Power Cap Bleeder Guide

Filter capacitors can hold lethal voltage for minutes, hours, or — with a failed or missing bleeder — indefinitely after an amp is unplugged. A permanently wired bleeder resistor is the single cheapest, simplest thing you can add to a chassis to make every future power-down and every future tech who opens that chassis measurably safer.

What a Bleeder Actually Does

A bleeder is simply a resistor wired directly across a filter capacitor (or across the full B+ rail, spanning several caps in a multi-stage supply), permanently drawing a small, continuous current. That current slowly discharges the capacitor once the amp is powered off, instead of leaving the charge trapped with nowhere to go. Without one — or with a factory bleeder that's failed open, which happens more often than people expect — a filter cap can sit at full charge for days.

Bleeders serve a second, quieter purpose too: they give the supply a minimum load even with the amp on standby or with tubes pulled, which keeps voltage-doubler and choke-input supplies behaving predictably instead of ballooning toward unloaded peak voltage.

Sizing the Resistor

The tradeoff is straightforward: a lower resistance discharges faster but wastes more power continuously (and runs hotter); a higher resistance idles cooler but takes longer to bring the amp to a safe voltage. In practice, most guitar amp power supplies land comfortably with a bleeder discharging the caps to a safe voltage within 10–60 seconds, at a continuous dissipation most 1–3W resistors handle without complaint.

• Resistor type: metal film or metal oxide, flameproof, rated for continuous duty — this part runs warm all the time the amp is plugged in, not just during a fault.
• Wattage: calculate the continuous dissipation at your B+ voltage and chosen resistance, then rate the resistor at least 2× that figure for long-term reliability and headroom against line-voltage variation.
• Placement: mount it with clearance from other components and the chassis wall — it's a heat source by design, not an incidental one.

Wiring Diagram

Installation Steps

1. Discharge and verify first. Before installing a bleeder on an amp that doesn't already have one, treat every filter cap as live. Discharge with a proper discharge resistor on insulated leads and confirm 0V with a meter before touching anything.
2. Pick the tap point. On a single-stage supply, wire the bleeder directly across the main filter cap (B+ to ground). On a multi-stage supply with several RC-filtered nodes, a bleeder on the first, highest-voltage stage is the minimum; some builders add one at each stage for faster, more even discharge across the whole chain.
3. Mount it with clearance. Use a terminal strip, tag board, or standoff — never let the resistor body rest directly against the chassis, wiring insulation, or other components, since it runs continuously warm.
4. Solder and dress. Keep leads short and mechanically secure, routed away from AC mains wiring and sensitive grid circuits.
5. Verify it works. Power the amp up normally, run it briefly, then power down and time how long the B+ node actually takes to reach a safe voltage with a meter — don't just assume the math worked. Compare against the calculator above.