Steve -I see you are in Iowa City (many memories 83-95), met Jim Van Allen in 83 when in grad school. Last saw him in 1999, when I was on campus.
Look like this RBA-5 example ?http://www.virhistory.com/navy/rcvrs/ww2/rbb/rba5-01.JPG
Check page 6, USS New Jersey Oct. 2003 newsletter
(An RBA-5 being brought on-board, loan 2003)http://www.ussnewjersey.com/vol2-10.pdf
The new design (RBA series)
was going to blend the advantages of the TRF designs of the RAK but eliminate the regenerative detector in an effort to keep the radiation on the antenna to a low level that prevented enemy DF of the receiver location.
... the new receiver (RBA series)
was not a superheterodyne, the BFO had to track the tuned frequency, providing a 1kc heterodyne which allowed CW to be readily copied. http://www.radioblvd.com/WWII-PostWar%20Hamgear.htm
There were a couple of reasons for not designing the new LF receiver as a superheterodyne.
First was to allow complete coverage of the tuning range of 15kc to 600kc and second was that fact that the conversion process in a superheterodyne creates a lot of internal noise in the receiver - not a real problem on HF or SW, but a serious determent to good LF performance.
At $3000 each, the new RBA receiver was certainly expensive and a look inside the receiver reveals an incredible level of electro-mechanical design and construction. The tuning ranges from 15kc up to 600kc in four bands. The illuminated dial readout is direct in kilocycles along with a two-dial logging scale. The mechanics of the design allow for super-smooth operation of the tuning system. The Gain adjustment controls the sensitivity of the receiver and a gear-driven auxiliary gain control operates from the tuning dial and provides constant gain levels across the tuning range. Two meters are provided, one to monitor Output Level in db and one to monitor the B+ voltage. An Output Limiter is provided for noisy conditions or unexpected strong local signals with the Output Level adjustment setting the output limiter's maximum level. Two levels of selectivity are provided, Broad selectivity is limited to about a 1300kc audio roll-off via an internal LP filter and the Sharp position is provided by a 1kc bandpass filter for CW in noisy conditions or in cases of interference. Audio output is 600 ohms Z and is intended for earphones although the RBA will drive a matched loud speaker if necessary.
The separate power supply, CRV-20130, provides the filament voltage and B+ requirements via an armored cable with heavy-duty connectors. The power supply will easily operate two receivers for emergency conditions and two separate connectors are provided. This is the same power supply used for the RBB and RBC receivers.
The power supply has a cold-cathode regulator tube (OC3) and a HV rectifier (5U4.) The RBA uses eight tubes, three 6SK7 RF amplifiers, one 6J5 Triode Detector, one 6SK7 BFO, two 6SJ7 AF amplifiers and one 6K6 AF Output.