Dynascan B&K 667 Instrukcja obsługi - Strona 10
Przeglądaj online lub pobierz pdf Instrukcja obsługi dla Sprzęt testowy Dynascan B&K 667. Dynascan B&K 667 12 stron. Solid state tube tester
Drukuj stronęThe electrons flow from the grid to the plate then back through
the
power supply to the grid leak resistor Rg and up to the grid again.
Notice
that the voltage drop across the grid leak resistor Rg is such that it causes
the grid to go more positive than it normally would with no grid emission.
If a shght amount of "gas" is present in a tube, some of the electrons
from the cathode will collide with molecules of the gas and may knock off
one or more electrons, leaving positive ions
(ionization).
Some of these pos-
tive ions may then strike the grid, taking an electron from the grid to form
a gas molecule again.
The electron flow of this "gas current" is in the same
direction
as the "grid emission
current"
and
can
be
traced
on
Figure
4.
Notice again that the grid is made more positive by this "gas current'.
To achieve a sensitive grid emission or gas test, the circuit shown
in
Figure 5 is employed.
"|
==
SOLID
STATE
uae
D.C. AMP
METER
j
N
{11
+
FIGURE
5.
Grid
Emission
& Gas
Test
The
tube under test has its normal
plate voltage applied with the grid
biased beyond cutoff.
This
bias is applied to the tube under
test through
the 8.2 megohm resistor which is also the input resistor of the solid state
D.C. amplifier.
The
DC
amplifier is biased so that it is cutoff unless
the
tube is gaseous or its grid contaminated with some
of the cathode coating.
Then
current will flow from grid to plate of the tube through
the 8.2 meg-
ohm resistor.
This produces a voltage across the resistor which
is amplified
by the solid state D.C. Amp, causing a deflection of the meter.
The meter
is marked
"grid emission"
and
is divided
into two parts
for this test, the
reject area being above
10%
deflection and the good area below.
A meter
deflection of 10% is equivalent to a leakage of 100 megohms.
NOTE:
Some tube manufacturers recommend
that 10 Megohms
of grid
10