BC-348 RESTORATION
May 2007 -
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May, 2007: Introducing the BC-348
Communications for long-range WWII aircraft; comparison with command sets; basic features; controls; evolution; differences between models; physical and electronic design.
June, 2007: More on the Trans-Oceanic and BC-348
(See Trans-Oceanic section for T-O content)
Identification of our 348 model; assessment of cosmetic condition; speculation re. the Pan American Airways asset tag.
July, 2007: BC-348 Restoration Begins
Removal of access plates; removal of front panel; cosmetic panel restoration; identifying previous owner‘s power supply connections.
August, 2007: Recapping the BC-348
Need for wholesale replacement of all those paper caps that look like micas; carrying out a general replacement strategy; on line sources for manuals.
September, 2007: The BC-348 Restoration Continues
In-circuit resistor checking; finishing front-panel cosmetic restoration; re-installation of panel; installing connecting wiring for power supply.
October, 2007: The BC-348 Gets a Smoke Test
Cleaning and touching up the knobs; applying plate and filament voltages from temporary supplies; no smoke but no signals; removing and cleaning the dual volume control; diagnosis to await construction of permanent power supply; considerations for hooking up a speaker.
November, 2007: Power Supplies For the BC-348
Acquiring a power supply transformer and choke; preparing a Masonite base, or "chassis" to fit over dynamotor well; the power supply circuit; controlling the too-high plate voltage; reader circuit for a solid state dynamotor replacement.
December, 2007: A Permanent Power Supply For the BC-348
The PAA asset tag explained; relocating B plus dropping resistor to control hum; converting to a choke-input filter to drop the resulting too-high B plus; routing a.c. power through the original interface plug using slip-on connectors; bypassing the original "on-off" switch; connecting up the power supply.
January. 2008: The BC-348 Begins to Talk
B plus fuse installed; output transformer and speaker installed; dead i.f. stage pin-pointed and corrected after location of mysterious intermittent short; Signs of life appear.
February, 2008: The BC-348 Awakens--Sort Of
First real signals received, but sensitivity is low and audio intermittent and fuzzy; B plus voltage readjusted; leaky audio coupling capacitor located; realignment planned.
March, 2008: Aligning the BC-348
Leaky audio capacitor replaced, along with a tone-control capacitor found missing; audio now reasonably clean; B plus voltage corrected again--possibly a result of changes in current drain caused by repair of audio stage; i.f. channel alignment still mostly spot on, only minor corrections needed; front end adjustments require more correction--especially in 1.5-3.5 MHz band; LM freq meter used to verify oscillator frequency on this band; sensitivity now improved, but r.f. stages found to provide no amplification.
April, 2008: Finishing Touches For the BC-348
Readers‘ BC-348 Adventures; weak r.f. stage corrected; voltage regulator lamp problem possibly traced to intermittent oscillator operation.