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Technical Tips from Mark W. Persons |
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Harris 300 Watt Preamplifier Modification |
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September 28, 2013: This is a
Harris
992-7073-001 IPA module from a Harris HT-5 FM Transmitter. Its job
is to take 7 watts of exciter power and amplify it up to as much as 300
watts. Only about 100 watts is required to drive this transmitter
at the 4400 watt level. As you can see, four 2-watt carbon
composition resistors overheated and failed. I have seen this
before and the cure was to replace the resistors with larger ones and
the amplifier came back to life. Not this time. The
transistor failed too. That transistor is no longer available.
Harris has a replacement module for sale at about $3000. |
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| One answer to replace the transistor amplifier
card with a
Broadcast Concepts BLF278 300 watt pallet amplifier. The new
amplifier bolted down nicely on top of the original heat sink.
Some low-inductance resistors were added on the input side to reduce 7
watts of exciter RF power to about 3 watts. The amplifier is
designed to achieve 300 watts of output when the incoming power is 48
VDC. In this case, the power supply regulator in the transmitter
was set to 30 volts to achieve sufficient drive to the transmitter's
tube-type power amplifier. |
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The stories go on and on.
Stop in again sometime. I'll leave the soldering iron on for you.
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Questions? Email Mark Persons: teki@mwpersons.com |
