Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
These
schematics, tuning instructions, and other data are reproduced from my collection of vintage radio and
electronics magazines. This particular Radio Service Data Sheet is for the Radiola "28," which is a
very unique-looking radio set in the fashion of a small writing desk. As back in the era, similar schematic
and service info was available for purchase from sources such as
SAMS Photofacts, but these printings were
a no-cost bonus for readers. There are 187 Radio Service Data Sheets as of May 2, 2017.
Radiola "28" Super and "104" Power Speaker Radio Service Data Sheet
Condenser C1, in the principal diagram below, is the loop-tuning
condenser, in the input circuit to the first R.F. tube (V1); this may be balanced by an experienced
Service Man, in accordance with standard practice for super-heterodyne circuits, to match the constants
of the loop antenna, by the compensating con-denser C4 (at the left of the loop socket, looking from
the front). Condenser C2 tunes the input to the first detector, V2 (the numerical sequence of the tubes,
when plugged into the catacomb sockets, is: V2, V4, V1, V5, V3, V6, V7, V8, as indicated by the numbers
immediately beneath these in the diagram, which correspond to the numerals stamped in the bakelite top
plate. Condensers C1 and C2 are ganged, and are under the control of the left tuning drum; condenser
C3, tuning the circuit of oscillator V3, is adjustable by means of the right drum. The first R. F. stage
is neutralized by means of condenser C5 and the center-tapped loop; this condenser is mounted on the
bakelite strip carrying the main terminal lugs. The primary of the first I.F. transformer is tuned to
the intermediate frequency (40 kc.) by means of condenser C6; this I. F. circuit is neutralized by condenser
C7 (inaccessible). The dotted rectangle denotes the shield can of the catacomb; everything inside this
line, except the filament connectors. is under seal (to break which cancels all factory repair obligations).
The remaining condensers inside the catacomb are also inaccessible; so is the grid leak, R3.
Posted May 2, 2017
Radio Service Data Sheets
These schematics, tuning instructions, and other data are reproduced from my
collection of vintage radio and electronics magazines. As back in the era, similar
schematic and service info was available for purchase from sources such as
SAMS Photofacts, but these printings
were a no-cost bonus for readers. There are 227 Radio Service Data Sheets as of
December 28, 2020.
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while typing up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
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