Daiwa LA-2035 issue?

Discussion in 'Amateur Radio Amplifiers' started by KJ7PJW, Aug 2, 2020.

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  1. KJ7PJW

    KJ7PJW Ham Member QRZ Page

    hello all new ham and new to this sight. i have a Daiwa LA-2035 that has a problem... radio with no amp in line SWR = 1.1 when i install the amp in line SWR = off the chart RED. i have the basic mutli meter but not sure how to diagnose what the issue is. any pointers would be grate.
     

    Attached Files:

  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    My first guess would be something wrong with the internal relay, RL2.

    If it's functioning properly, there's nothing in the amplifier that could create an extremely high input VSWR: The first thing the signal from the low-powered exciter sees is a purely resistive load, before the signal even hits the the amplifying transistor, Q1.

    However if Q1 is "blown out" to the extent it's a short circuit from base to emitter, that would effectively short-circuit the input and create very high VSWR looking into the amp.

    This is a super-simple, one-stage, one-transistor amplifier! All the "complexity" in the circuit relates to the receiving preamplifier and the carrier-operated switch which activates the relay, drives LEDs and stuff. If you could manually operate the relay RL2 and didn't care about the preamp, the whole amplifier could be one transistor and a tuned input and output circuit.

    Since these are only rated for 2-3W max drive power, "overdriving" it with excessive power is almost sure to blow the transistor Q1.

    Schematic:
    la-2035.PNG
     

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