1445477 Oscillators; transistor amplifying circuits STANDARD TELEPHONES & CABLES Ltd 3 Dec 1974 52247/74 Headings H3F and H3T An arrangement for controlling the output of an oscillator using a magnetically-beamed valve 2, Fig. 1, comprises a rectifier 1 for coupling to a control grid of the valve and a differential amplifier 14 controlling the catching voltage of the rectifier 1, a first input of the amplifier being connected to a manually adjustable reference potential source 21 for setting the power output level and the other input to a feedback connection, i.e. resistors 25, 26, from the rectifier 1 stabilizing the catching voltage. In the embodiment amplifier 14 is coupled to the cathode 4 of diode 1 via emitter-follower 13 and commonemitter coupled transistor 6, further negative feedback being applied around amplifier 14 and emitter-follower 13 by means of resistor 23 and capacitor 24. In a modification, an additional differential amplifier provides at its output the input to the first input of the first amplifier, one input of this additional amplifier being connected to the manually adjustable reference source and the other, to which local negative feedback is applied, providing a point to which an external feedback signal can be applied to compensate for an oscillator parameter, e.g. anode current, r.f. tank circuit voltage, r.f. load current or load temperature (Fig. 2, not shown). The common-emitter coupled transistor may be replaced by a pair of transistors in parallel (Fig. 3a, not shown) or a cascade circuit in which the upper transistor is replaced by a Darlington pair 66SP1/SP, 6b, Fig. 3b, may be used; the transistor 6b may be protected against overvoltage by means of a diode 35.
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