Complete Modern Parts List for All Heathkit SB-200 Modifications

Complete Modern Parts List for All Heathkit SB-200 Modifications The following is a comprehensive catalog of every known modification for the Heathkit SB-200, correlated with specific modern part numbers from Mouser and DigiKey. This list covers safety, performance, keying, and band-expansion upgrades. 1. High-Voltage Power Supply & Safety Modifications These modifications replace aging components to prevent catastrophic failure and improve reliability. Modification Component Spec Mouser Part # DigiKey Part # Purpose Capacitor Upgrade Filter Caps (x6) 330 µF / 450 V Snap-in 598-331A450M2PH 493-15716-ND Increases reserve capacity; reduces ripple. Bleeder Resistors (x6) 82 kΩ / 3 W Metal Oxide 283-82K-RC 82KQT-ND Replaces 30kΩ/10W; reduces heat by 95%. Soft-Start Inrush Thermistor CL-90 (10Ω, 5A) 527-CL90 2156-CL90-ND Limits transformer/capacitor inrush current. Bypass Relay (Kit) 120 VAC DPDT (Harbach SS-201) See Harbach Kit See Harbach Kit Bypasses thermistor after startup. Anode Protection "Glitch" Resistor 15 Ω / 10 W Wirewound 290-15-RC 15F10-ND Acts as secondary fuse during tube flashover. HV Fuse 2 A / 10 kV Ceramic 504-50200 F10200-ND Protects transformer from tube shorts. Damping Cap 4.7 nF / 3 kV Ceramic 80-C941U472KZS 399-11456-ND RF filtering on anode line. HV Metering Divider Resistors 1.5 MΩ / 1 kV Metal Film (x10) 299-1.5M-RC 1.5MQBK-ND Replaces open 4.7MΩ chain; safer voltage distribution. Meter Shunt Resistor 1.0 Ω / 5 W Precision 283-1.0-RC 1.0QT-ND Ensures accurate plate current reading. Harbach PM-200 SB-200 power supply kit View all 2. RF Deck & Stability Modifications Critical for preventing VHF parasitic oscillations that destroy tubes. Modification Component Spec Mouser Part # DigiKey Part # Purpose Parasitic Suppressors Plate Resistors (x2) 56 Ω / 2 W Carbon Comp 290-56-RC 56F2-ND Must be Carbon Comp; non-inductive. Suppressor Wire 14 AWG Teflon Stranded 566-1240-ND AE1014-ND 115mm length for hairpin loop. Grid Circuit Grid Caps (x2) 200 pF / 500 V Silver Mica 594-CD15FD201JO3 CD15FD201JO3-ND Low inductance grid grounding. Grid Resistors (x2) 33 Ω / 2 W Carbon Comp 290-33-RC 33F2-ND Matches grid load; prevents oscillation. Filament Choke RF Choke 25 µH / 3 A 546-190-253J15 M8660-ND Prevents RF on filament line. Bypass Cap 0.022 µF / 630 V Film 667-ECQ-U2223KL EF1126CT-ND Filters RF from filament supply. Plate Choke RF Choke 60 µH / 500 mA 436-1025-ND M4563-ND High voltage plate feed. Blocking Cap Doorknob Cap 500 pF / 7.5 kV 80-C941U501KZS 399-11455-ND Couples RF to tank; blocks HV. Heathkit SB-200 parasitic suppressor build View all 3. Modern Keying & Control Interface Allows safe connection to modern solid-state transceivers. Modification Component Spec Mouser Part # DigiKey Part # Purpose Soft-Key Interface Opto-Isolator 4N35 or TLP521-1 512-4N35 4N35-ND Isolates transceiver from HV. Switching Transistor 2N3904 NPN 512-2N3904BU 2N3904FS-ND Drives relay coil. Relay Driver Diode 1N4007 512-1N4007 1N4007FSCT-ND Protects transistor from relay kickback. Resistors (Assorted) 1kΩ, 10kΩ 1/4 W 299-1K-RC, 299-10K-RC 1KQBK-ND, 10KQBK-ND Biasing and current limiting. Meter Protection Protection Diodes (x2) 1N5408 (3A) or 1N4148 512-1N5408 1N5408FSCT-ND Clamps RF spikes across meter. Bypass Capacitor 0.01 µF / 50 V Ceramic 80-C315C103K5R 399-11114-ND Filters RF from meter movement. Lighting LED Lamp 6.3 V Warm White LED 512-LED63V (Generic) LED5MM-ND Replaces hot incandescent bulb. Dropping Resistor 1 kΩ / 1/4 W 299-1K-RC 1KQBK-ND Limits current to LED. Harbach SK-201 soft key schematic View all 4. Input Network & Band Expansion (160 Meters) Optimizes SWR and adds the 160-meter band. Modification Component Spec Mouser Part # DigiKey Part # Purpose Input Network Input Caps (80m) 560 pF / 1 kV Silver Mica 594-CD15FD561JO3 CD15FD561JO3-ND Optimized for modern solid-state drive. Input Caps (40m) 390 pF / 1 kV Silver Mica 594-CD15FD391JO3 CD15FD391JO3-ND Input Caps (20m) 220 pF / 1 kV Silver Mica 594-CD15FD221JO3 CD15FD221JO3-ND Reduces heating on 20m. Input Caps (15/10m) 56 pF / 1 kV Silver Mica 594-CD15FD560JO3 CD15FD560JO3-ND Compensates for stray capacitance. Trimmer Caps (Opt) 100 pF / 1 kV Ceramic 594-560-101J15 399-560-101J15-ND Allows fine-tuning of input SWR. 160 Meter Mod Toroidal Inductor 2.5 mH (Custom Wound) See Note See Note Series inductor for 160m tank resonance. Wire (Inductor) 18 AWG Enamel Magnet Wire 566-18AWG-RED MW18-ND Wind on T-106-2 or similar core. Relay (Switch) 120 VAC SPDT Heavy Duty 546-T92S11D12-120 PB118-ND Switches in 160m inductor. Connectors Input/Output Jacks SO-239 (UHF) Bulkhead 523-142-0201-202 ARF1055-ND Replaces proprietary connectors. Internal Coax RG-142 (Silver/Teflon) 566-1421-ND AE1021-ND High temp, low loss internal wiring. Heathkit SB-200 160 meter modification layout View all 5. Mechanical & Cooling Upgrades Improves thermal management and safety grounding. Modification Component Spec Mouser Part # DigiKey Part # Purpose Cooling Replacement Fan 4" (120mm) 115/230 VAC 527-109P0412 109P0412-ND Higher airflow (≥20 CFM) than stock blower. Fan Guard 120mm Metal Wire Guard 527-109-119 RMG120-ND Safety protection for fingers. Power Cord Grounded Cord 3-Wire 14 AWG with Plug 536-701960000 WK2030-ND Mandatory for chassis safety ground. Strain Relief Nylon Cord Grip 546-1501 HR1010-ND Secures power cord to chassis. Tube Sockets Ceramic Sockets 4-Pin Power (572B) 520-1423 AE1023-ND Replaces cracked/plastic originals. Hardware Ground Braid 1/2" x 0.032" Tinned Copper 510-1020-ND 1020-ND Heavy grounding for tuning caps. Implementation Notes 160 Meter Inductor: The specific inductance for the 160m mod depends on your tank coil. A common starting point is 2.5 mH wound on a T-106-2 iron powder core. You may need to experiment with turn count (typically 80–100 turns of #18 wire). Soft-Key Kits: While discrete components are listed, pre-assembled modules like the Harbach SK-201 or Ameritron ARB-704 are highly recommended for reliability and ease of installation. Carbon Composition Resistors: For parasitic suppressors and grid resistors, do not substitute metal film. The non-inductive property of carbon composition is essential for VHF stability. Wire: All internal RF wiring should be replaced with Teflon-insulated (RG-142/RG-316 type) wire to prevent melting near hot tubes.