HP 400F, Operating And Service Manual, Page: 19 / 54

ModeI400F/FL
4-26. The meter, Ml. is a current driven device
that uti.l1zes a taut-band movement. It responds
to
the average value of the rectified meter amplifier
output. which is proportional to the rms value of the
sinusoidal signal being measured. The meter indicates
the rms value of the input voltage and
the power level
in dbm for resistive loads of 600 ohms. Measure­
ments across loads other than 600 ohms will be
indicated in db, but not dbm. The meter is protected
from
circuit overloads by diode CRI (400F) and
capacitor Cl (400FL).
4-27. POWER
SUPPLY.
4-28. The power supply provides both a positive
and negative 26 v regulated output. 1t may be operated
by external batteries (+35 v to 55 v and �35 v
to
55 v)
or line power (115 v or 230 v, 50 Hz
to
1000 Hz).
01795-1
Section IV
Paragraphs 4-26 to 4-30
4-29. The line input is converted to dc by a diode
rectifier network consisting of A2CR6 through A2CR9.
The positive output of the rectifier is applied to series
regulator A2Q4, which regulates the +26 v supply.
Control transistor A2Q6 has a constant emitter
reference voltage supplted by zener diode A2CR12.
CapaCitor A2C16 couples any change In the +26 v
output to the base of A2Q6, which wUl supply a signal
proportional to the change in output voltage
to
A2Q5.
A2Q5 will then amplify the signal and couple it
to
the base of
the regulator
A2Q4. causing it to regulate
the output by
either
increasing or decreasing con­
duction.
4-30. The -26 v supply is regulated in the same
manner, the only dUference being that the control
transistor A2Q7 is
referenced
to the +26 v output,
instead of the zener diode.
4-3