Patent GB-812324-A (GB)
Title: Radio-frequency amplifier coupling devices
Inventor: SMITH FREDERICK WARREN
IPC: H01P5/10
Filed: 1957-10-28
Abstract: 812,324. Valve amplifier circuits. MULLARD Ltd. Oct. 28, 1957, No. 33545/57. Class 40 (6). [Also in Group XL (b)] A device for coupling a balanced push-pull amplifier to the unbalanced input of the single valve comprises a Lecher line connected at one end to the output terminals of the push-pull amplifier and surrounded at the other end by quarter-wave tubular choke section the tube having an end wall in which the single valve is disposed and connected to its grid, one conductor of the line being connected to the cathode of the valve and the other to a point on the end wall adjacent the valve. In Fig. 1 a push-pull amplifier VA is coupled to the input of a valve VB by a Lecher line F1, F2 in which blocking capacitors C1 and C2 are inserted. The remote end of conductor F2 is formed by part of the outer conductor of a concentric line C feeding current to the heater of the single valve VB. This end of the line is surrounded by a quarterwave tubular member K connected to the line by an end plate L in which the valve VB is disposed. It is explained that the circuit from the upper anode of valve VA to earth includes the shorted quarter-wave line and therefore constitutes a high-impedance circuit. The circuit from the lower anode includes part of the line F2, the part J of the outer conductor of the concentric line C and the return connection from the outer conductor to the cathode of valve VA and this is also dimensioned so as to have a high impedance. A stub line A projecting either into the interior of the tube K or in the reverse direction or at right angles to the line is provided and by adjusting metallic tuning slugs B and E the output of the amplifier VA may be matched to the input of VB. A further line G is provided through which the high tension is fed to the anodes of valve VA. Figs. 4 and 5 show plan and side views of the structure of the arrangement. The Lecher line A1, A2 connecting the push-pull valve VA to the valve VB is provided with two overlapping parts at C1, C2 separated by mica spacers to form the blocking capacitors. The valve VB is mounted in an eccentric aperture in the end wall L of the quarter-wave tube K and the conductor A1 of the Lecher line is connected to the end wall. A further tube 40 surrounds the quarter wave tube and forms part of an anode-grid cavity resonator for the valve. A1 (Fig. 5) constitutes the stub line and the slug B is mounted on a screw-threaded rod 25 supported in an insulated block 26 rotation of the slug, which is of silvered brass, is prevented by two nylon studs 27 secured to the slug. The slug E (Fig. 4) is variable in a similar manner. Line G (Fig. 5) is the H.T. feed line and J the heater supply line. The output from the single valve is derived from a probe 20 and the output cavity is tunable by a plunger Z (Fig. 4). The tuning slug E could alternatively be placed at the opposite end of the Lecher line or an additional slug could be provided in that position. It is also stated that elliptical or polygonal members could replace the circular cylindrical members K and D.