTRUCTIONS

FOR

WESTON

MODEL 686 - TYPE lOA

True Mutual Conductance Vacuum

Tube Analyzer

*

CONTENTS PAGE

Controls, Variable

Control Grid Voltage AdjusteL_mmm m_umm_m4
Heater Voltage Adjusterm_uhm_mmum_m__uu__m___A

Hum mmmmm_u__u__um___m__umm 5, 7 (Step27)

Plate Voltage Adjuster:

See "D-C Power Supply Controls"mm u m_5

Screen Voltage Adjuster:

See "D-C Power Supply Controls"m_mmm__m_m5

Self- Bias Resistance
Signal Amplitude AdjusteL_m__uuuum_5, 8 (Step 29)

Suppressor Voltage Adjuster:-

See "D-C Power Supply Controls"m__m__m__mu__5

D-C Power Supply Controls_m_m_mmmmm m__5

Detailed Description of Model 686 Type 10A__3-4-5-6

Front Panel View of Model 686 Type 10Am_mmmm__2

General Description m m___n__m_m mm_3
General Information __nm__mm__h__mum_mm_mmmm_

Gm Readings

Amplifier Tubes __hu mm___mm__u__mnm__mm_m7-8

Inconsistent on Filament Types:

See "Hum Control" _mm___mmm_mmu5, 7 (Step 27)
Low Gm Indications_muum__mumumm___m_m_hu 11
No G.mIndications_mm_m_mmmmm__mmmummuu 11

Grid Current _mmmm m_m_mm_m3, 7 (Step 28), 10
Helpful Suggestions in Tube Testinguhuum__h_uhum_1 0

Instruction Book um_mm_m__m m_m m h 10

Maintenance uhm_m m_m_m_mum_m_h__mmum

Meters

Control Grid Voltageu n__n mn_m__n nu4

Element Current _m m_m__m___m__mm m4

Element Voltage u umu__m mm 4

Gm (Mutual Conductance} m uu m___3

Grid Current __ 00__m__ um m__m ________00_3

Heater Voltage mmmmm_m_mmm m_mm__mm_h__4

Operation

Line Connections for 230 Voltsm___un__m__m_m m_6

Step-By Step Test Procedure__um__mm_un_m6-7-8-9
Theory of Operation_m_mm_m mumumm_ 9-10

00 ___ _ 00 _00 __ _ _m __ _ __ __ _ _ _ _00 __ _m___5

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CONTENTS

Order of Adjustment of Element Potentiometersmmm_5
Ordering Information _u__mm__mm mmm__m__m

Precautions __u__h__mm_mm_m_h mm_mm_umm m 11

PAGE

11

Switches, Rotary

"Control Grid" (bias} mmm m_m___m_m_-4

"Heater Voltage" u__m__mm__mm_m_nnm__m_mm_mA
"Gm Ra nge" _00 0000000000

"Element Current" mm mnm__m_m_mmmm__m_m__A

"Element Current Range"m__m__mmmmmmmm_m_A
"Element Voltage" ummm_mm mm_m_m_m__mu4

"Element Voltage Rang,e" __mmmmm hum_m___mA

Switches, Toggle

"Gm Reading" __nm um m_m m__m 6
"H eater Supply" 00 0000 0000___000000

"Gm Factor" n nn ~ 3

"Lamp Test' 00 00 000000___ ___00 000000 6

"Microamperes" u__m_uum m__mm_m__umm 3

"Plate 1- Plate 2" uu__mm_mmm__mn m__um___uu5

"Plate Su pply" nu m__m m m6

"Signal Cal." 00000000 00 000000 0000 00___6

"Supp" (Pos-Neg) mmm umm umm__6

Tube Manuals m_m_mmnmm__m_m__m mmmmm

Tube Reject Limits mm mum mu m__n m___m_ 10

Tube Testing

Ampl ifiers

Converters & Mixer Oscillatorsm_mm__m_h mm__8

Diode Detectors ___mnum_m___m m m_mm8

Rectifie rs _ __ __ __ _ _ __ 00_ _ ____ _ _ __ __ _ _ ___ __ ____ __ _ _ _ ___ 00 __ _ _00 __ _ 00 8

Thyratro n s __ __ _ __ __ _ __ __ _ __ _ _ __ __ _ __ __ _ __ __ _ __ _ ___ __ __ _ __ _ - - - - - - - - - - - - 8-9

_____u__m_mu 00_m__ ___u_m__ umu_ __ ___um _6-7-8

Voltage Regulators hu__mm__mmuu nmm_mm__mn9 '

Wiring Diagram of Model 686 Type 1OAu__m_humm12

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Front Panel View of Model686 - Type lOA

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INSTRUCTIONSFOR MODEL 686- TYPE lOA

TRUE MUTUAL CONDUCTANCE VACUUM TUBE ANALYZER

GENERALDESCRIPTION

The Model 686 is a complete direct reading True
Mutual Conductance Vacuum Tube Analyzer de-
signed to operate from any 105 to 125 or 230 volt
50-60 cycle outlet. It has eight mutual conductance
ranges with full scale readings of 300, 600, 1500 and

3,000 micromhos and also 3,000, 6,000, 15,000 and
30,000 micromhos. Instruments are provided for ac-

curately measuring all electrode voltages and for
reading electrode currents including minute grid

currents.

Internal power supplies and a signal source provide
all necessary potentials to panel controls, wherein
adjustments can be made in accordance with meter
readings. Tube sockets for all commercial type re-
ceiving tubes are mounted on a removable socket
panel across the top front section of the equipment.
These in turn connect through short-test switches to
patch cord jacks which are marked with R.M.A. pin
numbers and are used with patch cords for any or
all electrode connections. Thus with complete con-
nector flexibility and complete voltage control, all
kinds of static characteristics can be plotted, in addi-
tion to the measurement of Gill under any or all ap-
plied potential conditions.

DETAILEDDESCRIPTIONOF EQUIPMENT

THEG./IIMETER:The fan shaped instrument in the top
center of the main panel is the Gillmeter. The scale
is calibrated in two arcs reading zero to fifteen and

zero to thirty and sixty. This meter operates with
two multiplier switches marked "GM RANGE" and

"GM Factor".

should be kept small to avoid second-order effects.
The low signal voltages available make it possible
to measure all low bias tubes operated and tested
as Class A amplifiers.

It is advisable for the operator to select the low-
est grid signal voltage that will render reasonable
pointer deflection when testing all low bias high mu

tubes.

Note that a 3,000 micromho range is available with
either a 1 volt signal or a 0.1 volt signal. Use the

0.1 volt signal for low bias high mu tubes. The 1 volt
signal is useful for tubes having a-c operated filia-
mentary cathodes, where it is desirable to increase
the signal voltage to minimize hum effects.

The a-c grid signal voltage is calibrated on the
Gill meter to eliminate possible errors due to temper-
ature and amplifier gain. If the instrument is reading
the a-c plate current component 2% low because of
these effects, it will likewise require a signal voltage
2% higher in value to bring the meter to top mark
on Signal Calibrate. Since the signal voltage is
higher, the GIll indication will also be higher and
hence compensation is obtained.

GRIDCURRENTMETER:A two range microammeter

for grid current readings is mounted to the left of the
Gill meter. This instrument has a range of 15-0-15
microamperes. Readings down to and including one-
half microampere are easily read. The meter is nor-
mally shunted to 1500-0-1500 microamperes and is
switched to the low range by manipulation of a mo-
mentary toggle switch located to the right of the

meter.

The Gill Range switch is used for selecting the
300,600, 1500,or 3,000 micromhos range as required,
with corresponding grid signal voltages of 1.0, 0.5,

0.2, and 0.1 volts respectively. The GIllFactor switch
is used to extend the ranges by a factor of ten times
so that ranges of 3,000, 6,000, 15,000 and 30,000 are

also available.

On low mu tubes with low plate resistance, the
meter resistance is a reasonable part of the total tube
and tube tester plate circuit impedance; measure-

ments on these tubes would be in error unless .this

was taken into consideration. The compensation is
made automatically for all tubes having a plate

resistance above 250 ohms.

On high mu tubes the peak value of the grid signal

. voltage should be kept smaller than the dc grid bias

voltage to prevent direct grid conduction. On tubes

having sharply curved characteristics the grid signal

The meter is a zero center instrument to indicate

any or all components of grid current resulting from
gas, leakage resistance, or secondary emission. Grid
current readings are especially important in segre-
gating defective power tubes such as the type 6L6
where a limit of 3 microamperes is specified.

In taking grid current readings, the operator will

note that there is a red line on each side of the cen-
ter scale zero mark. This red line indicates 15 micro-

. ,

amperes on the 1500 microampere range. If the
pointer does not deflect beyond the red line after the
tube is heated, then the Microamperes switch can be
shifted to the 15 microampere position, and readings
taken on this low range. The instrument is in series

with the control grid patch cord jack at all times and,
therefore, will indicate grid current under all operat-

ing conditions.

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ELEMENTCURRENTMETER: A four range d-c milliam-
meter used to measure cathode, suppressor, screen,
or plate current. The Element Current Range switch
below the instrument serves to select either the 3, 12,

60 or 120 milliampere range. The Element Current
switch directly to the left of the range switch selects

the electrode in which the current is to be measured.

The Element Current meter has less than 75 milli-

volts drop in the electrode circuit to which it is con-

always has this meter on the correct range, and the
possibility of instrument overload is eliminated. The
particular range connected into the circuit is marked
for each group of potentials on the Heater Voltage

Selector switch plate. The voltmeter connections are

brought back through separate leads directly from the

tube socket thus providing a more accurate reading of
filament potential at the tube pins. Thus any voltage
drop in the leads from the filament transformer to

the tube socket will not be in the meter circuit.

nected. The switch is designed so that all other posi-

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tions are short circuited. This switch may be indexed
to any position at any time without effecting read-
ings.

CONTROLGRIDVOLTMETER:

Measurements of grid

bias potential are made on the Control Grid Voltage
meter. The switch to the right of the meter selects

either the 10, 50 or 100 volt range as required. Be
sure to note the position of this switch when unex-
pected plate current exists in the tube under check.

This switch also changes the bias network, de-
creasing the drop across the control grid potentio-
meter on the 10 volt range, providing better voltage
control when adjusting low bias potentials.

Note that the grid bias supply is regulated by an

OB2 regulator tube.

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FIG. 1

FIG. 2

ELEMENTVOLTMETER:

Electrode potentials are meas-

ured on the two range Element Voltage instrument
mounted below the Element Current meter. Plate,

screen, positive suppressor grid, or negative sup-
pressor grid potentials can be selected by using the

rotary switch below the meter (Refer to Fig. 3).

When selecting either Pos Supp or Neg Supp volts

position on the rotary Element Voltage switch, choose
the position indicated by the Supp-Pos-N eg toggle
switch located just to the left of the Model 686 name
plate. If the rotary switch is indexed to the wrong
position with respect to the positioning of the toggle
switch mentioned above, the Element Voltage meter
will read down scale. No damage will be done to
the voltmeter if a down scale reading should occur.

HEATERVOLTMETER:Filament potentials from 0.6 to

120 volts may be selected by means of a rotary
switch and potentiometer. These potentials are meas-
ured on a multirange a-c voltmeter (Refer to Fig. 2).

Note that the Heater Voltage Selector switch is
used to select the nominal voltage, and exact adjust-
ment is made by rotating the Heater Voltage Adjuster

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which controls the primary potential on the filament
transformer. An interlock circuit is used on the rotary
switch to automatically shift ranges on the filament
voltmeter as the switch is rotated. Thus the operator

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It must be remembered that when checking any
one tube, either a negative suppressor volts or a
positive suppressor volts (used for second anode
voltage purposes) can be selected, but not both for

the same tube test.

The Element Voltage Range switch directly to the
left of the meter selects the Element Voltage meter
range of 60, 150 or 300 volts. This switch is compen-
sated for meter loading so that the effect on validity

of readings is within 0.2%.

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