ARC-5 WWII Receiver - January 2022 Short Subjects!
Channel: Nashoba Valley Amateur Radio Club (NVARC) / N1NC
Date: 27/01/2022

Rod, WA1TAC, described his recent work on restoring a WW2 era radio, the BC-455 covering 6 to 9.1 MHz.  He had begun this work several years ago on a unit that had suffered multiple 'undocumented modifications'.  Early work included replacing the wax-paper 'flower pot' bypass capacitors several of which had shorted and rebuilding the BFO circuit.  The inductor for the BFO had been removed; a new inductor was wound on a toroid core and appropriate capacitors were added to resonate the Meissner oscillator circuit at the 2.8 MHz IF.  However, the restoration work came to a halt when it was discovered that the three front end coils for the antenna, RF amplifier and local oscillator tuned curcuits had been completely changed.  At this point the radio sat on the shelf for a few years. 

Last summer he found an old CQ magazine article that described the construction of three front end coils and decided to rewind them per the article (almost).  Four of the five windings were straight, linear ones but the fifth was meant to be universal wound.  A decision was made to try a scramble wound coil with the same number of turns.  The three coils were wound on the original coil forms and replaced into the radio.  The initial testing showed that the local oscillator was operating, albeit at slightly too high a frequency, but that there was a problem in the antenna or RF amplifier stage.

Following the meeting additional work found a bad connection to the antenna coil and now the BC-455 is working.  The tuning range is still too large but the dial calibration between 7 and 8 MHz is now quite close.  Correcting the tuning range would entail reducing the LO inductor and increasing the capacitance in parallel with the variable tuning capacitor.  To attempt this change might be inviting Murphy to pay a visit to the ham shack.  For now WA1TAC is willing to claim success and move on to the next project.

Video recorded by Jim Wilbur, AB1WQ and edited by James Hein, N8VIM