Heathkit SB-200 Arc path destruction list

SB-200 ARC PATH DESTRUCTION LIST

1. Metering Components (Most Vulnerable) Grid Current Meter Movement: The delicate coil and pointer mechanism are frequently destroyed or bent by the massive reverse current surge. Meter Shunt Resistors: The low-ohm resistors (e.g., 1.5Ω for grid current) connected across the meter can explode or open due to excessive current. Meter Protection Diodes: If installed (e.g., 1N4007 or 1N5408), these are sacrificial and will short or open to save the meter. They must be replaced after a severe arc. Plate Current Meter: Can be damaged if the arc current flows through the plate metering shunt (1Ω resistor). 

 2. Bias Supply Circuit Bias Rectifier Diode: The diode (e.g., 1N4007 series) in the bias supply can be blown open or shorted by the reverse voltage spike. Bias Resistors: High-value resistors (e.g., 47kΩ, 100kΩ) in the bias divider network can open or change value due to overload. Bias Capacitors: Electrolytic or film capacitors in the bias filter can rupture, leak, or short. Grid Resistors: The 33Ω grid stopper resistors (R21, R22) can open or burn if the arc current is sustained, though they often survive short events. 

 3. High Voltage (HV) Supply & Tank Circuit Plate Choke (RFC): The high-voltage RF choke can collapse (turns shorting together) or burn open due to the massive current surge from the filter capacitors. Plate Tuning Capacitor: The vanes can weld together, melt, or suffer carbon tracking on the insulation, rendering the capacitor unusable. Band Switch: Contacts can weld, pit, or melt; ceramic wafers can crack or suffer flashover damage. HV Filter Capacitors: While they are the source of the energy, they can internally short or vent if the arc creates a direct low-impedance path that exceeds their ripple/current ratings. HV Rectifier Diodes: The main power supply rectifiers can be shorted by the reverse surge if the arc reflects back into the supply. 

 4. Input & External Path Transceiver (Exciter): The most expensive casualty. RF and high voltage can travel back through the ALC line and input coax, destroying the radio's final transistors, ALC diodes, and input attenuators. Input Coupling Capacitors: Small value capacitors in the input network can puncture or short. Input Relay/Buffer: If a soft-key or relay buffer is present, its contacts or solid-state switches can weld or fail. Summary of Failure Modes Instant Destruction: Meter movements, transceiver finals, small signal diodes. Thermal Damage: Plate choke melting, capacitor vanes welding, switch contacts pitting. Overload Failure: Resistors opening, capacitors rupturing, fuses blowing. Note: The 10Ω surge limiting resistor and fuses added in the W8JI modification are designed to sacrifice themselves to prevent the destruction of the components listed above. If an arc occurs with these protections installed, check these two items first.