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====== Technical Profile: Pride "Amatuer" Dual-Tube Amplifier ======

===== 1. Unit Identification =====
  * **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.

{{ :kg7vfo:20251220_180432.jpg?nolink&600 |}}
===== 2. Internal Architecture =====
  * **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.

===== 3. Current Fault Analysis =====
The unit reportedly operates but is limited to **100 Watts** output. Potential "Cold Test" targets include:

^ Component ^ Symptom ^ Suspected Issue ^
| Parasitic Suppressors | Darkened/Cooked appearance | Resistor failed open; choking RF output path. |
| Input Swamp Bank | Resistor cluster near input | Drifting high or incorrect bypass "hack" limiting grid drive. |
| Mode/Tune Logic | Stuck in "Tune" or "AM-1" | Internal relay or rocker switch failing to engage high-bias state. |
| Tube Health | Visual debris in cooling fins | Tubes may have "gone soft" due to overheating. |
| Transformers | Surface rust on laminations | Potential insulation breakdown from moisture. |

===== 4. Testing Objectives (Cold State) =====
  * **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

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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
====== Technical Analysis: FM Mode Implementation ======

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.

===== 1. Technical Implications =====
  * **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.

===== 2. Market Identification =====
  * **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.

===== 3. Relation to 100-Watt Output Fault =====
  * **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.

===== 4. Diagnostic Notes (Cold Testing) =====
  * **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 vs. AM-2 Operational Differences =====
  * **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.