Rectifier Versions
Author: Kevin M Date Posted:15 April 2026
Rectifier Tube & Solid-State Guide
5AR4/GZ34, 6CA4/EZ81, 5U4GB, 5Y3 & Solid-State Plug-in Replacements — Understanding voltage drop, sag, and replacement options available at Evatco.
Popular Tube Rectifiers At A Glance
5AR4 / GZ34
"Direct Equivalent Pair: High Voltage, Minimal Sag"
5AR4 (US RETMA code) and GZ34 (European code) are identical, interchangeable tubes. Known for high current capability, indirect heating (slow turn-on), and low voltage drop.
6CA4 / EZ81
"Direct Equivalent Pair: Compact Powerhouses"
6CA4 (US code) and EZ81 (European code) are completely identical 9-pin rectifiers used in smaller vintage amps (like Vox AC15, Watkins Domino, and Marshall 18W clones).
5U4GB / 5U4G
"The Heavy-Sag Workhorse"
Directly heated rectifier with higher internal resistance. Delivers moderate voltage drop and noticeable touch-sensitive "sag" when pushed hard. Classic in Fender Tweeds and Mesa Boogies.
5Y3GT / 5Y3
"Maximum Vintage Sag & Compression"
A classic low-current octal rectifier used in vintage low-wattage amps (like the Fender Champ or Deluxe). High internal resistance causes high voltage drop and legendary vintage compression.
Solid-State Plug-Ins (Yellow Jacket / Copper Cap)
"Zero Sag, Maximum Punch & Extended Life"
Solid-state diode plug-ins replace vacuum rectifiers in standard octal sockets. They remove heater current draw from the transformer, raise B+ voltage slightly, and eliminate power sag for ultra-tight bass response.
Rectifier Voltage Drop & Socket Comparison
| Model / Variant | Socket Type | Filament Draw | Voltage Drop (Sag Level) | Replaced By Solid State? |
|---|---|---|---|---|
| 5AR4 / GZ34 | Octal (8-Pin) | 5V @ 1.9A | Low (~10V - 15V drop) | Yes (Increases voltage slightly, eliminates sag) |
| 6CA4 / EZ81 | Noval (9-Pin) | 6.3V @ 1.0A | Low to Medium (~15V - 20V drop) | Yes (Via 9-pin solid-state adapters) |
| 5U4GB / 5U4G | Octal (8-Pin) | 5V @ 3.0A | High (~40V - 50V drop) | Yes (Substantially increases B+ plate voltage) |
| 5Y3GT | Octal (8-Pin) | 5V @ 2.0A | Very High (~60V drop) | Yes (Warning: Increases B+ voltage significantly) |
| Solid State Plug-In | Octal (8-Pin) | 0A (No filament draw) | Near Zero (~1V - 3V drop) | Direct solid-state conversion plug |
Popular Models & Replacements at Evatco
JJ Electronics 5AR4 / GZ34
A reliable high-voltage octal rectifier. Perfect standard replacement for Vox AC30, Fender GZ34 circuits, and Hi-Fi amplifiers.
Electro-Harmonix 5U4GB
Sturdy, heavy-duty build designed for high demand. Excellent natural compression and warm dynamic response under load.
JJ Electronics EZ81 / 6CA4
Compact 9-pin miniature rectifier. Provides smooth, consistent power for classic 18W and 15W push-pull circuits.
Solid-State Plug-In Modules
Replaces 5AR4, 5U4, and 5Y3 octal rectifiers. Reduces power transformer heat, tightens bass, and boosts clean headroom.
Important Technical & Safety Disclaimer
Please Note: This information is provided as a basic overview and should be used as a general guide only. Rectifier substitution directly impacts the high-voltage DC (B+ supply) in your amplifier. Replacing a high-sag tube (like a 5Y3 or 5U4) with a low-sag tube (5AR4/GZ34) or a solid-state rectifier plug-in (like a Yellow Jacket or Copper Cap) will significantly increase the internal operating voltages, potentially exceeding the voltage ratings of power supply filter capacitors or bias limits. Always verify your transformer rating, filter capacitor voltage limits, and re-bias your amplifier when swapping rectifier types.
