Valve Radio This American portable mains / battery radio is in need of further attention, it has been modified in the past and the connections to enable it to work off batteries have been removed. I did not know the model number so had been unable to locate a schematic diagram. A similar radio has recently been offered for sale on Ebay which appeared to be in better condition. Fortunately the description enabled me to identify it as a model LB-673 and thus to obtain service notes and schematic diagram from www.nostalgiaair.org/
This receiver is intended to work with a LT supply of 9 volts an HT supply of 90 volts or an AC/DC supply of 105-125 volts at 40-60 Hz. It is a single waveband superhet with one RF stage and one IF stage covering the range 540- 1700 Khz. The valve line up is as follows: 1N5GT, 1A7GT, 1N5GT, 1H5GT, 3Q5GT and 35Z5GT
The "beamascope" is a shielded-loop antenna that eliminates the nuisance of outside antenna and ground connections. This antenna also has an added advantage in that it is shielded from the electrostatic component of reception and responds only to the electromagnetic component. Since noise such as static is stronger in the electrostatic component than in the electromagnetic component, this troublesome factor is materially reduced. This elimination is accomplished by rotating the beamascope until the electromagnetic field of the noise source is either eliminated or reduced to a minimum.