General Electric (G-E) Model J-72 Cathedral Radio (1932)
The General-Electric model J-72 radio was introduced in the fall
of 1932 in time for the 1933 model season. It had a purchase
price of $47.50 complete with tubes. It was manufactured for
G-E by RCA under an agreement made between the companies
earlier that year - see my Westinghouse WR-30 page for more
details. As a result, the chassis was also used by RCA (for
example, see model R-70).
G-E advertised this radio as "a 7 tube early English type compact
with cathedral window type design. Super-heterodyne, full volume, new
type tubes, pentode output, full-size dynamic speaker, and all other
new General Electric features. An unusual radio at an unusually low
It was also described as having "a tone control of the continuous
type". Although this might sound superior even to the four point
controls offered at the time by several other manufacturers,
including Philco, G-E's control was basically a variable HF-cut
type in contrast to the more flexible tailoring of the frequency
response provided by some of the other switchable controls.
The radio covers the American standard broadcast band from
525 - 1550kc and uses an ac-powered 7 tube superheterodyne
chassis. The tube line-up is:- 58 (RF amp), 58 (mixer), 56 (LO),
58 (IF amp), 56 (detector), 47 (power amp), 80 (rectifier).
Compared with its bigger brother the 8-tube J-82, this model
provides no Automatic-Volume-Control (AVC), since it omits the
single-tube AVC stage. Furthermore, it has an unusual
arrangement for manual adjustment of volume in that the control
knob varies the negative bias applied to the type 58 variable-mu
pentodes in the rf, mixer and IF stages. The schematic can be
found at the Nostalgia Air site under the RCA model R-70.
The chassis view of the J-72 to the right here shows the tube
shields and loudspeaker frame painted in red. This is an entirely
original feature, as the several examples of this model that I
have encountered all appear this way. I can only imagine that
this was done for its showroom "wow" effect.
I have restored this radio both cosmetically and electrically. The
chassis is deep and cramped, rendering access to a number of
the old capacitors and resistors difficult. Furthermore, it
originally used a lot of wiring covered with rubber insulation that
had become brittle. All this had to be replaced.
The filter-condensers are housed in a heavy gauge steel can,
affixed to the chassis using lugs, accessible beneath the
chassis but concealed below the mixer/LO coil assembly. This
housing can be seen at the front right of the chassis (viewed
from the rear) in the photo to the right. The coils had to be
removed and the lugs cut off using a Dremel tool in order to
release the unit. Once removed, I dug out the tar and
embedded components with the aid of a heat gun and replaced
them with modern equivalents. The completed capacitor pack
and lugs were then re-attached to the chassis using cement.
..early English type compact with cathedral window design.
Believe your own ears!