Broadcast Technical Consulting and Sales
10032 Island Drive, Brainerd, MN
Tips from Mark W. Persons
Harris 150 Watt Preamplifier
This is a
992-6842-001 150 Watt Preamplifier, which is used in the Harris FM25K1,
FM20/25K2, HT20/25, FM30/35K, and HT30/35FM transmitter designs for 88
to 108 MHz. I think that "preamplifier" is a bad choice of names.
In my opinion, it should be called the 1st IPA (Intermediate Power
Amplifier). The rear circuit card is a power supply voltage regulator.
Transistors on the front RF module are no longer made. Harris wants $3200 for a replacement
unit. It is of a more recent design which includes the power supply
regulator and heat sink.
An alternative is to
Broadcast Concepts BLF278 RF Pallet Amplifier, sometimes referred to
as the FM300 FM Broadcast Amplifier. This more
recent amplifier design is about $250 and is physically smaller even though it
is capable of producing 300 watts of RF output with 48 VDC power.
In this case, the Harris voltage regulator keeps the supply to just 32
volts maximum. This is just right for 150 watts output.
The new pallet amplifier has more gain
so a 6 dB RF pad at its input is required to reduce 8 watts of RF to 2
watts, which is what the amplifier wants to see.
The BNC input
and output jacks were removed and mounted to the Harris heat sink to
accommodate the new module.
This modification worked quite well
for one of our clients.
Work in our shop is done on a time and
material basis. A modification of this sort runs about $550.
The stories go on and on.
Stop in again sometime. I'll leave the soldering iron on for you.
Mark W. Persons
page last edited