regenerative receivers require fewer components than other types of receiver circuit, such as the trf and superheterodyne. the circuit's advantage was that it got much more amplification (gain) out of the expensive vacuum tubes, thus reducing the number of tubes required and therefore the cost of a receiver. early vacuum tubes had low gain and tended to oscillate at radio frequencies (rf). trf receivers often required 5 or 6 tubes; each stage requiring tuning and neutralization, making the receiver cumbersome, power hungry, and hard to adjust. a regenerative receiver, by contrast, could often provide adequate reception with the use of only one tube. in the 1930s the regenerative receiver was replaced by the superheterodyne circuit in commercial receivers due to the superheterodyne's superior performance and the falling cost of tubes. since the advent of the transistor in 1946, the low cost of active devices has removed most of the advantage of the circuit. however, in recent years the regenerative circuit has seen a modest comeback in receivers for low cost digital radio applications such as garage door openers, keyless locks, rfid readers and some cell phone receivers.