HP 400D Operating And Servicing Manual page 32

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NOTES:
1 . Heavy line indicates main circuit.
2. Light line indicates auxiliary circuits or controls.
are
3 . Variable catt r ols indicated by circle and dotted line dropped
10
from p:>1nt circuit where cormected. Line
screwdriver control.
4. Letters and numbers outside tube blocks indicate tube element
and
socket pin.
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DB
5, SI VOLTS (range) switch,
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circle indicates
Figure 4-3. Model 400D/H/L
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6. Conditions of voltage measurement
A. Input signal: . 3V rms,
B. DB VOLTS switch:
C . Between indicated point and ground.
will
7. Voltage vary with level of input Signal and p:>sition of SI;
should not exceed . 3V at
8. Signal measurements in first stage not practical due to ex­
tremely low signal level and large degeneration applied to V2.
-
9. CAUTION When checking tube V5, avoid Sborting crystal
diodes CRl and. CR2 to ground. With power turned on, the diodes
will if
out their terminals are shorted to ground.
burn
Servicing Block Diagram
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AMPLIfiER
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400
3V range
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