This very dirty behemoth is the RCA designed and built RBA VLF receiver, and is awaiting restoration. This receiver is extremely well shielded, and is a TRF design with a twist. 2 RF amplifier stages, the second of which is operated at very low plate and screen voltage so that it acts as a limiter, followed by a regenerative detector which has a separate oscillator, then another fairly complex limiter stage, and two stages of audio amplification with extensive audio filtering. The audio output stage is configured such that one can connect from one pair to 32 pair of headphones (why on earth would you do that?) with no change in output amplitude. It looks a lot like the companion RBB and RBC receivers, and can use their same power supply. This hulking receiver weighs over 90 lbs and is considered the very best of the TRF designs.