Common Tube Types

WARNING! The table below proposes some guidelines for tube substitutions. No guarantee of desirable results is to be presumed, based upon these guidelines. Tube substitution can be a costly activity which can result in damage to other components in the amplifier (including other tubes, resistors, and even transformers) and should be regarded as an experiment. Like all experiments, the desirability of the result is to be judged in the mind of the experimenter. Proceed with caution and don't say I didn't warn you.

ANOTHER WARNING! Tube amplifiers produce, use and store high voltages which may be harmful or even lethal to human beings. Keep your friggin' fingers out of things that you don't know nothin' about.

Common Tubes
Designation Type Common Applications
5U4GA Rectifier Converts A.C. to D.C. in high-power applications.
5U4GB Rectifier Converts A.C. to D.C. in high-power applications. This is a plug-compatible replacement for a GZ34 and can be used to enhance compression/sag in amps that come equipped with the more efficient GZ34. The reverse substitution should be performed with caution as it may result in higher plate voltages reducing the life of other tubes.
5AR4 Rectifier Converts A.C. to D.C. in low-to-medium-power applications.
5Y3 Rectifier Converts A.C. to D.C. in low-power applications. This tube can be used as a plug-compatible replacement for a 5AR4 to enhance compression, but will generally have a shorter life than a 5AR4 in the same application.
5V4 Rectifier Converts A.C. to D.C. in medium-power applications. This tube is plug-compatible with the 5Y3, but has a lower internal impedance and is therefore somewhat more efficient than the 5Y3. Use of a more efficient rectifier will generally make an amplifier louder and brighter. The trade-off is that it will also degrade the amp's compression characteristics. Replacing a rectifier with a more efficient tube can also result in higher plate voltages which can reduce the life of other tubes.
GZ34 rectifier Converts A.C. to D.C. in medium to high power applications.
6SC7 pre-amp Pre-amp tube. Generally found on amps designed before 1955.
12AT7 pre-amp Pre-amp tube.
12AY7 pre-amp Low-gain pre-amp tube. Lower gain characteristics than a 6SC7.
12AX7 pre-amp High-gain pre-amp tube. Higher gain characteristics than a 6SC7.
7025 pre-amp High-gain pre-amp tube. Military version of the 12AX7.
ECC83 pre-amp Like the 7025, this can generally be regarded as another designation for a 12AX7 these days. British amps generally use the ECC83 in places where American manufacturers would use the 12AX7. Although there may be minimal differences in gain characteristics and tone, the two types may generally be considered interchangeable.
6V6GT output Output tube in low to medium power amps, such as the Fender Champ (1 6V6, 5 watts), Princeton (2 6V6s, 12 watts), and Deluxe (2 6V6s, 22 watts). 6V6s can generally be used as replacements for EL84s in amps such as the VOX AC-30 and many amps with a similar design, such as Peavey's Classic 30. The reverse operation should not be performed as the EL84 draws more filament current and can cause failure of the 6.3V filament transformer.
EL84 output Output tube for low to medium power amps, such as the VOX AC-30 and many similar designs.
6BQ5 output The American designation for an EL84. This tube was commonly used in the output stage of Gibson amplifiers.
6L6GC output Output tube in medium to high power amps, including virtually all Fender amps rated above 30 watts. The GC means Glass Case. The earlier 6L6 was the same tube with a metal case.
5881 output This is the military grade version of the 6L6GC. The two types are direct replacements for each other.
6L6GWB output Another designation for the military grade 6L6GC. The two types are direct replacements for each other.
6550 output Output tube for medium to high power amps. The 6550 is a possible replacement for any 6L6 type tube. The 6550 is rated for higher voltages than the 6L6 types, and, when operated at these higher voltages, can produce more power and a cleaner sound than a 6L6 type. It is therefore at its best in applications for bass guitar, keyboards, and steel guitar. The 6550A is an improved version of the 6550.
6550WA output Military grade version of the 6550.
EL34 output Output tube for medium to high power amps, including many Marshal designs in the 45 to 100 watt range.

**Common Tubes**
Designation	Type	Common Applications
5U4GA	Rectifier	Converts A.C. to D.C. in high-power applications.
5U4GB	Rectifier	Converts A.C. to D.C. in high-power applications. This is a plug-compatible replacement for a GZ34 and can be used to enhance compression/sag in amps that come equipped with the more efficient GZ34. The reverse substitution should be performed with caution as it may result in higher plate voltages reducing the life of other tubes.
5AR4	Rectifier	Converts A.C. to D.C. in low-to-medium-power applications.
5Y3	Rectifier	Converts A.C. to D.C. in low-power applications. This tube can be used as a plug-compatible replacement for a 5AR4 to enhance compression, but will generally have a shorter life than a 5AR4 in the same application.
5V4	Rectifier	Converts A.C. to D.C. in medium-power applications. This tube is plug-compatible with the 5Y3, but has a lower internal impedance and is therefore somewhat more efficient than the 5Y3. Use of a more efficient rectifier will generally make an amplifier louder and brighter. The trade-off is that it will also degrade the amp's compression characteristics. Replacing a rectifier with a more efficient tube can also result in higher plate voltages which can reduce the life of other tubes.
GZ34	rectifier	Converts A.C. to D.C. in medium to high power applications.
6SC7	pre-amp	Pre-amp tube. Generally found on amps designed before 1955.
12AT7	pre-amp	Pre-amp tube.
12AY7	pre-amp	Low-gain pre-amp tube. Lower gain characteristics than a 6SC7.
12AX7	pre-amp	High-gain pre-amp tube. Higher gain characteristics than a 6SC7.
7025	pre-amp	High-gain pre-amp tube. Military version of the 12AX7.
ECC83	pre-amp	Like the 7025, this can generally be regarded as another designation for a 12AX7 these days. British amps generally use the ECC83 in places where American manufacturers would use the 12AX7. Although there may be minimal differences in gain characteristics and tone, the two types may generally be considered interchangeable.
6V6GT	output	Output tube in low to medium power amps, such as the Fender Champ (1 6V6, 5 watts), Princeton (2 6V6s, 12 watts), and Deluxe (2 6V6s, 22 watts). 6V6s can generally be used as replacements for EL84s in amps such as the VOX AC-30 and many amps with a similar design, such as Peavey's Classic 30. The reverse operation should not be performed as the EL84 draws more filament current and can cause failure of the 6.3V filament transformer.
EL84	output	Output tube for low to medium power amps, such as the VOX AC-30 and many similar designs.
6BQ5	output	The American designation for an EL84. This tube was commonly used in the output stage of Gibson amplifiers.
6L6GC	output	Output tube in medium to high power amps, including virtually all Fender amps rated above 30 watts. The GC means Glass Case. The earlier 6L6 was the same tube with a metal case.
5881	output	This is the military grade version of the 6L6GC. The two types are direct replacements for each other.
6L6GWB	output	Another designation for the military grade 6L6GC. The two types are direct replacements for each other.
6550	output	Output tube for medium to high power amps. The 6550 is a possible replacement for any 6L6 type tube. The 6550 is rated for higher voltages than the 6L6 types, and, when operated at these higher voltages, can produce more power and a cleaner sound than a 6L6 type. It is therefore at its best in applications for bass guitar, keyboards, and steel guitar. The 6550A is an improved version of the 6550.
6550WA	output	Military grade version of the 6550.
EL34	output	Output tube for medium to high power amps, including many Marshal designs in the 45 to 100 watt range.


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