SECTION IV
MAINTENANCE
4-1 COVER REMOVAL
Rack Model:
1. Toremove the dustcover, loosenandremovethefour screws
which fasten the cover to the back of the instrument, slide and
the cover toward the rear of the instrument.
2. To remove the bottom plate, turn the instrument on its back,
loosen and remove the four screws which fasten the plate to
the bottom of the instrument, and lift off the plate.
Metal Cabinet:
1. At the back of the instrument, remove the four screws which
fasten the rear cover to the chassis. Remove the rear cover.
2. Turn the instrument on its back. Remove the two large Allen
setscrews on the bottom, next to the control panel. Lift the
cabinet off the instrument.
4-2 TUBE REPLACEMENT
Any tube in the Model 206A may be replaced with a tube having
corresponding RETMA standard characteristics. All tubes are
accessible when the dust cover or cabinet is removed. Location
of tubes is shown in Fig. 3.
Whenever a tube in the oscillator, selective amplifier, or output
amplifier circuit is replaced, harmonic distortion in the output
' voltage sliould be measured with a distortion analyzer such as a
Hewlett-Packard Mode1 330B, 330C, or 330D. A replacement tube
having any serious departure from its average type characteris tics
can cause an increase in harmonic distortion the in output voltage.
Distortion should measure less than . 1% at frequencies above 50
cps, and less than. 25% at frequencies from 20 to 50 cps.
Replacement of any tube in the voltage regulator (tubes V11 to V14)
may cause a change in the level of the regulated voltage. Whenever
a tube in the regulator circuit is ~hanged~therefore, the level of |