TRF's Where popular during the 1920 RCA held the paten on the Superhetrodyns ,so most manufature had to build the TRF, there where tuned in stages , I restore a Atwater Kent model 20 three dialer you tuned each stage and also ran the voltage on the RF tube filaments and with another reostat you controled the Amp tube filaments my Transitone the volume is controled by running up the RF filaments, I also have some early regenitive sets they are a real blast run the one tube is used as a detector and amp it keeps passing the signal trough it, the ocilate while tuning and make other radios around ocilate along with it ,BILL
