The Johnson Viking Ranger
by Greg Latta, AA8V

Final Tank Circuit Schematic Diagram and Circuit Description

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Introduction:
The Johnson Ranger uses a pi-network for the final tank circuit to match the high impedance of the final amplifier tube to the low impedance of the antenna. The pi-network is ideally suited for this purpose because it allows for a wide range of adjustment and attenuates undesirable higher harmonics that can cause television interference (TVI).

One of the distinctive features of the Johnson Viking Ranger is tank coil L11A. Most tank coils consist of a continuous coil with taps, but in the Viking Ranger gaps are used between the various coil sections to minimize losses in the final tank circuit.

Another distinctive feature of the Viking Ranger is the manner in which the final tuning and antenna coupling are controlled. Rather than use a single variable capacitor each for the final tuning (plate) and coupling (load) capacitors, the designers at Johnson used a combination of variable capacitors and fixed capacitors. The combination approach is preferable, though more expensive, because it permits much finer adjustment of the final tank circuit than is possible when only variable capacitors are used. After using the Ranger for a while one can get spoiled by the ease with which the Ranger can be tuned. The combination approach also permits the settings of the final tank controls (Final, Auxiliary Coupling, and Coupling) to be easily recorded so that the controls can be preset to their approximate positions when changing bands. A slight touch up of the final tuning control to dip the final amplifier current is all that is usually needed after changing bands.

Final Tank Circuit
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Final Tank Circuit:

Plate Coupling Capacitor: RF appearing at the plate of the final amplifier tube must be fed to the output tank circuit, but the DC plate voltage must not be allowed to pass through. The plate coupling capacitor C37 allows the RF to pass through while blocking the DC. This capacitor must be able to handle much more than just the nominal DC plate voltage (500V) on the final amplifier tube. With 100% modulation, the peak voltage on the plate of the final amplifier tube is 4 times the DC plate voltage, or 2000V, so this capacitor must be rated for at least 2000V.

Final (Plate) Tuning Capacitor: Variable capacitor C8A tunes the final tank circuit to resonance on the 20m - 10m bands. This control is normally adjusted for minimum final plate current. On the 40m, 80m, and 160m bands, extra capacitance is switched in by the front section of the bandswitch. Switching in extra fixed capacitance is preferable to using a single variable capacitor because it slows down the tuning rate on the higher frequency bands and makes the final tank circuit easier to adjust.

Extra Final (Plate) Capacitors For 40m: Capacitors C38A and C38B are in series and form a 75pf capacitor. These capacitors are switched out by the front section of the band switch on all bands except 40m. On 40m they are switched in parallel with the final tuning capacitor C8A to provide the extra capacitance needed to tune 40m. Note: These capacitors are connected to C8A through the 10m section of the final tank coil L11A. The reactance of this section of the coil is so small on 40m that it is essentially a short circuit on 40m and has no effect on the connection.

Extra Final (Plate) Tuning Capacitor For 160m and 80m: Capacitors C39A and C39B are in series and form a 150pf capacitor. This combination is then placed in parallel with variable capacitor C8B to form a variable capacitor with a maximum capacitance of 270pf. On 80m and 160m this combination is switched in parallel with the final tuning capacitor C8A by the front section of the band switch to provide the extra capacitance needed to tune 80m and 160m. Note: These capacitors are connected to C8A through the 10m section of the final tank coil L11A. The reactance of this section of the coil is so small on 80m and 160m that it is essentially a short circuit on these bands and has no effect on the connection.

10m - 80m Tank Coil: Tank coil L11A is one of the distinctive features of the Johnson Viking Ranger. Most tank coils consist of a continuous coil with taps, but in the Viking Ranger gaps are used between the various coil sections to minimize losses in the final tank circuit. As the band switch is rotated clockwise from the 80m position to the 10m/11m position, sections are progressively shorted out by the front section of the bandswitch, lowering the inductance.

Extra 160m Tank Coil: Extra inductance is needed to tune the 160m band, and this is provided by tank coil L11B, which is switched in when the bandswitch is rotated counterclockwise from the 80m position to the 160m position. Note that both L11A and L11B are used on 160m. It is the total inductance of L11A and L11B in series that is used on 160m.

Variable Coupling (Load) Capacitor: The coupling (load) capacitance of the final tank circuit is the total capacitance of coupling capacitor C9 and the auxiliary coupling capacitance in parallel. Switching in extra fixed capacitance is preferable to using a single variable capacitor because it permits the use of a smaller variable capacitor and slows down the tuning rate, making the final tank circuit easier to adjust and reset when changing bands.

Auxiliary Coupling (Load) Switch: The auxiliary coupling capacitance is in parallel with the variable coupling (load) capacitor. A seven position switch switches in/out extra capacitance as shown in the table below:  Position  Extra Capacitance (pf)  1  1600  2  1300  3  1000  4  700  5  400  6  150  7  0 Note that the difference in capacitance between the switch settings is less than the maximum capacitance of the variable coupling (load) capacitor. By varying the settings of the coupling and auxiliary coupling controls, the coupling (load) capacitance can be precisely varied from a minimum of about 20pf to a maximum of 1960pf. Switching in extra fixed capacitance is preferable to using a single variable capacitor because it permits the use of a smaller variable capacitor and slows down the tuning rate, making the final tank circuit easier to adjust and reset when changing bands.

Band Switch Front: The front section of the bandswitch switches in and out extra final (plate) tuning capacitance. On the 160m and 80m bands, an extra series/parallel combination of two fixed capacitors and a variable capacitor is switched in to provide the extra capacitance needed to tune these bands. On 40m, extra capacitance is needed, but less than on 160m and 80m. On 40m, a series combination of two fixed capacitors is switched in to provide the extra capacitance needed to tune 40m. On 20m and above no extra capacitance is needed, and none is switched in. On 11m, this section of the bandswitch also shorts out L11B, the extra 160m tank coil.

Band Switch Rear: The rear section of the band switch progressively shorts out more and more of tank coil L11A/L11B as the bandswitch is rotated clockwise. This decreases the inductance, raising the resonant frequency of the final tank circuit. Note: even though the unused sections of L11A/L11B are shorted for DC, the reactance of the shorted sections prevents any RF current from flowing through them. In addition, the special construction of the tank coil minimizes any losses in the final tank circuit.

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