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Tung-Sol KT120 - precision matched

Tung-Sol KT120 - premium matched
Manufacturer: Tung-Sol (reissue)
Tung-Sol KT120With a plate dissipation of 60 watts, the Tung-Sol KT120 is the most powerful tube in the 6550/KT88/KT90 family. A pair of these tubes in push-pull configuration can deliver power levels of 150 Watts or more. When it's run in circuits designed for 6550/KT88/KT90 tubes, the KT120 resists being overdriven and reliably delivers peak power. (View KT120 spec sheet and curves.)

The KT120 has a taller glass bottle, longer internal plate structure, and much larger control grid cooling fins than current production KT88 tubes. Because the KT120 draws 100-300 mA more filament current than a standard 6550/KT88, check with your amp manufacturer to ensure you have the additional filament headroom to power these tubes. This new production Tung-Sol tube is manufactured in Russia for New Sensor.

These tubes have been burned in, tested at typical operating voltages on a laboratory grade Amplitrex AT1000, and precisely matched for both current draw (mA) and transconductance (Gm). Learn more about our burn-in and testing process here.

Price is for a single tube and includes burn-in and standard matching service. Tubes ship in Tung-Sol retail boxes.

KT120 substitution notes

The KT120 tube is one of the more exciting developments in new production vacuum tubes. Generally speaking it is a drop in replacement for 6550, KT88 and KT90 tubes, as long as the larger bottle fits in your chassis. This tube also draws more filament current
(100-300 mA more per tube) than 6550/KT88/KT90 tubes do, so you need to be sure your power supply can handle the increased demand.

Many people report improved bass response and increased output with KT120 tubes. The reason for this stronger response is obvious when you look at its test results. New production 6550 and KT88 tubes we test range from 90-140% of the expected value for mA and Gm. Under the exact same operating conditions (500v plate, 300v screen, -30.5v bias) the KT120 rarely tests lower than 125% and can test as high as 185%. (We reject KT120 tubes that test higher than 165%--at some point you have to say enough is enough!)

Most fixed bias amps have enough range to dial KT120 tubes in to the recommended current draw for that amplifier, though some do not. Even if you are unable to bias the tube all the way down to the recommended current draw you can probably still use KT120 tubes. You'll just have to do a little math to be sure the tubes are running safely. Simply take the plate voltage and multiply it by the current measured in mA. For example, if your plate voltage is 500v and you are measuring 70 mA across a single tube then the math goes like this 500 x 0.070 = 35 Watts. Since this is a 60 watt dissipation tube and the rule of thumb is to run tubes at 65% of their maximum dissipation (60 x .65 = 39 Watts), 70 mA across a single tube in this case would be just fine even though the manual is likely to recommend 50 mA for a 6550 tube.

If you have an autobias amplifier you will want tubes at the lower end of the spectrum of KT120 tubes.

Please email or call us if you'd like our help deciding if the KT120 tube is a good fit for you.

Precision Power Tube Matching

Our power tubes are burned in and then tested on a laboratory grade Amplitrex AT1000 tube tester. We match tubes for both current draw (mA) and transconductance (Gm) at typical operating conditions (plate: 500V, screen: 300V, grid bias: -30.5V).

After burn in and testing, we hand select and custom match every power tube order we receive. To do this, each power tube set is also run on a custom, fully variable test fixture that can match the operating conditions of your amplifier based on the information you provide below. This enables us to do a final check of the power tube set's performance and matching under load. Why this matters
1. What is the manufacturer and model of your amplifier?
2. How is your amp biased?   Why we ask
3. Matching notes   Why we ask
If you know the plate, screen, and grid bias voltages your amplifier uses, please note them in the comments section when you check out and we will use this information when we select and match your power tube set. (If you don't know, don't worry--we can make an educated guess based on your amp's make and model, if we don't already know the voltages it uses.) If you are a guitarist, you can also specify if you prefer early or late breakup. Thanks!


Price per single tube: $48.00

Enter total number of tubes needed for your matched set

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TC Tubes specializes in precision testing and matching of vintage and new production vacuum tubes for guitar & bass players, audiophiles, and DIY tube audio enthusiasts. Our website features secure payment options and fast, convenient shipping around the world.

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