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MECA Electronics

Radio Data Sheet Zenith Radio Models 8H032, 8H033, 8H050, 8H052, 8H061
January 1947 Radio-Craft

January 1947 Radio-Craft

January 1947 Radio Craft Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

Zenith 8H032 (Radio Museum) - RF CafeHere is the Radio Data Sheet for Zenith radio models 8H032, 8H033, 8H050, 8H052, 8H061 as published in a 1947 issue of Radio-Craft magazine. Some of the electronics magazines used to include this type of high level documentation so that hobbyists and even service shops with budgets too small to afford cabinets full of SAMS data packets could work on the radios. Most of the radio manufacturers would not even sell factory-prepared documentation to anyone who was not an "authorized" service center. The RadioMuseum website has nice examples of restored vesions of both the Zenith 8H032 and the Zenith 8H034 tabletop radios, as well as an 8H061 floor console model. The electronics are similar but the chassis designs are completely different. They sport three bands: the 540-1620 kHz AM band, the pre-WWII 42-48.5 MHz FM band, and the current 88-108 MHz FM band. A contributor on one of the Antique Radios forums says the 8H034 was nicknamed "The Major," in honor of Major Edwin H. Armstrong. As of the writing, the Antique Radio Schematics (note the misspelled "Antoque" on the homepage.) claims to sell copies of original factory service manual for thousands of vintage radio, record players, and televisions.

Radio Data Sheet Zenith Radio Models 8H032, 8H033, 8H050, 8H052, 8H061

Radio Data Sheet Zenith Radio Models 8H033 - RF CafeRadio Data Sheet Zenith Radio Models 8H032 - RF CafeFM-AM A.C. Superheterodynes

Tube Complement: 6AG5 r.f. amp; 6SB7 converter; 6SG7 1st i.f. amp; 6SH7 2nd i.f. amp; 6SH7 limiter; 6S8-GT discriminator-detector and 1st a.f.; 6K6-GT power output; 5Y3-GT /G rectifier.

Power Rating: 0.645 amp at 117 volts

Tuning Range: AM 540-1620 kc; FM 42-48.5 mc; 88-108 mc.

Alignment Procedure

The 8C20 chassis incorporates a superheterodyne circuit with two stages of i.f., and one stage of r.f. amplification on all bands.

AM Alignment

The alignment of this chassis on the standard broadcast band is conventional. The alignment slugs in the i.f. transformers are threaded and screw into the coil forms. The slugs are slotted for a small size fiber screw driver. Do not press hard on the aligning tool (fiber screw driver) or the threads in the coil forms will strip and adjustment will be impossible.

FM R.F. Alignment

The same coil slug arrangement which tunes the 100 mc FM band also tunes the 45 mc band. However, on 45 mc the band switch connects trimmer condensers in parallel and padding wires in series with the 100 mc coils. The tuning slugs are attached to threaded shafts and the slugs are varied in the field of the coils by turning the shafts clockwise or counter-clockwise. After adjustments the shafts must be secured with a drop of speaker cement. This will prevent changes due to vibration or tampering.

FM I.F. Alignment

The same type of tuning slugs for aligning the AM .i.f. amplifier are used far the FM i.f.'s. Observe the same precautions when making adjustments. The second 8.3 mc i.f. stage is over-coupled. Over-coupling gives a wide band pass with good sensitivity. When an over-coupled stage is aligned with an unmodulated signal, the stage must be loaded. A 300-ohm carbon resistor soldered across the secondary of the second i.f. transformer provides a satisfactory load for this circuit. The resistor leads must be kept short to reduce the distributed capacity of the circuit.

When aligning a loaded stage, it will be found that considerable signal from the generator will be required, and that it will tune broadly. The load resistor must be removed after alignment.

If the signal generator used does not have sufficient output to overcome the temporary loss caused by the load resistor, the load resistance may be increased or the signal fed into the preceding stage.

FM Discriminator Alignment

When the secondary of the discriminator is aligned (operation 6) use sufficient signal input to get a good positive and negative indication before setting the slug for zero reading. A center zero indicating meter is recommended for this adjustment, but is not absolutely necessary. Reversing the leads of a non-zero center meter, or observing closely when this meter starts to go to the left (negative) of zero will give the same results.

Alignment of FM receivers is a special job and calls for knowledge of their characteristics. Articles on FM servicing were printed in Radio-Craft, March 1946 and March 1944.

Important: Alignment of this chassis will in most cases be unnecessary unless an i.f. or r.f. transformer is replaced or the adjustments have been tampered with.

Correct alignment can only be made if the following procedure is followed:

A vacuum-tube voltmeter with an isolation resistor of 200,000 ohms in series with the hot lead will serve for FM adjustments. This lead should be shielded.

An a.c. output meter connected across the primary or secondary of the output transformer will be satisfactory for all AM adjustments. The signal generator output should be kept just high enough to get an indication on the meter.

(a) Vacuum tube voltmeter pin 5 on discriminator transformer to chassis (half discriminator load).

(b) Vacuum tube voltmeter pin 7 on discriminator transformer to chassis (full discriminator load).

(c) Vacuum tube voltmeter 6SH7 limiter grid (pin 4) to chassis.

(d) 300-ohm 1/2-watt carbon resistor soldered across the secondary L17 (pin 2 and 3 of 2nd, i.f. trans.). The leads to the resistor must be as short as possible and the resistor removed before operation 10 is started.

 

 

Posted July 16, 2020

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 222 Radio Service Data Sheets as of July 10, 2019.

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