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How to Remove the SWR Bridge from Your Heathkit SB-200

  How to Remove the SWR Bridge from Your Heathkit SB-200 The internal SWR bridge in the Heathkit SB-200 is a convenient feature, but it can introduce insertion loss, become a point of failure, or limit peak power handling. Removing it creates a direct, low-loss path from the Pi-network to your antenna.  This guide covers the removal process with ASCII schematics, formatted for easy reading on your blog. ⚠️ High Voltage Warning: The SB-200 contains lethal voltages. Always unplug the unit, wait at least 5 minutes for capacitors to discharge, and short the high-voltage capacitor terminals to the chassis with an insulated screwdriver before touching any internal components.  1. Understanding the Stock Configuration In the stock SB-200, the RF path flows from the Pi-network output capacitors, through the directional coupler (SWR bridge), and finally to the rear SO-239 antenna connector.  Stock RF Path: [ Pi-Network Output ] -----> [ SWR Bridge ] -----> [ Antenna...
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How-To: VHF Stability & Grid Protection for the Heathkit SB-200

Stabilizing the Heathkit SB-200: A Guide to VHF Parasitic Suppression & Grid Protection The Heathkit SB-200 is a legendary amplifier, but like many vintage designs, it can suffer from VHF instability (parasitics) when using modern 572B tubes or operating on the 10-meter band.  The following guide adapts proven engineering techniques—specifically cathode input swamping and grid fuse protection —to ensure your amplifier remains stable and your tubes stay safe.  ⚠️ Safety Warning: This project involves high voltage and internal amplifier modifications. Always disconnect power, wait for capacitors to discharge, and short the high-voltage points to ground before touching internal components.   If you are unsure, consult a qualified technician. 1. The Theory: Why Modify? Modern 572B tubes can exhibit different internal capacitance characteristics than the originals. At Very High Frequencies (VHF), energy can feed back from the plate to the cathode through the tube...
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