This Bang & Olufsen table-top receiver dates from the early 1950s. This particular unit made its way to Canada recently, it was not a period import. Consequently the labelling is in Danish, and while the design provides for operation at various voltages it was configured for 220VAC.
This model has a longwave, broadcast and two shortwave bands:
As with many European radios from the period the dial is scaled by wavelength rather than frequency, and the dial is quite large to accommodate the names of stations from many cities around Europe.
The 4 controls, left to right, are:
The tone control on European radios is often rather complex, at least in comparison to the typical simple capacitor-and-variable-resistor implementation of North American radios. In this model the tone control is a 7-position, 7-pole rotary switch. Internally, the poles control 7 different circuits in the receiver: two for IF selectivity, the negative feedback in the audio amp, and several other audio filter points. Functionally, the 7 positions are divided into 3 groups: voice, normal and bass-boost, with the additional positions providing some treble variation within each group. While there are limitations to 7 discrete settings, the control is nonetheless quite effective.
The tube line-up is UCH21 (mixer and oscillator), UBF80 (IF amp, detector), UAF42 (1st audio), UL41 (audio output). While there are just 4 active signal stages, performance is good in terms of both station sensitivity and audio power and quality.
The power rectifier is a dual selenium unit. For 220/240V operation this is configured for simple half-wave rectification. Voltage selection options allow it to be configured as a voltage doubler for 110-125 VAC operation.
A gramophone input is provided, with a position on the band switch to select it, however the input does not feed into the 1st audio amp. Instead, the IF amp is leveraged as a phono amplifier with some switch-selection. While a novel bit of circuit design, this adds significantly to the complexity of the receiver, necessitating 3 additional poles on the BAND switch.
Schematic available upon request.
Aside from the repairs necessitated by this damage and other general repairs, most of the work involved redoing some earlier repairs to the power supply and configuring the unit for 115VAC operation.
Repair summary (2011 Jun):
Bang & Olufsen Jet 508K