A Four-Tube TRF Receiver
The Get-Started-in-Radio Series
This radio is the sixth and last in our "Getting Started for $8.95" series. The set is a four-tube, tuned-radio-frequency receiver with an untuned stage of radio-frequency coupled to a tuned detector stage with regeneration. Only one coil and one tuning condenser are required, instead of a ganged condenser and a matched pair of antenna and radio frequency coils. The antenna coil has been replaced by a 200,000 ohm, 1/2-watt resistor between the grid and the 25B8GT (pentode section) and the chassis.
The radio frequency portion of the set remains the same as in the previous article, except that an audio stage is resistance-coupled. Bias for the pentode portion of the 70L7GT tube is obtained by means of the 600-ohm resistor and 10-mfd. electrolytic condenser.
The antenna should be from 20' to 100' long. No ground should be used unless it is attached to the chassis through a .1-mfd, 600-volt condenser.