BC-224-A radio receiver
Trust me, I really did try my very best not to build this bay, but then I suppose one could say that about any of the bays in the "flight deck". However, a slow, extremely erratic accretion of oddball but technologically important mid-1930s pieces has finally forced me to do something with them. A bit more room created in a move from basement to outbuilding helped the prospects enough to make me start thinking in a more positive way about the work involved. The result is showing up here, though it is under construction and it will be some time before final locations of equipment on each shelf are determined (through a very scientific approach called "try it there for a while and see how it works").
Until then, here is a sneak peek, at least of the principal rigs going into this bay. Like everything in this hobby, there is no Gantt chart for progress nor target for completion, just a vague hope that it will occur sometime out there in the future "before too long". Nothing has been restored at the moment, so what you see is what it looks like going into this adventure. As progress is made, I'll replace the pretty sad looking place-holder photos with finished appearance.
The mid to late 1930s reflected a curious mixture of old and new thinking in aircraft radios, led by brilliant engineers in such companies as Aircraft Radio Corporation and RCA. The example below should endear itself to every radio amateur growing up in the 1940s or 1950s, because it was the first of the BC-348 series of aircraft receivers. A close look at its front panel will reveal the same controls that are on all the later BC-224/348s, with the addition of a "heater" switch and some relocation from the more familiar positions. (The BC-348-J, N, and Q also deleted the antenna alignment, of course.) This innovative receiver has a circuit diagram that looks very similar to its later counterparts, as well. There was a curious inclusion of a short transmission line between the left and right side of the receiver along the bottom edge of the front panel, presumably to make antenna connections easier on some aircraft installations. The familiar eight pin Jones style power plug was identical to the later models, and though the FT-154 shock mount did not have the same depth as the later FT-154-*, it appears identical to the casual glance.
The similarity to the later radios is striking. The use of basically the same knobs that were used on thousands of its progeny cements the relationship.
This particular example was unmolested in the post-war rush by many radio amateurs to personalize their military sets, which produced every shade of paint and modification under the sun. I have another example of a BC-224-A (what I would have to charitably call a parts set) in which someone had mounted miniature tubes and replaced the front panel with a carefully machined 19" rack panel! The pristine one going into the bay now has an original dynamotor from a good friend that was more akin to the BC-312/342 approach, being mounted in a stainless steel box that occupied almost 1/8 of the receiver cabinet volume.
The traditional post-1935 transmitter match for this receiver was the BC-AA-191, detailed more fully
here.
There is a switch in the BC-AA-191 that allows selection of two different series receivers, one of which is the
BC-189 shown below. The main reason for this switch is to coordinate the antenna relay with receiver blanking
when sending CW.
In the new 1930's bay, this switch will allow antenna relay coordination with either of these
receivers (Position No. 2 works well for the BC-224-A). For those interested, there is a 1932 IRE Journal article on
the BC-AA-191's predecessor located
here.
The BC-189 is not as capable a receiver as the BC-224-A. Bandswitching was accomplished by replacing the tuning coil drawer, for example, and interpolation charts were required to understand what frequency the receiver was tuned to, but it weighed less and was simpler to operate for non-technical airmen.
GE also produced a smaller transmitter for aircraft use that was sort of in-between the liason and command set in power output, called the BC-307. With the BC-224-A, the combination was labeled the SCR-238. The transmitter is shown below. This particular unit is a BC-307-A - the date on the tag is 9/12/1936 - though they were manufactured in a -B model up through 1942. The scale may be misleading to those who are familiar with the BC-375 sized transmitters - this cute little thing is only 14" tall!
The frequency tuning charts were made out of .038" aluminum, with black silk screened lettering on them. On top of this transmitter can be seen one of the blank charts that have been reproduced on the mill prior to silk screening. Actually, this particular example is not as bad as it looks in this photo. The external panels will need to be repainted (unfortunately), which means all the engraving will have to be done again, but internally it is in fairly nice shape.
The bay wouldn't be complete without some representation of the lower power "command" sets - as opposed to the greater capability "liaison" set described above. In the USAAC, that role was served by the SCR-183, dating back to the early 1930s. An example of that set is shown below, this one an "AE" variation from 1935. There was a similar set designed and produced for the US Navy (called the RU/GF series), but it had some diverging differences in circuit design and tube types as the years rolled on.
Okay, I know that the set below isn't 1930's vintage, but I couldn't figure out a decent place to put it, other than this bay. It represents probably one of the best known of all the "command sets" simply because so many folks saw and bought them after the war. It has a lot of similarities to the AN/ARC-5 set, but there are subtle differences - the lack of a fully functional AVC in the receivers being just one of them. The original plan for this set involved a roll-around rack to take to hamfests just to stimulate conversation and for others to enjoy, but there has been a reduction in the number and size of this grand tradition, and my QTH relocation has diminished the availability and convenience of getting to the larger hamfests, so here we are.
This is the entire SCR-274N set, with a couple of uncommon four unit racks and shock trays. It will look more organized when everything is mounted in the bay. Receivers were typically mounted underneath a radio operator's table, transmitters above where he could see them, mostly because the receivers have remote control boxes that have slave frequency indication dials and gain controls on them.