KT150 Power Tubes

KT150 Tung-Sol has a massive plate dissipation of 70 watts, the Tung-Sol KT150 is the most powerful octal beam tetrode ever produced.

Matched Pairs, Quads or Singles

Evatco sells singles, matched pairs and matched quads of KT150. Remember you will need matched pairs or quads when replacing all but single tubes in your amplifiers. Once purchased you may need your amplifier power tubes to be biased to ensure the longest life from your tubes whilst providing the best sound. Whilst some systems provide a bias function, often you will require the help of a technician to bias your tubes. A pair of KT150's can allow an amplifier with a power output approaching 300 watts to be built.

Glass Tube Style

The Tung-Sol KT150 glass envelope is a special egg-shaped balloon that was developed to improve thermal dissipation and maintain a superior vacuum for the best sound. The fact that the glass envelope has no flat sides means the Tung-Sol KT150 has no problems with microphonics.

Not only a powerful, reliable and top performing tube but a sexy tube to look at as well.

Tung-Sol KT150: the most powerful octal power tube ever made

The KT150 is Tung-Sol's flagship beam tetrode and the biggest member of the KT88 family. With a 70-watt plate dissipation rating, it gives designers more headroom than any other octal output tube. Tung-Sol rates a push-pull pair for amplifiers of up to around 200 watts, and well-built designs can approach 300 watts.

Its egg-shaped glass envelope is more than a looker. The curved bulb spreads heat more evenly and helps hold a hard vacuum, and with no flat glass panels it is very resistant to microphonics.

How does the KT150 sound?

In amplifiers designed for it, owners and reviewers consistently describe:

• Deep, controlled bass with real weight and authority
• Big dynamics and effortless headroom at high volume
• Extended, airy treble and a wide, deep soundstage
• A clean, linear midrange that is less coloured than a KT88 or KT120

New KT150s can sound slightly bright and "hi-fi" at first. Many owners report they settle and sweeten noticeably after roughly 200 to 300 hours of use, so give a new set time before judging it.

Tested and matched in Brisbane

Every KT150 we sell is tested on our own equipment before dispatch. Pairs and quads are matched on plate current (Ip) and transconductance (Gm), so each side of your output stage draws evenly and your amp is easier to bias.

• Single: to replace one failed tube in a set
• Matched pair: for most stereo push-pull integrated amps and monoblocks with two output tubes
• Matched quad: for amps with four output tubes (two per channel) or a pair of monoblocks

Is the KT150 right for my amplifier?

Please check before you buy. The KT150 fits a standard octal socket, but it is not a guaranteed drop-in for amps built for the KT88, 6550 or KT120:

• Bias range: the KT150 needs less negative grid voltage for the same plate current. In amps not designed for it, the bias control can run out of range, leaving the tubes running hot. That can shorten their life and risk the output transformer.
• Power supply: it draws more current than a KT88 or KT120, which adds load to the power transformer.
• Physical size: it is taller and wider than a KT88 and may not fit under standard tube cages.
• No free power: in an amp designed for KT88 or KT120, a KT150 won't add meaningful output. The extra power only comes with a circuit and transformers built to use it.

Some manufacturers explicitly say not to fit KT150s to their older KT120 or 6550 models. Fit KT150s only if your amplifier's manufacturer approves them, or a qualified technician has confirmed the amp can bias them correctly. Not sure? Email us your amplifier's make and model and we'll help.

Amplifiers that use the KT150

The KT150 is fitted as standard, or offered as a factory option, in amplifiers including:

• Audio Research Reference 160S, Reference 160M and Reference 75 SE
• VAC Phi 170, Signature 200 and Master 300
• PrimaLuna EVO-series integrated amplifiers
• Weston Acoustics Topaz Duo monoblocks (Australian-made)

Fitting and biasing

New power tubes always need their bias checked. Some amps have auto-bias or a front-panel bias meter; others need a technician. Never fit power tubes with the amp switched on, and let new tubes warm up for a few minutes before setting bias. Valve amps hold lethal voltages even when switched off, so if you're unsure, use a qualified technician.

Tung-Sol KT150 specifications

Download the Tung-Sol KT150 datasheet (PDF)

See also our Tung-Sol KT120 and our full power tube range.