Tektronix 502A, Instruction Manual

Page: 17 / 110

Operating Instructions—Type 502A
CUPS TO DEFLECTION PLATE PINS
NOTE:
TO AVOID GROUNDING
LEADS USE INSULATED
SLEEVING WHERE
NECESSARY.
4=0.1
nt
TO SIGNAL
SOURCE
tube sockets. Before connecting the resistors to the leads
from the amplifier, slip a piece of insulated sleeving (spa­
ghetti) over the wire. Then, after making the connections,
draw the sleeving back over the insulated resistor pigtail.
This will prevent the leads from accidentally shorting to the
chassis. The crt pins are easily bent and you must exercise
care when making these connections to avoid breaking the
glass seal.
CAUTION
Do not allow the leads from the oscilloscope am­
plifiers to touch the chassis when the power is on.
A short circuit of this type can damage the ampli­
fier circuits.
Fig. 2-13. Typical circuit for ac coupling to the crt deflection plates.
coupling is shown in Figure 2-13. Here, the leads from the
oscilloscope amplifier are removed and a resistor is con­
nected between each lead and
its respective crt pin. A
good value for this resistor in most cases is 1 megohm. The
vertical deflection plate pins are located on the sides of
the crt neck and the horizontal deflection plate pins are
located on the top of the neck.
A convenient method for connecting the resistors to
the crt pins is to use clips removed from standard miniature
If it is desired to couple the signal directly to the crt plates
(d c coupling), it will be necessary to supply positioning volt­
ages from the signal source. These voltages must also satisfy
the requirement of an average level of +225 volts,
mentioned previously. To dc couple the signal to the deflec­
tion plates, remove the leads from the crt pins and fold them
back, out of the way. Taping the ends of the wires will
prevent accidental shorting to the chassis. Connect the exter­
nal signal source to the pins of the crt.
The vertical deflection factor of the crt is approximately
13 volts per centimeter. The horizontal deflection factor is
approximately 17 volts per centimeter.
®1
2-11