KT66
| KT66 | |
|---|---|
Original G.E.C./M.O.V. version of the KT66 Beam-Power Tetrode tube; this is an example from late production
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|
| Classification | Beam-Power Tetrode |
| Service |
Class-A amplifier, (single-ended) |
| Cathode | |
| Cathode type | Indirectly heated |
| Heater voltage | 6.3 |
| Heater current | 1.27A |
| Anode | |
| Max dissipation Watts | 50 |
| Max voltage | 500 |
| Socket connections | |
|
Octal Base, (IO)
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|
| Typical class-A amplifier operation | |
| Anode voltage | 250 |
| Anode current | 85mA |
| Screen voltage | 250 |
| Bias voltage | −15 |
| Anode resistance | 22K Ohms |
| Typical class-AB amplifier operation (Values are for two tubes) |
|
| Anode voltage | 400 |
| Anode current | 62.5mA (Includes Screen Current) |
| Screen voltage | 400 |
| Bias voltage | −38, (Class AB1) |
| References | |
|
Super Radiotron Valve Manual, Amalgamated Wireless Valve Co. Australia, June 1962 |
|
Class-A amplifier, (single-ended)
Super Radiotron Valve Manual, Amalgamated Wireless Valve Co. Australia, June 1962
KT66 is the designator for a beam tetrode vacuum tube introduced by Marconi-Osram Valve Co. Ltd. (M-OV) of Britain in 1937.
The KT66 is the direct 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 be 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 deflect 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" in the lower parts of the tetrode's voltage-current characteristic curves (which sometimes caused tetrode amplifiers to become unstable), M-OV marketed this tube family as the "KT" series, standing for "kinkless tetrode".
A number of different KT tubes were later marketed by M-OV. Some, but not all, were versions of existing American beam tetrode tubes or European power pentodes, such as the KT66 (6L6), KT77 (EL34 and 6CA7), KT88 (6550), and KT63 (6V6).
Although the RCA 6L6 of 1936 (the result of a license agreement between RCA and M-OV) was the first true "beam power tube" on the market, the later KT66 became almost equally famous, at least in Europe. The two tubes were nearly interchangeable, except that the KT66 was somewhat more rugged than the early metal 6L6.
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Wikipedia