KT77
KT77 has no equivalent designation confirmed by the archive. Completed sales put the typical price at $59.74 per tube.
The KT77 is a beam tetrode vacuum tube with an International Octal base (B8-0) and a tubular bulb. It is designed for use in the output stage of an audio-frequency amplifier, primarily under ultra-linear conditions.
Construction and Ratings
The KT77 has a heater voltage of 6.3 V and a heater current of approximately 1.4 A. Its maximum overall length is 113 mm, maximum seated length is 99 mm, and maximum diameter is 33 mm. The tube may be mounted in any position.
Absolute maximum ratings include a DC anode voltage of 850 V, a DC screen voltage of 650 V, an anode dissipation of 32 W, a screen dissipation of 6.0 W, and a combined anode and screen dissipation of 35 W. Design maximum ratings are 800 V DC anode voltage, 600 V DC screen voltage, 25 W anode dissipation, 6.0 W screen dissipation, and 28 W combined anode and screen dissipation. For tetrode connection, the fixed screen supply must not exceed 300 V.
Characteristics and Life
In typical operating conditions with a DC anode and screen voltage of 250 V, the KT77 has a mutual conductance of 10.5 mA/V, an internal anode resistance of 23 kΩ, and an amplification factor of 11.5. The M-OV datasheet provides these characteristics.
When operated at absolute maximum ratings, the average life expectancy of the KT77 is at least 5,000 hours. At a reduced absolute rating of combined anode and screen dissipation (Pa+g2) of 25 W, the life is at least 10,000 hours.
Applications
Two KT77 valves in Class AB1 give a continuous output of over 70 W. The KT77 is also suitable for use as a series valve in a stabilised power supply.
| Measure | Per tube |
|---|---|
| Median | $59.74 |
| Typical range (25th–75th) | $43.75 – $133.50 |
| Most sales (10th–90th) | $20.83 – $299.99 |
| Extremes incl. outliers | $13.99 – $1,544.95 |
| Completed sales | 29 |
| Brand | Median | Range | Sales |
|---|---|---|---|
| Genalex/Gold Lion | $59.74 | $49.02 – $133.22 | 13 |
| JJ | $32.16 | $30.15 – $44.99 | 4 |
| Mullard | $213.75 | $118.50 – $1,544.95 | 4 |
| Condition | Median | Sales |
|---|---|---|
| NOS | $126.00 | 6 |
| used | $283.51 | 4 |
| current | $45.13 | 16 |
Per-tube prices from completed sales, 2026-06-01 to 2026-09-05. Matched pairs and quads are divided out. See the price index for how these move over time.
Original manufacturer datasheets for KT77, hosted by Frank Philipse's Electron Tube Data sheets.
| Manufacturer | Designation | Datasheet |
|---|---|---|
| M-O Valve | KT77 | PDF (503 KB) |
| JJ | KT77 | PDF (128 KB) |
Documents held here and used to write this page.
- Genalex