• Manufacturer: Pride Electronics (California). Hy-Gain and Sonar Communications also used similar hardware
• Model: Likely a DX-3000 or a high-power variant of the KW-ONE.
• Production Era: Late 1970s.
• Defining Characteristics:
  • “AMATUER AMPLIFIER” typo on the brushed metal faceplate.
  • Red rocker switches for Power/Meter functions, riveted directly into the faceplate.
  • Rectangular chassis wider than the standard DX-300/KW-1 “cube” design.
  • Evidence of a missing adhesive-backed nameplate on the lower front panel.

• Vacuum Tubes: Two (2) 4CX250B (or similar) ceramic power tetrodes mounted in parallel.
• Cooling: Centrifugal squirrel-cage blower designed for a pressurized plenum.
• Power Supply: * Massive high-voltage plate transformer showing surface oxidation.
  • Separate filament/control transformer.
• RF Deck: * Large ceramic multi-tap tank coil for band switching (80M through 10M).
  • Dual variable capacitors for PLATE and ANT LOAD tuning.
  • Parasitic suppressors (resistor/inductor combos) connected to the tube anodes.

The unit reportedly operates but is limited to 100 Watts output. Potential “Cold Test” targets include:

• Objective 1: Use LCR meter to verify parasitic suppressor resistors (target ~47-100 Ohm).
• Objective 2: Check input attenuator resistors for value drift.
• Objective 3: Inject low-level RF via signal generator to trace signal loss through the band switch and grid drive circuit.
• Objective 4: Manually inspect blower rotation and clear debris from tube cooling fins.
• Objective 5: inspect and test passives under chassis.
• Objective 6: Perform out-of-circuit testing of each tube, filament characteristics, micro-mhos where possible

later on

• hot testing at lowered voltages with dummy load, measurement of all key power supply points and cathode, grid, suppressor and plate on the tubes as well as output and tuning.
• hot testing ramped up

out of scope (for now):

• resistor bypass switch
• 240V operation

The presence of a dedicated FM position on an HF amplifier of this era is highly unusual and provides specific insights into its design and origin.

• Efficiency and Bias: The FM setting likely switches the 4CX250B tubes from Class AB (linear for SSB) into Class C.
• Duty Cycle: Class C operation is non-linear but much more efficient, allowing the tubes to handle the 100% duty cycle (constant carrier) of FM without overheating.
• Voltage Regulation: In FM mode, the screen grid voltage and plate bias are adjusted to maximize saturation rather than linearity.

• Export Market Focus: While FM was rare for US hams on HF in the 1970s, it was popular in the European and South American “Export” markets for 10-meter and 11-meter operations.
• Pride Fingerprint: This specific mode sequence (AM-1, AM-2, SSB, CW, FM) is a definitive characteristic of late-production Pride Electronics units.
• Competitive Differentiation: Brands like Sonar and Hy-Gain (Afterburner) typically lacked a dedicated FM tap on their HF linear units.

• Switch Failure: If the Mode switch has carbon tracking or mechanical wear, the unit may be “latched” into a low-bias or TUNE state internally.
• Logic Conflict: If the bias relay does not engage the “High” voltage/current state when moving from FM to SSB, the output will hit a hard ceiling regardless of drive levels.

• Task: Verify continuity across the Mode switch wafers for each setting.
• Focus: Inspect the bias resistors connected to the FM/AM-1 positions for signs of thermal drift.

• AM-1 (Low Power): Designed for a “dead key” carrier of ~100W; used for tuning or low-drive AM.
• AM-2 (High Power): Enables full plate current for maximum RF swing; requires high airflow.
• Switching Logic: Changes the bias voltage on the 4CX250B grids and may switch plate voltage taps.