I recently aquired a Palomar 225 linear amp (has black label & 2 MRF 455 pwr transistors, not blue label). It has a burnt (so badly I can't read the value) 2 or 3 watt resistor right next to the transmitter input. Does anyone know of a schematic for the amp? Or what other components maybe affected by the resistor burning? Thanks!
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Palomar 225 w/2 MRF 455's
- Thread starter fastfreddie1269
- Start date
That resistor is in series with the radio's drive power to the transistors. A pair of MRF455s only needs about ten or twelve watts peak to smack them fairly hard. Even a wimpy AM CB does half-again more or twice that. You'll be hard pressed to find a radio that small. The resistor serves two purposes. FIrst, to bleed off some of the radio's excess drive power, and to hold the amplifier's input impedance somewhere close to 50 ohms. The input of an amplifier should fool the radio into thinking that it's connected to an antenna with a low SWR. The resistor increases the amplifier's input impedance, hopefully to pin it near that 50-ohm mark. That resistor took it on the chin when somebody used a radio with two final transistors, or some other excessively-large output circuit.
That amplifier sure looks like the ones a friend was selling back around 96 or 97 when yours was probably made. The transistors are marked with a 1996 production date. The amplifier was probably built soon after that. I'll look to see if any diagrams of those amplifiers can be found next time I get to our shop.
73
That amplifier sure looks like the ones a friend was selling back around 96 or 97 when yours was probably made. The transistors are marked with a 1996 production date. The amplifier was probably built soon after that. I'll look to see if any diagrams of those amplifiers can be found next time I get to our shop.
73
