Preinstallation Procedures
15
MB-750D-H and MB-750D-H/40 Installation Manual
Bench Powering the MB-750S-H/40/E Amplifier
The recommended method of powering the amplifier on the bench is to apply ac from a 60 Vac
supply through a model SSP-PI power combiner to the input port. Alternate methods, such as
the use of a 24 Vdc power supply exist and can be used, but the method described here is
preferred. Sweep equipment must be calibrated with the power combiner in the signal leads to
avoid erroneous test results.
The sockets for the SX5B circuit breakers, or SX7F and SX10FA fuses should be vacant at this
point to avoid damage to test equipment by unintentionally applying 60 Vac. Special care should
be exercised to block power from test terminators which do not include a blocking capacitor.
Failure to do this will likely result in a damaged termination and the consequence may be a
misaligned amplifier.
Installing DF1-SS/40 Diplex Filters
Existing MB-750D-H amplifiers can be equipped with the new DF1-SS/40 diplex filters to extend
the bandpass of the return system to 40 MHz. The upgrade procedure is simple. To change
filters, remove the amplifier cover, unplug the existing 30 MHz diplex filters and replace with
the 40 MHz diplex filters.
The change in filters may degrade the impedance match on output ports 3 and 4, but there will
probably be no effect on picture quality.
To improve the impedance match at port 3, unwind the single turn coil, L13, and dress the wire
closer to the circuit board. Also, capacitor C41 should be bent slightly toward the connector.
Note that the lead wire from the capacitor is not insulated and must not touch the connector or
any other component. The components involved in this procedure are illustrated in Figure 8.
Figure 8
Restoring impedance match, port 3
