Complete Amatron 811h Amplifier Power Supply Circuit Schematic Guide

The anode transformer for this RF linear stage demands a secondary winding rated at 1200VAC center-tapped, delivering 500mA under full load. Core selection should prioritize M6 grain-oriented silicon steel with a flux density of 1.4 Tesla to prevent saturation at 50Hz/60Hz operation. Primary taps at 115V, 200V, 230V enable universal mains compatibility–verify insulation between windings exceeds 2.5kV RMS for safety compliance with IEC 61010.

Rectification uses a full-wave center-tap configuration with UX-251 high-voltage diodes, each rated for 1500V reverse voltage and 1A forward current. Snubber networks (RC pairs: 10Ω 5W + 0.01µF 2kV MKT) across each diode suppress voltage transients during commutation, extending tube life by 30%. For ripple reduction, the first capacitor bank requires 40µF at 1.6kVDC–electrolytics arranged in series with balancing resistors (470kΩ 5W) to equalize leakage.

Voltage regulation employs a shunt regulator using a series pass vacuum tube (type GU-81M) in triode mode, configured for 600V plate-to-cathode with -80V grid bias. The bias network consists of a 250V zener stack (five 1N4764A in series) feeding a 10kΩ 10W wirewound potentiometer for fine adjustment. Overcurrent protection integrates a current-limiting resistor (1.5Ω 10W) in the cathode return path, tripping at 800mA to prevent damage to the output stage.

Grounding follows a star-point topology: the chassis ground connects to a single 12AWG copper bus, isolated from signal ground via 1MΩ 1W resistors. High-frequency decoupling capacitors (0.1µF 1kV ceramic) at each tube socket minimize RF feedback into the power rails. Mains filtering includes a common-mode choke (10mH @ 5A) followed by X2-class capacitors (0.22µF 275VAC) to meet EN 55032 Class B emissions.

High-Voltage DC Source Circuit for 811 Triode Tube Stages

Begin by implementing a dual-secondary transformer rated for 600–750V RMS per winding at 300–500mA. Connect secondaries in series for full-wave rectification using GZ34 or solid-state UF4007 diodes, ensuring reverse voltage margin exceeds 1.5kV. Filter capacitance should total 100–150μF (450V electrolytic pairs in series), with balancing resistors of 100kΩ/2W across each capacitor to equalize voltage stress and prevent leakage-induced failures.

Regulate the B+ rail with a VR150 gas tube or modern TL783 adjustable regulator, configured for 500–600V output. Incorporate a 10Ω/10W wirewound resistor in series with the input to limit current surges during tube warm-up. For bias supply, utilize a dedicated winding (90–120V RMS) rectified via 1N4007 diodes and smoothed by a 47μF/250V capacitor, feeding a 12.6V CT filament transformer in reverse to generate adjustable negative bias.

Ground return paths must converge at a single star point to minimize hum; avoid daisy-chaining chassis grounds. Test load regulation with a 10kΩ/50W resistor bank before connecting tube grids. Monitor ripple at 120Hz (full-wave) or 100Hz (Europe) using an oscilloscope–acceptable levels should not exceed 50mV P-P at full load.

Component Layout and Wiring for the High-Voltage Unit

Position the main transformer at the rear left of the chassis, ensuring clearance from the rectifier tube sockets and filter capacitors. Mount the HV choke adjacent to the transformer’s secondary winding output, minimizing lead length to reduce parasitic inductance. Use 18 AWG tinned copper wire for all high-current paths, securing branches with fiberglass sleeving rated for 5 kV dielectric strength.

Critical Wiring Routes

Connection	Wire Gauge	Routing Constraint
Rectifier plate to filter input	16 AWG	Keep >2 cm from control grid leads
Reservoir capacitor to choke	14 AWG	Avoid sharp bends; use 45° turns
Bleeder resistor to ground	20 AWG	Run along chassis edge, away from filament traces

Terminate all grounds at a single star point near the primary filter capacitor’s negative terminal. Route filament wiring in twisted pairs, maintaining 0.5-inch spacing from HV leads to prevent coupling. Secure bypass capacitors directly to tube sockets with the shortest leads possible–no longer than 6 mm–to suppress parasitic oscillations at startup.

Step-by-Step Soldering Guide for High-Voltage Sections

Use a temperature-controlled soldering station set to 350–400°C for high-voltage joints. Lead-free solder (e.g., Sn96.5Ag3Cu0.5) melts at higher temperatures, requiring precise heat application to avoid cold joints or component damage. For thick traces or chassis grounds, pre-tin both surfaces with a thin solder layer before joining–this ensures penetration into copper pours without excessive reheating.

Follow this sequence for high-voltage soldering:

• Component placement: Secure parts with Kapton tape or clamps; high-mass components (transformers, filter caps) exert mechanical stress during thermal cycling.
• Heat sink application: Clip a thin copper strip to PCB pads or leads acting as a thermal shunt to protect adjacent components from conductive heat.
• Flux management: Apply rosin-based flux (not water-soluble) sparingly–excess leaves corrosive residue that degrades insulation resistance over time.
• Joint formation: Hold the iron tip perpendicular to the pad, touching both the trace and lead simultaneously for 2–3 seconds to form a concave meniscus; avoid bulbous solder masses that create voltage stress points.
• Post-solder cleanup: Clean flux residue with isopropyl alcohol >90% and a stiff-bristle brush; inspect joints under 5x magnification for micro-fractures or insufficient wetting.

Critical Safety Measures

High-voltage sections demand ≥4mm creepage between adjacent conductors. Use fiberglass-reinforced PCB material (e.g., FR-4 with 1.6mm thickness) and coat exposed traces with silicone conformal coating post-assembly. Avoid soldering near electrolytic capacitors–their thermal sensitivity causes electrolyte evaporation, reducing lifespan. For force-cooled assemblies, ensure solder joints on thermal transfer paths (e.g., heatsinks, chassis mounts) have ≥10mm² cross-section to handle thermal cycling without cracking.

Critical Safety Measures When Assembling the High-Voltage Circuit

Discharge all stored energy in capacitors using a properly rated bleeder resistor before handling any components. A 1W, 10kΩ resistor across each high-value capacitor (470µF or larger) prevents residual charge build-up, reducing accidental shock risks exceeding 100mA–lethal even at low current levels.

Isolate the entire assembly during testing by placing it on an insulated workbench with a minimum dielectric strength of 25kV. Use only ESD-safe tools with insulated handles rated for 1000V to avoid short circuits, especially near toroidal transformers where flux leakage can induce unexpected arcing.

Ground all metallic chassis parts directly to a dedicated earth rod, not through shared outlets. Verify grounding continuity with a multimeter (

Install a properly sized fuse (fast-blow, 20% above nominal current) in series with the primary input. Replace fuses only with identical ratings–never jumpers–to prevent transformer saturation, which generates excessive heat and degrades core materials within seconds.

Use silicone-insulated wiring for all high-potential connections, avoiding PVC which degrades at temperatures above 80°C. Secure wires with nylon ties spaced at ≤10cm intervals to prevent abrasion against sharp edges or adjacent components vibrating at line frequency.

Place a 10MΩ resistor in parallel with any exposed high-voltage terminals to bleed off static charges. Even at 5kV, human skin capacitance (≈100pF) can store enough energy to damage sensitive semiconductors upon accidental contact.

Test for corona discharge in low-pressure environments using an ultraviolet detector. Even 5kV potential differences between closely spaced conductors (

Seal all high-voltage gaps with conformal coating (minimum 1mm thickness) to prevent dust buildup, which lowers effective air breakdown voltage from 3kV/mm to

Troubleshooting Common Issues in the Rectifier and Filter Stages

Check for blown fuses immediately if the output voltage reads zero or fluctuates erratically. Replace with an identical rating–never oversize. A 2A fuse substituted with a 5A variant risks catastrophic failure in downstream components, particularly smoothing capacitors rated at 450V DC. Use a DMM in continuity mode to verify the fuse’s integrity before proceeding.

Measure AC input at the bridge rectifier’s terminals. Expected values should align within ±5% of the transformer’s secondary winding specification (e.g., 320V AC for a 230V primary). Voltage drops exceeding 10% suggest degraded diodes or solder fractures. Swap suspect diodes with matched replacements–UF4007 for 1A applications, 1N5408 for 3A–ensuring correct polarity to avoid reverse current damage.

Capacitor Failure Signs

Bulging, leaking, or hissing capacitors demand immediate replacement. Test ESR with a dedicated meter; values above 3Ω indicate degradation. For circuits with 10,000μF reservoirs, replace with 105°C-rated components to extend longevity. Observe polarity strictly–reversed connections will rupture electrolytics within seconds under load. Parallel smaller capacitors (e.g., 220μF) to reduce ripple if primary storage fails transient response tests.

Excessive ripple on the DC rail–above 100mV peak-to-peak–often stems from dried-out capacitors or weak rectification. Use an oscilloscope to trace ripple frequency; 100Hz suggests full-wave rectification faults, while 50Hz points to half-wave leakage. Replace dual-diode modules as pairs to maintain balance. Clean corroded PCB traces with isopropyl alcohol and reflow solder joints to eliminate high-resistance paths.

Thermal runaway in the heatsink-mounted diodes signals insufficient cooling or overcurrent conditions. Verify thermal paste application and heatsink contact–gaps cause temperatures to exceed 90°C, degrading silicon. Install forced-air cooling if ambient temperatures exceed 40°C. For pulsed loads, add a snubber circuit (0.1μF + 10Ω in series) across diodes to suppress voltage spikes and extend component lifespan.