Heathkit HD-1250 - To Find an Unknown Capacitor Value

Page
50
TO FIND
AN
UNKNOWN
CAPACITOR
VALUE
Refer to Figure 3-3
for the following
steps.
1
.
Connect
the unknown capacitance
across
a
phono
socket as shown.
2. Plug any of
the pickup coils, except
the brown
coil, from the
dip meter
set
into the phono
socket.
3.
Adjust
the Dip Meter for use
in the
injection
mode of operation.
NOTE:
By trial and error, you may
need to plug any of the remaining
coils into
the
coil socket on the Dip Meter
to determine the resonant
frequency of
the "test circuit." Record
the frequency {f
),
in
MHz,
from
the dial.
4.
Refer
to Table A and find the
color
of
the coil which you used in
the
phono
socket. Record the value of
the
inductor
(L) in henries.
5.
Substitute
the recorded quantities
in the formula below
to determine the
value of the unknown
capacitor in
farads:
47r
2
f
2
L 39.48 xf
2
xL
Note:
1 MHz
=
10
6
Hertz
1
nF
=
10"
6
farads
1 pF
=
10-'
2
farads
f
=
dial reading (MHz)
L
=
Inductance (in
Henries)
COIL
COLOR INDUCTANCE