Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
QST, published December 1915 - present (visit ARRL
for info). All copyrights hereby acknowledged.
The expectation of manufacturers to constantly
come up with new and better models that outperform last years' models and compel
buyers to upgrade is as old as markets themselves. This tongue-in-cheek tale of
developers of the "The Dual-Ratio Knee-Action Triple-Hemispheric Multi-Tube Many-Wave
Looperdyne" could easily be adopted to describe the prototype lab at Apple, Chevrolet,
Panasonic, Microsoft (well, maybe not so much), Hasbro,
Lockheed Martin, or Craftsman. Anyone who has worked in the pressure cooker environment
of a research, development, and production qualification phases of a project knows
all too well the scenario presented here.
Behind the Scenes with Next Year's Model
The Tale of a New Receiver's Evolution
By J. N. A. Hawkins, W6AAR
The recent trend toward all-wave broadcast receivers has aroused much interest
among amateurs and others, and many have expressed an interest in how the new developments
happened to see the light of day. The principles of design are considered quite
mysterious and deeply scientific; so we conducted an investigation among the engineering
staffs of receiver manufacturers in order to get the story behind the development
of a new model.
Herewith we present the highlights in the development of a typical receiver,
"The Dual-Ratio Knee-Action Triple-Hemispheric Multi-Tube Many-Wave Looperdyne."
President tells Chief Engineer that sales are dropping off on current model so
a new one is necessary. As the Chief Draftsman is on his vacation, the Chief Engineer
gloomily reflects that he will have to use a new man and have to do all his own
calculating. Sends to Purchasing Agent a requisition for a copy of the Handbook
and a 10-inch slide rule.
President sends memo that compactness and portability are the watchwords. Chief
Engineer outlines three-tube design to draftsman, with radical new chassis design
and spherical bakelite cabinet. Special dies purchased at cost of $1,972.34. Sales
Manager points out that he forgot the loud speaker. Dies scrapped. Memo from President:
Short-wave reception is the coming thing, and compact sets are on the way out. Chief
Engineer makes requisition for subscription to QST, another Handbook and a 16-inch
slide rule. Lays out new chassis and designs tuning condensers and coils for 3-to-1
frequency ratio in each band. Draftsman can't read his writing, so provides only
a 3-to-1 gear reduction in the tuning dial. Bad intercoupling between various tuning
ranges causes continuous dead spots; coil and switching assembly redesigned and
shielded. Draftsman points out that new coil assembly won't fit on chassis. Chief
Engineer eliminates power transformer and sends memo to President pointing out advantages
of new 25Z5 transformerless power supply and full a.c.-d.c. operation. Memo from
President points out that 25Z5 rectifier is out, as there are 6,920 type 80 rectifiers
still in stock room and must be used up. Chief Engineer lays out new chassis 4 inches
Memo from Sales Manager that RCA is planning new Class-C audio amplifier. Chief
Engineer scraps audio channel for Class-C type. RCA designer scraps his layouts
of Class-C audio amplifier and plans new Class-D-Prime audio amplifier, after hearing
that Philco plans to use it. Philco designer scraps Class-D Prime because it takes
10 watts of driver power to get 7 watts of output to the speaker, and adopts new
Majestic "Cold Control."
Cabinets for the new model arrive from Furniture Manufacturer. Chief Engineer
suddenly remembers he forgot to notify Furniture Manufacturer that 4 inches were
added to the width of the chassis. Chief Engineer eliminates one i.f. stage, the
tuned r.f. stage ahead of the first detector, 8 mikes of filter condenser and washes
out the audio transformers in favor of resistance coupling. By mounting 16 resistors
and 5 bypass condensers in the half-inch gap between the three-gang condenser and
the chassis he manages to squeeze the new layout into the new cabinet. Service Manager
points out that power transformer, three-gang condenser and the filter condensers
must be removed to test or replace the 16 resistors or the 5 bypass condensers.
Chief Engineer buys his silence with case of "Old Crow" and a promise to adopt Crosley
Shelvador on future models.
President returns from I.R.E. Convention and announces that High Fidelity is
the watchword - sensitivity and selectivity must be compromised to obtain it. Design
is altered to suit. Class-C audio channel is scrapped for a pair of 845's in Class-A.
Shop error makes i.f. shield can five inches in diameter instead of two-and-a-half.
In exchange for past favors in covering up his errors, Chief Engineer writes long
memo to President pointing out that large shield can raises Q in i.f. transformers
and increases gain so that one i.f. stage can be eliminated. President skips involved
calculations about large shield cans, tells Shop to eliminate one i.f. stage and
add a beat-frequency oscillator for help in finding short-wave stations; also to
add an inter-station noise suppressor, as Majestic is reported to have one in their
new model. Chief Engineer and Shop Superintendent go into conference and decide
that the beat oscillator and the noise suppressor had better be mounted inside of
the five-inch i.f. can, and say nothing more about it.
Power transformers arrive from manufacturer
with terminals on the side instead of the bottom. After long correspondence with
Transformer Manufacturer, Chief Engineer decides to keep mum about it and just mount
the transformer underneath the chassis in place of the three-gang condenser, which
he mounts on a bracket hung from the loud speaker. Power pack delivers only 200
volts. Transformer Manufacturer points out that Chief Engineer's specifications
called for a 400-volt secondary instead of an 800-volt secondary center-tapped,
which would be necessary to get 400 volts of output with a full-wave rectifier.
After three sleepless nights trying to get the experimental model to operate on
the 200 volts supplied by the new power transformer, the Chief Engineer gets the
Office Boy (who is a ham in his spare time) to draw him a bridge rectifier circuit.
Sends long memo to President suggesting use of two 25Z5's as bridge rectifier.
President is somewhat hazy on the Chief Engineer's involved vector diagrams and,
as he has also forgotten about the 6,920 type 80 rectifiers still in stock, he OK's
the change and tells the Chief Engineer to make it a long-wave receiver for the
export business, which is picking up. Chief Engineer sadly adds another set of r.f,
and oscillator coils to cover the range from 400 to 150 kc. and thus is forced to
change the intermediate frequency from 260 kc. to 465 kc. Receives memo from Purchasing
Agent asking whyinhexx he changed the intermediate frequency the day after a shipment
of five thousand 260-kc. i.f. transformers arrived from the Coil Manufacturer.
First production models show extreme instability and go into oscillation on the
least provocation. Since the Foreman of the Sheet Metal Shop does not speak English,
the Chief Engineer waves his arms around to show the shape of the new shielding
baffle that he wants to put between the i.f. and the first-detector tubes. Misunderstanding
him, the Foreman turns out a startling new triple-deck chassis, and orders $3150
worth of dies to make it. The Chief Engineer has a drawing made of the new idea
and sends it up to the President, pointing out that his new development will probably
triple the sensitivity of the set due to the improved shielding.
High pressure Salesman sells the Purchasing
Agent a new type of loud speaker. All is well until it is found that the chassis
is 3/4 of an inch too high to allow the speaker and chassis to inhabit the same
cabinet at the same time. Chief Engineer saws the bottom out of the cabinet and
mounts the chassis 3/4 of an inch lower. The holes in the front of the cabinet for
the tuning, volume and switch controls being now out of line with the control shafts,
Chief Engineer finds it necessary to mount the chassis upside down in the cabinet.
Sends memo to the President pointing out that new chassis position and bottomless
cabinet allow the set to be adjusted and lined up without taking the chassis out
of the cabinet. President sends back memo asking how the i.f. tube and the second-detector
tube are removed without removing both the chassis and speaker from the cabinet?
C. E. makes front of cabinet removable in order to get at tubes.
Assistant Sales Manager writes letter from field to President asking why dealer
delivery promised two months ago is not yet being made, and pointing out bitterly
that delivery of new lines by three competitors in his territory has already curtailed
future orders by 50%. President sends mandatory order to Production Manager to put
out new models without further delay and instructs Sales Manager to lower retail
price by $5 and cut dealer discounts in order to compensate for competition. Sales
Manager resignedly junks $6100 worth of printed literature in connection with big
dealer display program on new model in order to feature new price and so informs
President. President figures rapidly that 34% more units must now be sold to make
up total investment on the new model, but since this represents an increase of only
120% over their net production of last year does not feel too discouraged and prepares
to leave on fishing trip to Canada just as Service Manager discovers that last two
changes made in assembly by Engineering Department were unreported to him, with
result that all servicing literature and instructions must be recalled and new material
As President is boarding train, telegram is handed him from Vice-President in
attendance at RMA Convention, where it has been decided that in interests of stabilization
of the industry no new home models be introduced during balance of year, but instead
that vigorous campaign be launched to popularize automobile radio.
President goes fishing. Chief Engineer goes nuts .
Posted August 23, 2022
(updated from original post