KT66
KT66 has no equivalent designation confirmed by the archive. Completed sales put the typical price at $111.87 per tube.
The KT66 is a beam pentode with a 6.3 V indirectly heated cathode, intended for audio output stages. It is constructed with an International Octal base and a dome-top tubular bulb, and has no internal or external screening fitted. The tube may be operated in any position.
Ratings and characteristics
The KT66 has a heater current of 1.27 A at 6.3 V. Maximum anode dissipation is 25 W, and maximum screen grid dissipation is 3.5 W. At an anode voltage, screen grid voltage, and control grid voltage of 250 V, 250 V, and −15 V respectively, the anode impedance is 22.5 kΩ and the transconductance is 6.3 mA/V. Interelectrode capacitances are 16 pF for control grid to all other electrodes, 11.5 pF for anode to all other electrodes, and 1.1 pF for anode to control grid.
Operating recommendations
The datasheet recommends a series resistor of 100–300 Ω close to the screen grid terminal to prevent parasitic oscillation, and a control grid series resistor of 10–50 kΩ. The maximum permissible D.C. resistance between control grid and cathode is 0.5 MΩ for auto-bias and 0.1 MΩ for fixed bias. The tube is stated to be intended for push-pull Class AB1 pentode connection with fixed bias, and the datasheet also provides operating conditions for push-pull Class AB1 pentode connection with cathode bias, push-pull Class AB1 triode connection, and single-valve Class A operation.
| Measure | Per tube |
|---|---|
| Median | $111.87 |
| Typical range (25th–75th) | $68.23 – $199.46 |
| Most sales (10th–90th) | $49.26 – $248.75 |
| Extremes incl. outliers | $12.25 – $452.77 |
| Completed sales | 134 |
| Brand | Median | Range | Sales |
|---|---|---|---|
| Genalex/Gold Lion | $124.25 | $89.73 – $187.00 | 43 |
| GEC | $247.50 | $149.50 – $250.00 | 26 |
| GE | $68.23 | $62.72 – $93.53 | 11 |
| Marconi | $104.99 | $80.91 – $197.84 | 9 |
| Mullard | $191.13 | $151.43 – $215.75 | 8 |
| Sovtek | $46.70 | $46.70 – $59.75 | 3 |
| Osram | $140.86 | $111.20 – $354.32 | 3 |
| Philips | $126.35 | $66.00 – $126.35 | 3 |
| RCA | $69.21 | $59.00 – $106.00 | 3 |
| Condition | Median | Sales |
|---|---|---|
| NOS | $96.61 | 34 |
| used | $125.89 | 58 |
| current | $68.77 | 11 |
Per-tube prices from completed sales, 2026-01-27 to 2026-09-03. Matched pairs and quads are divided out. See the price index for how these move over time.
Original manufacturer datasheets for KT66, hosted by Frank Philipse's Electron Tube Data sheets.
| Manufacturer | Designation | Datasheet |
|---|---|---|
| Marconi | KT66 | PDF (569 KB) |
| M-O Valve | KT66 | PDF (409 KB) |
| Marconi | KT66 | PDF (142 KB) |
Documents held here and used to write this page.
- BEAM PENTODE 6-3V INDIRECTLY HEATED