6L6
| 6L6 | |
|---|---|
Pair of 6L6GC tubes:
Left: General Electric version from 1960s Right: current manufacture from Svetlana Electron Devices |
|
| Classification: | Beam power tetrode |
| Service: | Class-A amplifier, class-B amplifier, class-AB amplifier, (audio amplifiers) |
| Height: | 4.25 in (108 mm) |
| Diameter: | 1.438 in (36.5 mm) |
| Cathode | |
| Cathode type: | Indirectly heated |
| Heater voltage: | 6.3 |
| Heater current: | 900 mA |
| Anode | |
| Max dissipation Watts: | 30 |
| Max voltage: | 500 Specification listed is for type the type 6L6-GC |
| Socket connections | |
|
Pin 1 – n.c |
|
| Typical class-A amplifier operation | |
| Anode voltage: | 350V |
| Anode current: | 54mA |
| Screen voltage: | 250V |
| Bias voltage: | −18V |
| Anode resistance: | 5k Ohms |
| Typical class-AB amplifier operation (Values are for two tubes) |
|
| Power output: | 55W |
| Anode resistance: (anode to anode) |
5,6k Ohms |
| Anode voltage: | 450V |
| Anode current: | 2*54mA |
| Screen voltage: | 400V |
| Bias voltage: | −37V |
| References | |
| Essential Characteristics, General Electric, 1973 | |
Pin 1 – n.c
Pin 2 – Heater
Pin 3 – Anode (Plate)
Pin 4 – Grid 2 (Screen)
Pin 5 – Grid 1 (control)
Pin 6 – n.c
Pin 7 – Heater
6L6 is the designator for a vacuum tube introduced by Radio Corporation of America in July 1936. At the time Philips had already developed and patented power pentode designs, which were fast replacing power triodes due to their greater efficiency. The beam tetrode design of the 6L6 allowed RCA to circumvent Philips' pentode patent.
The 6L6 is a descendant of the "Harries Valve" developed by British engineer J. Owen Harries and marketed by the Hivac Co. Ltd. in 1935. Harries is believed to have been the first engineer to discover the "critical distance" effect, which maximized the efficiency of a power tetrode, by positioning its anode at a distance which is a specific multiple of the screen grid-cathode distance. This design also minimized interference of secondary emission electrons dislodged from the anode.
EMI engineers Cabot Bull and Sidney Rodda improved the Harries design with a pair of beam plates, connected to the cathode, which directed the electron streams into two narrow areas and also acted like a suppressor grid to redirect some secondary electrons back to the anode. The beam tetrode design was also undertaken to avoid the patents which the giant Philips firm held on power pentodes in Europe. Because this overall design eliminated the "tetrode kink" (negative resistance) in the lower parts of the tetrode's voltage-current characteristic curves, which sometimes caused tetrode amplifiers to become unstable, MOV (Marconi-Osram Valve, a subsidiary of EMI jointly owned with General Electric Company plc) marketed this tube family under the sobriquet "KT", meaning "kinkless tetrode".
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