King KU-193 aircraft band transceiver

Description

Well used King KU-193 aircraft band transceiver. This 4 channel unit contains transmit/receive crystal pairs for 122.7 MHZ. and 125.7 MHZ. as well as a receive crystal for 127.85 MHZ.
The transmit /receive crystals for the switch position marked with 128.85 have been removed. When energized this unit produces sound consistent with a functioning receiver. The background static is muted with partial clockwise rotation of the squelch control as would be expected. No aircraft transmissions were noted, likely due too an improper antenna and /or no local activity on these frequencies. With top cover removed , placing ones hand near to the receive circuit board will incite reception of a powerful AM broadcast band station. This indicates function of the detector and audio circuitry. With top cover in place this overloaded condition is not possible.
Used an antenna tuner that includes a dummy load which can be accessed directly bypassing the tuner elements. Assuming the dummy load is 50 ohm impedance throughout the frequency range the tuner is designed for ( 1.8 - 30 MHZ. ). How reactive it may become at the frequencies of 122 and 125 MHZ. is unknown, but better than nothing. The King transceiver was connected to this metered unit with switches set to bypass the tuner. A tap on the interconnecting coax was routed to a frequency counter. Pressing the "push to talk" switch on the microphone caused deflection of both needles in the dual needle meter on the tuner. The power meter indicates around 10 watts and the SWR meter reads about infinite for both transmit crystals. During transmit the counter indicates the same frequency as stamped on the crystal which has been selected. Whistling into the microphone does not produce the usual power increase with amplitude modulation , possibly indicating a problem. The less than optimal test setup may be suspect here as well. At least it is known that the transceiver is producing RF energy on the expected frequencies. Noting the high SWR reading, never transmitted in excess of 10 seconds at a time. The transceiver draws approx. 10 watts during receive and 50 watts during transmit.
No heat stressed components are visible within the unit , although one filter capacitor appears to have been replaced. The attached microphone is manufactured by Astatic , but marked "King" so is likely O.E.M.