Knight-kit R-55A

Knight R-55A receiver kit

Allied Radio's Knight kit R-55A receiver was introduced in 1963 as an upgrade to the R-55. The R-55A is a transformer-operated single-conversion general coverage receiver covering 530KHz to 36MHz and 47 to 54 MHz in 5 bands with calibrated bandspread for the 80 to 6 meter ham bands. It sports dual IF amps, BFO, flywheel tuning, and a built-in speaker. The 6 tubes are used very efficiently with a couple of 6AW8A triode/ pentode tubes for dual function.

These radios started life as kits. Kit builders had varying levels of skill. Therefore I recommend checking every soldered connection, tightening all screws especially those used for ground lugs, and giving it a thorough alignment. A frequency counter is handy for checking IFs, oscillator tracking, and to properly set the high and low ends of the bands.

When performing properly, this radio is a fun and easy-to-use SWL receiver. It was also intended as a part of a "First" amateur radio setup. The Knightkit T-60 is the matching ham bands transmitter.

A partial manual can be downloaded from BAMA. See the home page for a link.

Knight-kit R55A receiver


REPAIR NOTES The set had a hum that also distorted the audio. The hum was still present with the volume control turned down. Suspected the electrolytic power supply filter. Bridging a known-good cap did not help. Pulled the rectifier tube. Substituted B+ from my well-filtered Heath PS-4 variable high voltage supply. Hum still present. Suspected possible heater to cathode leakage. Swapping the two 6AW8 tubes did not help. Traced the audio section with an oscilloscope. Found hum signal on the ground connections at the audio preamp tube. Re-tightened the socket screws, but the self-grounding wafer tube socket apparently has a problem. Adding a separate ground wire solved the hum and distortion problems.

As suspected, the alignment was off. With a local broadcast station tuned in at 1340 KHz, my little Radio-Shack frequency counter read 3117 at the oscillator plates on the tuning cap (via the counter's little antenna with an insulated sleeve over it.) That was definitely high. This set has an IF of 1650 KHz so the counter should have read 1340+1650 = 2990. Proceeded to align the IF transformers at the proper 1650. Adjusted the BFO at the same time.

In further alignment checks, found bands A and B to be fairly close with some tweaking needed but the other bands are way off. Suspect the kit builder may not have had the proper equipment so was never able to get full performance from this set.

1-24-02


The project previously on the bench undergoing repairs was the National NC-120 / RAO receiver.



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