octal base (Uf=5 Volt) two way rectifier tube types: GZ34, CV1377, 5AR4, GZ34s

GZ34 / 5AR4 rectifier tube – selection, interchangeability, and use as a full-wave rectifier in tube power supplies

What is a GZ34 (5AR4) and what is it used for?

The GZ34 is a full-wave rectifier tube (double-way rectifier) that converts AC to DC in the power supply of tube amplifiers and tube equipment. It is used in guitar amplifiers, hi-fi amplifiers, preamplifiers, and some radio sets when a tube-typical start-up behavior and a comparatively “soft” B+ supply in terms of dynamics are desired.

Unlike some directly heated rectifiers, the GZ34 is an indirectly heated type, which often supports a slightly delayed rise of the DC voltage. In practice, the rectifier defines the power-supply behavior: voltage drop under load, inrush current, current reserve, and therefore the operating conditions of the following stages—audible in some guitar amps as dynamics, compression, or “sag.” When using these tubes, it is important to consider not only voltages and currents but also the size of the first input capacitor (reservoir capacitor), because peak currents can become critical.

Which names belong to the family: 5AR4, CV1377 and GZ34s?

The GZ34 family includes the designation 5AR4 (international/US name) as well as the now very rare military version CV1377. GZ34s commonly refers to the JJ version built to the same concept, using a spiral heater structure intended to reduce hum coupling.

For end customers it is important to identify the correct family so that base, heater requirements, and load capability match the amplifier. For workshops, service operations, and OEM use, documenting the exact version used is useful, because real-world voltage drop and reserve can vary slightly by production batch and internal construction.

Are GZ34, 5AR4, CV1377 and GZ34s interchangeable, and where are the exceptions?

GZ34, GZ34s, 5AR4 and CV1377 are functionally equivalent in many devices and are often used interchangeably, provided the circuit is designed for this family. Interchangeability is most reliable when the amplifier operates within the permitted current draw and when the power transformer and the smoothing network (capacitors/choke) match the intended specifications.

Exceptions can occur in designs with high inrush/peak currents, marginally sized transformers, or a first input capacitor that exceeds what the rectifier is designed to tolerate. In service cases, it is good practice to verify B+ under load, transformer temperature reserve, and compliance of the reservoir capacitor value with the amplifier design.

What about availability, shipping, and spare-part supply in Germany/Europe?

GZ34, GZ34s and 5AR4 are currently in production, which supports practical servicing of guitar amps, hi-fi amplifiers, and tube devices in long-term use.

End customers benefit from clear selection guidance and fast availability, while professional users rely on consistent specifications and predictable re-ordering. International shipping is relevant for export equipment, touring rigs, and globally supported service cases outside Europe.