Tubes

The small-signal triode that became the default high-gain audio tube: compact, cheap, and quiet enough for phono and preamp stages.

Premium and ruggedized variants can be compatible, but noise, heater current, and microphonics still matter in phono stages.

Born as a VHF/cascode tube, the 6DJ8 family migrated into high-end audio because it can be very quiet and fast in low-level stages.

The family has many near-equivalents; heater voltage and operating-point assumptions are not always interchangeable.

The workhorse low-gain dual triode for buffers, drivers, and line stages where current delivery matters more than voltage gain.

A higher-transconductance cousin of the 12AX7, widely used where a circuit needs more drive current or RF-era bandwidth.

An American high-power beam tube adopted by large hi-fi amplifiers that needed more plate dissipation than the classic smaller audio outputs.

Often compared with KT88, but bias and screen limits are circuit-specific.

A rugged, high-current small tube that became strongly associated with modern Audio Research and BAT circuits.

The British high-power audio output tube: a staple for push-pull amplifiers that want large output without abandoning tube character.

Not automatically a drop-in for every 6550 circuit.

One of the canonical octal audio triodes: linear, forgiving, and large enough to be used as a serious driver tube.

The classic European output pentode behind countless British hi-fi and guitar amplifiers: moderate power, high gain, and a long production life.

American 6CA7 beam versions are related but not identical in construction.

The distinctive shouldered modern KT tube used by several reference amplifiers chasing still more plate dissipation and output power.

A sturdier dual triode often chosen as a driver where a 12AU7-type device is not muscular enough.

Originally a telephone repeater/amplifier tube, the 300B became the emblem of single-ended triode hi-fi: low power, high linearity, huge mythology.

A slow-warmup rectifier prized in audio because it is efficient and gentler on power supplies than many older rectifier types.

A miniature dual triode often described as a 6SN7-like device in a nine-pin envelope.

A modern super-sized KT-family output tube that let contemporary tube amps claim substantially more power from familiar push-pull layouts.

A Russian dual triode often treated as its own design rather than a simple Western drop-in, despite superficial 6DJ8 comparisons.

Do not assume 6DJ8/6922 compatibility unless the manufacturer says so.

The classic low-noise audio input pentode, a staple of vintage preamp and microphone-amp front ends.

A compact output pentode that made low-to-medium-power integrated amplifiers practical and affordable.

A twin low-mu, low-plate-resistance power triode built for series voltage regulators, later the canonical output tube of Atma-Sphere and other OTL amplifiers.

The 6080 is the ruggedized industrial equivalent; the Russian 6H13S/6Н13С is close but not always a silent drop-in.

A compact rectifier common in smaller amplifiers and preamp power supplies.

The original American beam power tube family, later stretched into many ruggedized versions and audio/guitar variants.

The high-gain octal partner to the 6SN7, often found in vintage-inspired input and driver stages.

A Russian high-gain dual triode that occupies a similar design niche to 12AX7/ECC83 but uses a different heater arrangement.

Not a direct 12AX7 plug-in in normal Western wiring.

A large transmitting triode pressed into audio service by designers who want single-ended triode sound with more power than a 300B can supply.

Designed for VHF/FM front ends, later borrowed by a few audio circuits for small-signal duty.

A glow-discharge reference tube used to stabilize high-voltage supplies rather than amplify audio.

A small RF pentode occasionally appears in audio as a gain device or in support circuitry.

A high-current triode usually seen in regulated power supplies rather than the audio signal path.

A rugged European dual triode used in instrumentation and, later, boutique audio circuits.

A recent high-power KT-family member aimed at large modern tube amplifiers with suitably designed transformers and bias supplies.

A low-noise dual triode favored in microphone and instrument preamps and quiet line stages; the 6072 is its premium equivalent.

A high-voltage transmitting triode now associated with large, expensive single-ended and push-pull amplifiers.

A workhorse directly-heated full-wave rectifier for tube power supplies.

A TV damper diode sometimes used as a soft rectifier/regulator in tube power supplies.

A dual triode pairing a high-mu and a low-mu section for combined gain and drive in one envelope.

A rare 9-pin (Noval B9A) Japanese power triode by NEC, roughly a 2A3-class triode in a miniature envelope, used in push-pull output of the original Luxman SQ38 family.

A genuine power triode, not a triode-pentode; long out of production and rare.

A smaller beam-power relative of the 6L6, used in compact amplifiers and sometimes as a driver or regulator in hi-fi gear.

A small rectifier frequently seen in modern Chinese tube-output DACs and integrated amplifiers.

A tiny metal-ceramic nuvistor developed near the end of the vacuum-tube era, later revived by Musical Fidelity’s Nu-Vista line.

A TV line-output tube family repurposed by some audio designers because it can tolerate high current and unusual output-stage demands. Its series-heater (40 V/300 mA) sibling is PL509 (US 40KG6); the higher-dissipation EL519/PL519 is a distinct type.

A massive Russian directly heated triode used by a handful of statement amplifiers for high-power triode operation.

A ruggedized computer-service relative of the 12AU7 class, occasionally selected for audio output buffers.

A low-mu triode with strong current capability, popular in OTL/OCL and line-output stages.

A 9-pin twin triode from the FM-tuner era (RF-amp and oscillator-mixer duty) with two dissimilar sections, used as the signal tube in the Leben CS-200p; its 6.3 V-heater equivalent is the 6DT8.

Not an ECC86/6GM8 low-voltage triode; the direct equivalent is the 6.3 V-heater 6DT8.

The 17 V series-string double triode of the ECC85 (6AQ8) VHF family; its identical equivalent is HCC85. Not the 6EW8 (=ECF806, a distinct triode-pentode).

A directly heated rectifier famous mostly through Western Electric and later audio revival circuits.

A classic directly-heated single-ended triode prized for its sweet, low-power output.

A Western Electric pentode revered as a driver for 300B/845 stages and used by makers such as Line Magnetic.

A 12-pin (duodecar) 50 V-heater power triode developed by NEC for audio output, ~30–35 W push-pull; the output tube of the Luxman SQ38F. Its 6.3 V/10 V-heater siblings are the 6CA10/10CA10.

Out of production since the late 1970s and expensive; the 50 V heater means it is not interchangeable with the 6/10 V siblings without rewiring.

A rugged high-current dual triode used as a muscular driver or output buffer.

A tiny, very high-transconductance triode prized in some phono stages for low-level gain.

A classic 5 V directly-heated full-wave rectifier for supplies up to ~125 mA; the "5Y3WGT" is the ruggedized military version with identical electrical characteristics.

A subminiature dual triode used in compact, low-noise, and rugged circuits.

A video output pentode of the 6CL6 family used as a driver in some tube designs.

A triode-pentode used where one envelope must provide both voltage gain and drive.

A compact Russian power/regulator triode often found in tube-regulated power supplies.

A squat, very high-current Russian triode made famous in audio by OTL and SET amplifiers that exploit its low plate resistance.

A very high-transconductance miniature triode used in minimalist high-gain audio stages and phono circuits.

The Soviet 6С5С octal general-purpose triode, a direct equivalent of the American 6C5/6C5GT, used as the driver triode in the Lyrita GM70 monoblock.

Do not confuse with the rectifier 6Ц5С (a kenotron ≈ 6X5GT); the audio type is the 6С5С triode.

A specialist tube used in auxiliary circuitry, not a mainstream audio gain device.

A compact triode-pentode that lets a designer combine gain and driver functions in one envelope.

A high-transconductance (~30 mA/V) Soviet broadband power pentode (Cyrillic 6Э5П); triode-strapped it is a very linear driver — a popular 300B/GM70 driver, as in the Lyrita GM70 monoblock.

A specialist tube seen in support roles in older hybrid designs rather than common hi-fi signal stages.

A UHF triode occasionally used as a low-level gain device in specialized audio circuits.

An uncommon support tube occasionally found in regulated supplies or auxiliary circuits.

A high-current TV sweep tube adopted by some hybrid and OTL audio designs.

A high-current Russian dual triode associated with very expensive modern preamps and power-amp driver stages.

A robust Russian dual triode used where a small-signal tube needs more current capability.

A rugged Russian triode used in voltage-regulation and power-supply roles.

A 6.3 V indirectly-heated octal full-wave rectifier that can share a common heater winding, avoiding a separate 5 V rectifier tap; the European equivalent is EZ35.

A high-transconductance twin triode of the 5687/7119/E182CC family used as a muscular small-signal driver — the driver tube in the Audio Research D-250 (ARCDB mis-transcribes it as "7144", which is not a real tube type).

Another radio transmitting tube adopted by modern single-ended amplifiers for high-voltage, high-power triode operation.

A proprietary Ayon-selected power tube used in the Crossfire; Ayon does not publish the base type.

A special-quality frame-grid pentode, often triode-strapped for very low-noise, high-transconductance audio gain.

A triode-pentode combining a gain triode and a pentode in one envelope, used as a compact gain-plus-driver device. Its US equivalent is 6JW8 (6GJ7 is the distinct ECF801).

A medium-mu triode plus sharp-cutoff pentode in one envelope (US 6U8/6U8A), first for VHF TV/radio, later common in hi-fi input/driver stages such as the Mars Tube Audio Student.

US equivalent is 6U8/6U8A (also 6KD8), not 6X8.

A one-envelope triode-plus-power-pentode (US 6GV8): the triode drives and the beam pentode outputs, as in the single-ended Elekit TU-8185.

A premium low-noise small-signal pentode used where very quiet voltage gain is required.

A high-current sweep pentode (US 6KG6A; series-heater sibling PL519 = US 40KG6A), higher-dissipation than EL509, repurposed by makers such as EAR Yoshino as an audio output valve.

A small 7-pin (B7G) output pentode originally for car radios, giving roughly 3 W single-ended; four power the Atma-Sphere Gem, whose vendor also allows the identical 6DL5 or the near-substitute 6BM5.

GEC beam tetrode of the 6L6 class, prized in classic British amplifiers such as the Quad II.

GEC’s beam-tetrode answer to the EL34 class, valued where a designer wants EL34-scale power with different transfer characteristics.

A later high-power audio tube created for more headroom in KT88-style sockets and popularized by modern valve-amplifier makers.