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--- kg7vfo:start [2025/12/28 17:58] – [4. Testing Objectives (Cold State)] admin
+++ kg7vfo:start [2026/01/13 15:52] (current) – external edit 127.0.0.1
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 ===== 1. Unit Identification =====
-  * **Manufacturer:** Pride Electronics (California).
+  * **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.
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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.