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WHAT ARE THE DIODES D16 AND D18 IN THE SB-200 SCHEMATIC

  Based on the Heathkit SB-200 schematic and parts list, the diodes labeled D16 and D18 are 1N4007 (or originally specified as 1N2071 / 1N1319 in early manuals, which are equivalent general-purpose silicon rectifiers).  Function : These diodes are part of the ALC (Automatic Level Control) and metering protection circuitry. D18 specifically monitors plate current for the ALC system, developing a DC voltage proportional to the RF output to feed back to the transceiver. They are typically located near the meter switch and the 20nF (C12) and 2nF (often part of the meter calibration or bypass network) capacitors on the main chassis or meter board.  Specifications : Type : Silicon Rectifier PIV (Peak Inverse Voltage) : 1000V (for 1N4007) Current : 1A Replacement : A modern 1N4007 is the standard direct replacement. If your unit has been modified (as many SB-200s have), verify the orientation: the cathode band (stripe) usually faces toward the meter or the ALC output...
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572B Tube Operating Temperatures and Data

  572B Tube Operating Temperatures and Data The 572B tube is a high-mu power triode designed for RF and audio amplification, relying primarily on radiation and forced-air convection for cooling.  Key Thermal and Electrical Data: Maximum Envelope (Glass) Temperature: 250°C . Exceeding this limit risks softening the glass seal and causing vacuum failure. Plate Dissipation: Continuous (ICAS): 160 Watts per tube (some modern import versions are conservatively rated at 65–125 Watts due to thinner anode material). Peak (CCS): Higher short-term dissipation is possible, but modern tubes have reduced thermal mass compared to vintage US-made versions, limiting overload tolerance to seconds rather than minutes.  Cooling Method: Radiation and Forced Air .   The tube is not designed for conduction cooling through the base. Base Type: Ceramic (to withstand high temperatures), but the seal between the ceramic and glass envelope is the thermal weak point.  572B v...
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