1. History & Specifications

The Heathkit SB-200 was introduced in 1964 at a kit price of US$200 and remained in continuous production until 1978 — a longer production run than any other Heath SB-Line product.¹ It was designed as the companion amplifier to the SB-Line transceiver family and operates on all five amateur HF bands from 80 to 10 metres.

In 1978, US FCC regulations prohibited the manufacture of amplifiers capable of operation on the 10-metre band. Heath responded with the SB-201, an electrically identical unit with the 10-metre band removed from the band switch and tank circuit. The SB-201 was produced through 1983. All restoration procedures in this guide apply equally to both models unless noted. Conversion of an SB-201 to SB-200 specification by adding the original 10-metre tank components is straightforward and well-documented in the community.²

The SB-200 is notably more compact than the SB-220, which followed it in the Heathkit lineup. Its lower HV rail (~2,400 V vs. ~3,000 V) and the less demanding 572B tube make it somewhat more forgiving to restore, but the same fundamental high-voltage hazards apply and must be treated with equal respect.

2. Pre-Restoration Assessment

2.1 Initial Cold Inspection

Before ordering any parts or energising the amplifier, perform a thorough cold visual inspection with the AC cord unplugged:

• Examine the 572B tube envelopes for cracks, white or milky getter deposits (indicating lost vacuum), or heat-deformed base pins. A healthy 572B has a bright silver getter flash.
• Inspect the HV power supply board for bulging or leaking electrolytic capacitors, burnt PCB laminate, and discoloured or open resistors. Carbon composition resistors throughout the SB-200 drift significantly with age — values 20% or more out of spec are common on unrestored units.³
• Check the plate transformer for evidence of overheating — darkened varnish, burnt smell, or discoloured primary and secondary leads.
• Inspect the plate HV choke (RFC) for burnt enamel or broken winding. This is a documented failure point, especially on units run at high duty cycle.
• Examine the band switch wafers for arcing pits and carbon tracking. Arcing damage here usually indicates prior parasitic oscillation problems.
• Check the RCA phono RF input connectors (a known weakness — see Section 3.2).
• Verify the top-cover interlock switch actuates correctly and that the interlock wiring is intact.

2.2 Required Test Equipment

• High-voltage digital multimeter — minimum 4,000 V DC range (Fluke 117 or equivalent)
• RF wattmeter, 1.5–30 MHz, 1,000 W range minimum (Bird 43 or equivalent)
• 50Ω dummy load rated 1,000 W or better
• Resistance meter capable of measuring both low-value (0.1Ω) and high-value (>10MΩ) resistors
• Variable bench power supply for initial low-voltage relay and fan checks

3. Internal Circuits — Component Restoration

3.1 Power Supply Section

The SB-200 uses a conventional full-wave bridge rectifier (not a voltage doubler as in the SB-220) fed from the plate transformer secondary. The resulting ~2,200–2,400 V DC is filtered by a bank of series-connected electrolytic capacitors on the dedicated HV board. Bleeder/equaliser resistors across each capacitor provide voltage balance and a discharge path when power is removed.

The Harbach PM-200 is a complete drop-in replacement for the original HV board. It uses modern 330µF / 450 V capacitors, 1,000 PIV 3 A diodes, 82kΩ / 3 W bleeder resistors, and a precision high-voltage meter divider string. For any SB-200 of unknown service history, installing the PM-200 is strongly recommended over attempting to reform and re-use original components.⁴

3.2 RF Deck — Tank Circuit & Input Network

The SB-200 uses a switched pi-network output tank with a roller inductor and variable plate and load capacitors. Per-band input pi-networks optimise the 50Ω drive impedance for each band. The 572B triode is inherently more susceptible to VHF parasitic oscillations than the 3-500Z, particularly on 10 metres — making parasitic suppressor condition a high priority in any restoration.⁵

3.3 Metering, Relay & Keying Circuits

The SB-200 provides plate current and plate voltage metering. The original keying circuit is designed for the SB-Line transceiver family and uses relay activation via the transceiver’s transmit keying line. Like the SB-220, this circuit is incompatible with modern low-level PTT outputs without modification.

4. Safety: High Voltage, Bleeder Resistors & Interlocks

4.1 Bleeder Resistors — Function and Failure

The bleeder resistors across each section of the filter capacitor bank serve two functions: they equalise voltage across series-connected capacitors during operation, and they provide a discharge path for stored charge after power is removed. Without functioning bleeders, the filter capacitors will retain their full charge indefinitely after the AC mains are disconnected — this stored charge is lethal.⁶

Critically, a failed bleeder resistor leaves no visible external indication. An open-circuit bleeder causes the affected capacitor to retain full charge without any mechanical or visual symptom. This is why voltmeter verification before internal access is non-negotiable — relying on time elapsed since power-off is not safe practice.

An additional physical phenomenon makes bleeder verification even more important: large electrolytic capacitors exhibit dielectric absorption. Even after an apparently complete discharge, energy stored in the dielectric layer can recover to the capacitor terminals over a period of seconds to minutes. This means a capacitor that tested near zero volts immediately after discharge can rise to several hundred volts minutes later if the bleeder is not permanently connected.⁷

4.2 The HV Interlock

The SB-200 incorporates a top-cover interlock that disconnects or grounds the HV circuit when the cover is removed. While this provides a degree of protection during casual operation, it must not be relied upon as the primary safeguard during restoration work, for two reasons:

• The interlock switch contacts can become corroded or fail to make reliable contact after decades of inactivity.
• If the interlock abruptly shorts HV to ground while significant charge remains on the capacitor bank, the discharge current can destroy the meter shunt resistors and potentially damage the meter movement, as documented in SB-220 restoration literature for the same circuit topology.⁸

The correct procedure is to wait for the HV to bleed down via the bleeder resistors, confirm zero voltage with a meter, and only then remove the cover. The interlock provides a secondary layer of protection; it does not replace deliberate, verified discharge.

4.3 Safe Discharge Procedure

  STEP 1 ─── Switch amplifier to STANDBY, then set AC power switch to OFF
                │
  STEP 2 ─── Unplug the AC mains cord from the wall outlet
                │
  STEP 3 ─── Wait 5 minutes minimum
             (82kΩ bleeders in PM-200 discharge 330μF caps in ~4RC ≈ 4 min)
                │
  STEP 4 ─── Set multimeter to 4000V DC range.
             Probe (+) to HV positive terminal on filter cap bank.
             Probe (-) to chassis ground. Confirm reading < 50V.
                │
  STEP 5 ─── (Optional but recommended) Discharge stick:
             10kΩ / 25W resistor on insulated probe, clip lead to chassis.
             Touch probe to each capacitor positive terminal for 10 seconds.
                │
  STEP 6 ─── Re-measure. Confirm < 10V on all HV nodes.
                │
  STEP 7 ─── Now safe to open cover and work internally.
             ──────────────────────────────────────────────────
             NOTE: Dielectric absorption can cause charge to
             recover after discharge. Re-verify before each
             work session even if only briefly away from bench.

Figure 1. SB-200 safe high-voltage discharge procedure before internal access.

4.4 AC Line Safety Capacitors

Small ceramic bypass capacitors across the AC mains are used in the SB-200 for RFI suppression. Any capacitor connected directly across the AC line or from line to chassis must be a certified Class X2 (line-to-line) or Class Y2 (line-to-chassis) safety-rated component. Standard ceramic disc capacitors are not rated for mains use; if one fails short, it puts mains voltage on the RF chassis, creating a lethal shock and fire hazard.

Inspect every capacitor in the mains input section. If any standard ceramic disc (non-line-rated) capacitors are found across the AC line or from line to chassis, replace them immediately with correct Class X2 / Y2 types. Harbach Electronics stocks the correct line-rated ceramic bypass capacitors for the SB-200/201.⁹

4.5 ALC Output Warning

The SB-200 produces an ALC (Automatic Level Control) output voltage that can reach very high negative values — well beyond the −9 V maximum that many modern Kenwood and other transceivers accept before shutting down transmission. Connecting the SB-200 ALC output directly to a modern transceiver without a clamping circuit risks damaging the transceiver’s ALC input. Either build a zener-diode clamp at approximately −9 V, or do not connect the ALC line at all, managing drive power manually.¹⁰

5. Cabinet Restoration

5.1 Paint

The SB-200 uses the same Heathkit SB-Series grey-green cabinet finish as the SB-220 and other SB-Line equipment. As with the SB-220, Heath used multiple shades of this colour across production, and precise colour matching to a specific unit is not reliably achievable. A full recoat is the correct approach for any cabinet with significant paint degradation; spot touch-up on an aged cabinet will always be visible due to the natural fading of the original finish.

• MyPerfectColor — myperfectcolor.com — acrylic enamel spray and brush paints computer-matched to original Heathkit SB-Series metal swatches.
• Sherwin-Williams formula (K9STH) — k9sth.com — the definitive computer-matched formula for the preferred SB-Line light grey-green; any paint store can mix from this formula.
• N5OLA Restoration Supplies — willeverett.net/n5ola.html — SB-Line matched paint in 11 oz spray can or 1 oz touch-up bottle.

5.2 Cabinet Preparation & Painting

• Remove all knobs, hardware, rubber feet, and any panel overlays before stripping.
• Degrease thoroughly with acetone or MEK; sand with 220-grit to provide adhesion.
• Apply a self-etching primer on bare steel before applying the colour coat.
• Apply two light coats of colour-matched acrylic enamel with full cure between coats.
• The SB-200 top panel includes the two circuit breaker buttons — these must be masked or removed before painting.

5.3 Front Panel Overlays

The SB-200 / SB-201 front panel uses silk-screened lettering over a green-anodised aluminium panel. Replacement vinyl overlay kits faithfully reproducing the original artwork are available on eBay from restorer community sellers. These adhere over the existing panel and provide a professional result without requiring re-silkscreening.

5.4 Hardware, Knobs & Cables

6. Recommended Modern Upgrades Summary

7. Parts Sources & Reference Documents

• Harbach Electronics (KB1SEL) — harbachelectronics.com — the primary dedicated SB-200/201 restoration parts supplier. Stocks the PM-200 HV board, SK-201 soft-key, SS-201 soft-start, AG6K parasitic suppressors, Ohmite grid resistors, silver mica grid caps, meter diodes, SO-239 connectors, 431-13 terminal strip, SWI-100 band switch wafers, meter lamp, HV cable, and the SB200/201 Master Kit ($548).
• RF Parts Company — rfparts.com — 572B replacement tubes, cabinet feet, SO-239 connectors.
• W6ZE / OCARC Heathkit of the Month #33 (R. Eckweiler) — w6ze.org — excellent circuit description and operational overview of the SB-200.
• WA3DSP SB-200 Restoration and Modifications — crompton.com/hamradio/heath/sb200 — detailed photographic restoration log including Harbach board installation, Teflon rewiring, filament choke upgrade, and transformer rewiring. A comprehensive practical reference.
• Wireless-Girl.com SB-200 Mods — wireless-girl.com — comprehensive guide covering Harbach soft-start installation, arc protection, RCA connector replacement, parasitic suppressors, and tube conditioning.
• AE1S SB-200 Restoration Blog (Parts 1 & 2) — blog.kotarak.net — detailed engineering rebuild with photographic documentation; covers Harbach board installation, AG6K parasitic suppressors, ceramic tube sockets, band switch cleaning, and component replacement rationale.
• MyPerfectColor SB-Series Cabinet Paint — myperfectcolor.com — custom acrylic enamel matched to original Heathkit SB-Series cabinet colour.