Tung-Sol KT120 - precision matched
Manufacturer: Tung-Sol (reissue)
With 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.
KT120 substitution notes
Price is for a single tube and includes burn-in and standard matching service. Tubes ship in Tung-Sol retail boxes.
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 for 48 hours and tested on a laboratory grade Amplitrex AT1000 tube tester. We match tubes for both current draw (mA) and transconductance (Gm) at typical operating conditions (see #3 below) for no extra charge. We can also custom match power tubes at whatever specifications you provide (see #4 below).
The questions listed below allow you to provide optional information about your operating conditions that will help us select the best matched set of power tubes for your amplifier.
Why this matters
1. What is the manufacturer and model of your amplifier?
2. How is your amp biased? Why we ask
3. Choose the matching option you prefer: Why we ask
4. CUSTOM MATCHING ONLY: If you chose "Custom Match" above, please enter the power tube specifications for your amp
5. Feel free to provide more information (for example, guitarists may want to specify early or late breakup) in the comments section when you check out. Thank you!
Price per single tube: $44.00
Enter total number of tubes needed for your matched set
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.