Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
In a continuing effort to provide archival material for researchers
and for anyone seeking information on a particular radio restoration
project, this Radio Service Data Sheet for the Zenith Model 430/440
radio from a 1933 edition of Radio-Craft is being posted. An Internet
search will show that there are many people engaging in such activities.
Restoring my
Crosley Model 03BC console radio would have been more difficult
if not for others who have done similar work to
assist the 'community.'
I generally despise the phrase "giving back" because it is usually
uttered by people that really owe nothing to anyone, but somehow
feel obligated to do so or are conditioned to automatically say
such things. This is a case where I benefitted from somebody else's
work and there is an opportunity to return the favor.
Update: Mr. Steve of The Radio Fox website wrote to express thanks for having this information
posted. He owns both a
Zenith Model 430 and a Zenith Model 440(click thumbnails).
Zenith Models 430 and 440 12-Tube Superheterodyne Radio Service
Data Sheet
(Dual
reproducers, Zenith class AAA A.F. power amplifier; illuminated
auto type full-vision control escutcheons; 540 to 1750 kc. - 121
channels, including police band; silent tuning; A.V.C.; low-volume
tone compensator; "shadowgraph" tuning; tone control; 110 V. or
220 V. line.)
The newest product of Zenith Radio Corp. is the model 430 receiver;
equipped with the Zenith automatic tuning device, it is the model
440. The outstanding feature of this set is the "class AAA" system
of A.F. amplification used;
Line potential, 115 V.; all controls maximum.
All tube readings, except heaters, are socket to ground, using
1,000-ohms-per-volt D. C. meter.
Condensers C1, C2, C3, tuning gang; C1A, C2A, C3A, tuning trimmers;
C4 to C7, I. F. trimmers; C8, L. F. padder; C9, H. F. coupling condenser;
C10, C11, C12, 0.2-mf.; C13, 0.1-mf.; C14, C15, C16, C17, C19, C20,
C24 (25 cycles, 0.4-mf.), C30, C31, C35, .1-mf.; C18, 0.05-mf.;
C21, C22, C23, C25, C26, C27, 8 mf.; C28, 0.5-mf.; C29, 25 mmf.;
C32, C33, 500 mmf.; C34, 0.002-mf.
The condenser gang in this receiver is aligned at 1,500 kc.;
the oscillator padder is aligned at 600 kc.
Field coil No. 1 has a resistance of 1,600 ohms; field coil No.
2 has a resistance of 2,000 ohms for section A and 3,500 ohms for
section B. Choke Ch.2 has a resistance of 400 ohms.
There are no circuit changes or switches in this receiver for
the reception of police calls. The tuning dial, itself, actually
takes in the police frequencies since it covers a total range of
540 to 1,750 kc.
"Shadowgraph" tuning is effected by means of a vane fastened
to a meter movement connected in the plate-supply circuit to tubes
V1, V2, V3. The incoming signal causes this "meter" to move in the
usual manner, thus twisting the vane so that it either obstructs
the light and casts a wide shadow (off resonance), or permits the
light to pass, casting a shadow no wider than the thickness of the
vane (exact resonance of the tuned circuits).
Class AAA A.F. amplifier is the Zenith designation for a system
employing three power tubes, each of which are biased as class A
amplifiers, one of which is used to drive the other two in push-pull.
If the grids were overdriven with the usual type of coupling transformer,
having a high secondary impedance, between the driver and the output
tubes and the push-pull grids overdriven, extreme distortion would
take place. This difficulty is overcome by employing a special transformer
of step-down ratio having larger wire and much less resistance in
its secondary. This transformer is a very important part of the
system. With such an arrangement it is possible to drive the grids
of the power tubes positive without introducing distortion, because
of the driver being a power tube and capable of supplying the necessary
current on such peaks. The primary of this transformer has a higher
impedance than is normally used, which value is somewhat reduced
as the impedance changes in the secondary, when the power grids
are driven positive. Its impedance, however, at the lowest value,
still matches the driver plate circuit. It should be remembered
that in an ordinary class A amplifier distortion enters when the
grids are driven positive by virtue of the previous tube not supplying
sufficient power for grid excitation of the output tubes. In other
words, in class A, voltage on the power grids is available as long
as they do not go positive. As soon as they are driven past zero
in that direction the previous amplifier can no longer supply the
necessary power.
Above, Arrangement of the tubes in the "430." Right, Comparative
figures indicating the effectiveness of A.F. amplifiers classes
A, push-pull; B, push-push; pentodes in push-pull, and AAA, push-pull,
Watts rating, respectively, 4.3 W., 0.8- to 24 W., 6.3 W., 14.2
W.
Summing up the above, the triple A amplifier is a combination
of both class A and class B. The exception being that the tubes
are biased as class A, but by virtue of the power delivered by the
driver and the special coupling transformer, sufficient power is
supplied for the power tube to draw grid current and still prevent
distortion as in the class B amplifier.
Many set analyzers will not accommodate the new tubes, consequently,
all voltage readings are to ground. Thus, for instance. the actual
voltage on the plates of the power tubes is 295 V.
The two reproducers are similar in construction but one is peaked
at 90 cycles and the other at 70 cycles. (This is done to cancel
the natural period of each reproducer.) The paralleled voice coils
result in four times the power obtainable from a single reproducer,
states the manufacturer.
An overall sensitivity of less than one-half microvolt-per-meter
is obtained with an undistorted power output of 15 watts. The total
line consumption at 115 V. is 125 W.
Posted March 24, 2015
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
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