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Heathkit SB-200 power supply Rebuild notes ( for 8-10 Capacitors not suggested just notes)

 PLEASE BE AWARE THAT THIS POST IS SAVED NOTES AND NOT THE BIBLE OF WHAT TO USE OR DO. The original string used lower-rated diodes. For reliability with 220µF capacitors (and especially for Turbo mode), upgrade to 1000V+ 3A diodes. You need 10 diodes total (5 per leg of the doubler). Quantity: 10 Part Number: 1N5408 (1000V, 3A, Axial) Alternative: BY225 (1300V, 3A) for extra voltage headroom. Mouser: 512-BY225 or 625-1N5408 DigiKey: 1N5408E3/54GICT-ND 2. Bleeder / Equalizing Resistors Replace the original high-wattage wirewound resistors with modern 2W Metal Oxide or Carbon Film resistors. With 220µF caps, 82kΩ or 100kΩ provides perfect voltage balancing and safe discharge (~2 minutes) without excessive heat. Quantity: 8 (One across each capacitor) Resistance: 100 kΩ (Preferred for cooler operation) or 82 kΩ Power Rating: 2 Watt (Minimum), 3 Watt (Preferred for Turbo mode) Part Number: CFR-200JB-100K (2W, 5%) or MOX-200JB-100K (2W Metal Oxide) Mouser: 299-100K-RC (Ohmite 2W) DigiKe...
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Diagnosing a bad Harbach soft key modification in a Heathkit SB-200 amplifier

  Diagnosing a bad Harbach soft key modification in a Heathkit SB-200  am plifier involves verifying whether the modification is present, checking for correct wiring, and testing the keying behavior with and without the mod engaged.  The Harbach soft key was designed to protect modern solid-state transceivers from the SB-200’s high negative keying voltage (approximately –120 VDC) by interposing a relay or FET. A faulty installation or failed components can cause keying issues such as the amp staying keyed, not keying at all, or damaging the transceiver.  Step-by-step instructions Tools and Materials Multimeter (capable of measuring DC voltage and continuity) Dummy load (for safe testing) Shorting plug or mechanical switch for keying jack SB-200 schematic (preferably with Harbach mod annotations) Insulated tools and safety equipment (high voltage is present)  Prerequisites Ensure the amplifier is unplugged and discharged before opening the chassis. Confirm whethe...
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SB-200 Plate Meter Design with GC9A01 & Arduino Nano

 SB-200 Plate Meter Design with GC9A01 & Arduino Nano This design replaces the analog meter in your Heathkit SB-200 with a digital gauge on a 1.28" GC9A01 Round TFT. It measures plate current via a shunt resistor and displays it on a colorful, animated dial. 1. Hardware Connections Critical Warning: The GC9A01 is a 3.3V logic device.  The Arduino Nano is 5V. You must use a logic level converter or series resistors (220Ω–330Ω) on the SPI lines (MOSI, SCK, CS, DC) to prevent damage.  GC9A01 Pin Arduino Nano Pin Note VCC 3.3V Do NOT use 5V GND GND Common Ground CS D10 Chip Select DC D9 Data/Command SDA (MOSI) D11 Data In (Use 220Ω resistor) SCL (SCK) D13 Clock (Use 220Ω resistor) RST D8 Reset (Optional, can tie to 3.3V if not used in code) BL 3.3V Backlight (Or PWM pin for dimming) Current Sensing Circuit (Shunt): The SB-200 cathode current (Plate + Grid) flows to ground. Insert a low-value shunt resistor in the cathode ground path. Sh...
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This design utilizes the Hosyond 3.5" ESP32 (ST7796U) to replace the SB-200's mechanical meter with a digital multi-function display. It measures High Voltage (0–3000V), Plate Current (0–600mA), and Grid Current (0–150mA) using isolated sensing circuits safe for the ESP32's 3.3V ADC.

 This design utilizes the Hosyond 3.5" ESP32 (ST7796U) to replace the SB-200's mechanical meter with a digital multi-function display.  It measures High Voltage (0–3000V), Plate Current (0–600mA), and Grid Current (0–150mA) using isolated sensing circuits safe for the ESP32's 3.3V ADC.  ⚠️ Critical Safety Warning Lethal Voltage: The SB-200 contains 2,400V+.  The voltage divider must use high-voltage rated resistors (series string) to prevent arcing and resistor failure.  Isolation: The ESP32 ground MUST be connected to the SB-200 chassis ground (Common Ground) for these resistive dividers to work.  If you cannot ensure a solid common ground, use Hall Effect sensors (e.g., ACS712/ACS758) or opto-isolators instead of direct resistive dividers. RF Protection: All input lines to the ESP32 must have RF bypass capacitors and clamping diodes to prevent RF feedback from damaging the microcontroller.  1. Hardware Interface Design The Hosyond module uses the ST7...
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The Definitive Guide to the Heathkit SB-200 Linear Amplifier (Incomplete)

 The Definitive Guide to the Heathkit SB-200 Linear Amplifier ////////////Table of Contents////////////// Introduction & Historical Context Technical Architecture & Circuit Theory Complete Parts Inventory & Modern Equivalents Restoration & Safety Protocols Performance Modifications (The "Turbo" & Stability) Band Expansion (160 Meters & WARC) Advanced Projects: Automated Bias Control Troubleshooting & Maintenance Legacy & Collector’s Market  Chapter 1: Introduction & Historical Context 1.1 The Birth of an Icon The Heathkit SB-200 was introduced in August 1964 as part of Heathkit’s revolutionary "SB" series, designed to compete with the Collins KWM series.  Priced at $200 (kit form), it was engineered by John Schlagenhauf to be the affordable companion to the SB-400 transmitter. 1.2 Production Timeline SB-200 (1964–1978): The original model covered 80, 40, 20, 15, and 10 meters.  It remained virtually unchanged for 14 years, a testa...
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