ECHO 'Range King' Base Station RF Amplifier

Echo Communications "Range King" uses two 6JG6 tubes in GG mode at 850VDC and 6BQ5 keyer.
Covers 25-40MHz.
Input power 120VAC.
Safe output rating: 17W AM, 68W average, 80W PEP SSB.
(Note: Due to the peculiar HV keying arrangement, these have a nasty failure mode of putting a momentary 350V spike on the input coaxial line from the transmitter when the keyer releases. Although it might not damage a tube tranceiver it can fry a solid state one.)

not for sale. not for use on CB band. for educational display only.

Details:
Two 6JU6 in parallel produce 80W PEP output on SSB. Green lamp is pilot, amber is RF current indicator. Black switch is power on/off, red switch is standby. Power supply input is 117VAC. The transformer secondary uses a full wave bridge supplying 680VDC. In standby, the negative side of the power supply is disconnected from ground. Unit uses an unusual keying scheme. The keyer uses a relay connected from the otherwise unused center tap of the power transformer (340VDC) to the plate of a 6BQ5. The cathode of the 6BQ5 returns to ground through a 68 ohm 2-watt resistor. The RF input signal is connected to the control and screen grids of the 6BQ5 so that when an input signal is applied, the 6BQ5 conducts and activates the relay. The rear panel is punched for a pair of inverter transistors - evidence that there is a 12VDC mobile version of this unit as well. The hole patterns are above the rear label and are sized for TO-36 case Germanium switching transistors as were used in power inverter circuits. The frequency range of the amplifier is shown to be wide, but in order to achieve this range efficiently, it is necessary to tap the PI-network coil. It can be put on 6M, but efficiency will suffer and the RF current pilot lamp coil should be reduced to 2 turns.