Tube Amp Doctor (TAD) KT88-STR Power Tube

Brand: Tube Amp Doctor
Product Code: TAD-RT891
Warranty: 6 Months
Premium Matching: *

$149.00 - $1,192.00
Tube Amp Doctor
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Our Favourite Tube in the KT88 / 6550 Class

The latest version of our TAD KT88-STR is built in the style of the early British MOV KT88. It has the same big and heavy glass envelope and beautifully polished metal base. Its wonderful tone and great appearance make this tube the most attractive choice for high-end audio applications and powerful bass guitar amps.

It offers a vivid and three-dimensional tone, pleasingly warm, detailed and with subtle highs. A very musical reaction, with great sound and finest details in mids and top-end; a linear and harmonious overall response with a very natural tone, make the TAD KT88-STR our favourite tube in the KT88 and 6550A class.

TAD Premium Selection

Q: When does a power tube become a Premium Selected power tube?

A: All power tubes labelled Premium Selected have passed the following tests:

  • Plate Current (PC) and Amplification (TC)
  • Low Noise Test
  • Microphonic Test
  • Sonic Test
  • Shock Test
  • Listening Test
  • Shorts & Leakage Test

Premium RT-Matching of Power Tubes

Our Premium Matching is an exact matching of power tubes with identical Plate Current (PC) and Transconductance (TC).

Electrical Characteristics
Heater Voltage (AC or DC) Minimum: 5.8 V, Nominal: 6.3 V, Maxium: 6.8 V
Heater Current 1.6 A
Cathode Oxide-Coated, Unipotential
Cathode-to-Heater Potential, Max. 250 V
Direct Interelectrode Capacitance, Max.* Grid No. 1 to Cathode and Grid No. 3, Grid No. 2, Base Sleeve and Heater: <17.0 pF / Plate to Cathode and Grid No. 3, Grid No. 2, Base sleeve and Heater: <12.0 pF / Grid No. 1 to Plate: <1.3 pF

* Without external shielding, nominal values.

Operating Position Vertical
Base Octal, 8-Pin
Dimensions - Height 114 mm (4.488”)
Dimensions - Seated Height 103 mm (4.055”)
Dimensions - Diameter 52 mm (2.047”)
Cooling Convection
Approximate Net Weight 90 g (3.17 oz.)
AF Power Amplifier Maximum Ratings
DC Plate Voltage 800 V
Grid No. 2 DC (Screen) Voltage 600 V
Grid No. 1 DC (Control) Voltage -300 V
DC Cathode Current 230 mA
Plate Dissipation 42 W
Grid No. 2 DC (Screen) Dissipation 8 W
Plate + Grid 2 Dissipation 46 W
Bulb Temperature (Surface Hottest Point) 250° C
Typical Operatation - AF Power Amplifier, Class A1 (Single Tube)
Plate Voltage 400 V
Grid 2 Screen Voltage 225 V
Grid 1 Control Voltage** -16.5 V
Peak AF Grid 1 Control Voltage 16.5 V
Zero Signal Plate Current 87 mA
Maximum Signal Plate Current 105 mA
Zero Signal Grid 2 Screen Current (Avg.) 4 mA
Transconductance (Nominal) 9,000 mS
Load Resistance 6 kΩ
Output Power at 5% Distortion 19 W

** Approximate value (set to zero signal plate current).

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