Heathkit TT-1 - Page 7

of a variable DC power
supply. C supply voltage is o
tained by using t¥6 AC sources (one fixed na
one tapped), two silicon rectifiers (CR-1 and
CR-2) and a charging capacitor (C-3). DC po-
tentials are applied to the voltage regulating
tube under test through a current limiting re-
sistor (R-7) which also serves as the regulating
resistor. A voltmeter circuit (R-5, R-6 and the
meter) indicates the firing voltage as the applied
potential is varied over the range in which the
tube should fire. The point at which the tube fires
is indicated by a sudden downward deflection of
the meter pointer. This occurs because it is the
property of a voltage regulator tube to main-
tain a voltage across its elements in the order
of five to thirty voits below its firing potential.
After the VR tube has fired, its value as a reg-
ulator can be determined by varying the applied
voltage between the limits specified on the roll
chart. Between these limits a variationfrom the
regulating point will be an indication of the tube's
THYRATRON TEST CIRCUIT
for their grid c
tinn eanahiliti
Veblen Ww Ap AN a se vd
nected into the
gram.
r
. The tube tob
est circuit, as s
x &
o}
2 B® 5
ct
De.
® ta
ok &
For this test the meter is connected inthe plate
circuit as a milliammeter. The tube is held to
cutoff by means ofa high bias applied to the grid.
When the bias is decreased so that the grid be-
comes less negative with respect to the cathode,
a point will be reached when the tube will sudden-
ly conduct and give an indication on the meter.
The value of BIAS setting at which this occurs
should fall within the limits specified in the
REMARKS column of the roll chart, For ex.
Ve ave See eS USS sl 25)
ample, a tube having "Thyra; Fire 15-0 Bias"
tha DEMADYS anlumn should fire hetwean
in LID ORVIUUVISARUEN UULUILIE OLIUUL £24E0U WUL WU
a BIAS setting of 15 and 0.
After the tube has fired, the pointer should fall
within the specified portion of the scale for the
tube to be considered good.
-_ . eS
HEATHKIT
—S
[RZ
67 2V. 2K 10W
fra (eri)
fires
at
110
en
let
us
assume
that
it
will
i
ating
potential
of
approximately
105
volts,
with
the
following
in
the
REMARKS
column:
"4.0
V
Reg,
Fil
5
to
70
V."'
Therefore,
when
the
FILAMENT
switch
is
rotated
from
5
to
70,
the
meter,
which
now
acts
as
a
voltmeter
across
the
VR
tube,
should
not
vary
more
than
4
volts.
If
the
variation
is
more,
the
VRtube
should
be
considered
faulty
and
replacement
is
recom-
mended.
ma ntain
fur] feat a1
eo ike OR iR3
620n oon
>——-5) | Be _|
|]
| |
oc
oc
BIAS PLATE
SUPPLY \ SUPPLY