Initial Startup Guide (First Power-Up)

The “First Power-Up” protocol for fresh builds, rebuilds, and restorations.

Safely bringing up a newly built, extensively modified, or long-stored vintage tube amp for the first time is a disciplined ritual that prevents expensive component fireworks.

CRITICAL STEP: Always connect a proper speaker cabinet load or heavy-duty resistive dummy load before powering on any tube amplifier. Running a tube amp without a load can instantly flash-over output tube sockets, ruin output transformer windings, or destroy flyback insulation.

On the workbench Confirm the load and OT match before that first power-up — and if it's an amp with no bleeder, discharge it by hand first. Speaker Impedance & Cabinet Wiring Calculator Output Transformer Impedance Calculator DIY Dummy Load Box — no speaker on hand? build one DIY Cap Discharge Tool — bleed the caps by hand before you open the chassis

Comprehensive Pre-Power Checklist

Visual Audit: Inspect every single solder joint under bright light. Verify electrolytic capacitor polarities, diode orientations, and resistor values against the schematic layout line by line. (The Resistor Toolkit and Capacitor Toolkit make quick work of unmarked or faded parts.)
Cold Resistance Checks: With the amplifier unplugged and power switch on, measure resistance from the high-voltage B+ rails to chassis ground. Look for unexpected dead shorts or lingering bleeder resistor paths. Verify continuity of the safety ground wire from the IEC inlet to the chassis.
Incorporate the Current Limiter: Always plug your amplifier into a DIY Current Limiter (Dim Bulb Tester) for its maiden voyage to limit fault current safely if a major wiring error exists.

On the workbench No bleeder resistor path found on the cold-resistance check, or want to add one before first power-up? Power Cap Bleeder Guide — why it matters and how to install one Bleeder Resistor & Discharge Time Calculator

Step-by-Step Bring-Up Procedure

Naked Board Test: Power on the amplifier through the current limiter with no power tubes or rectifier tube installed initially. Keep preamp tubes in if you want to check heater paths. Flip the power switch on briefly. Watch the limiter bulb: a bright flash followed by dimming indicates normal capacitor charging. Confirm that filament/heater voltages read correct AC (approx. 6.3V or 5V) across tube socket pins.
Power Down & Populate: Unplug the unit, let the filter caps bleed down, and install your power tubes. Crank the bias adjustment trim pot to its absolute coldest setting—meaning maximum negative DC voltage on the control grids (Pin 5 on typical output tubes) to pinch off idle current entirely.
Mains power up via the current limiter. If the limiter bulb glows bright and stays bright, shut down immediately—you have a severe short circuit or wiring error. If the bulb glows bright initially and then dims down low, the power supply is stable. Proceed to check your B+ rail voltages and move directly to the Bias Adjustment Guide.

Don’t have a limiter box on the bench yet? Build the DIY Current Limiter first — you’ll need it for step one above.