September 1934 Radio-Craft[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Radio-Craft was published from 1929 through 1953. All copyrights are hereby acknowledged. See all articles from Radio-Craft.
Here are the schematics, chassis layout, and service info for the Howard Explorer Model W Deluxe 19 Tube All-Wave Superheterodyne radio. The Radio Service Data Sheets that were published in Radio-Craft usually seem to have more information included than those published in other magazines, at least in the same era (1940-ish). It might have to do with how much material is provided by the manufacturer rather than a decision by the magazine editors. Believe it or not, there are still people searching for such data.
(Uses single-purpose tubes to secure extreme circuit stability: wavelength range, 13.6 to 2,142 meters; provides for either inverted-L doublet antenna; neon resonance indicator; zero-beat oscillator; variable Q A.V.C.; tone control; variable A.V.C. parallel push-pull output 245s.)
A 19 tube radio receiver in its home. Airplane-type dials are used; only the tuning dial sector of the band in use is illuminated. as the band switch is turned.
Schematic circuit of the A.F. amplifier and power pack chassis. There are 9 tubes in this section of the instrument. A "theatre" type dynamic speaker is used,
Until very recently the general practice has been to utilize the new tubes at their maximum capabilities. Consequently, a slight change in characteristics would greatly affect the operation of the complete receiver. However, this 19 tube set is designed to utilize its tube complement very conservatively, with the result that great stability has been achieved which, after all, is a major factor in securing satisfactory reception, especially on the short waves.
Note; it is inadvisable to attempt to realign the set except as a last resort. The recommended procedure, only to be used by expert radio Service Men, is as follows:
To align the I.F. circuits feed the I.F. service oscillator test signal into the control-grid of V2.
When aligning R.F., I.F., or oscillator circuits turn A.V.C. adjustment (slotted shaft) to extreme left. The I.F. trimmers are very critical, greatly affect the performance of the set, and must be carefully resonated.
Aligning R.F. and Oscillator Circuits
Adjust A.V.C. control to extreme left position. It is unnecessary to remove the set oscillator tube. Align the circuits only in the sequence given.
To align the set oscillator turn its trimmer all the way out and then select the strongest signal when turning it in; set insensitivity near the center of the dial will result if the wrong oscillator signal is used.
Bend the variable condenser plates for kc. dial alignment only in the broadcast band. Before adjusting any band, make certain that the pointer of the station indicator is set on the last black line when the dial is turned all the way to the left on the broadcast band just above 0.55 (Maximum capacity of the variable condenser).
Turn the band indicator to 0.15-0.35, set the dial to 0.35, and feed 350 kc. into the antenna post. Resonate the trimmer (not green coded on the trimmer washer) in the long-wave oscillator can. Align the R.F. and antenna stages. Reset dial to just above 0.17 and resonate the green coded oscillator trimmer at 175 kc. Recheck the 350 kc. setting.
It is necessary on the broadcast band only, that a metal plate with holes in line with the trimmer nuts be used so that the circuits are not detuned when the regular base plate is screwed back on.
Turn the band indicator to broadcast 0.55 to 1.5, set the dial to 1.4, and feed in 1,400 kc. Resonate trimmer 14, R.F. trimmer 7 and the antenna trimmer (knurled knob extending from top of antenna coil can). Now rotate dial to 0.55 and resonate trimmer 10 at 550 kc. Re-check the setting at 1,400 and bend plates of variable condenser at 950 and other points where necessary to secure kc. reading on dial.
Short-Wave Band No.1
Turn band indicator to 1.5 to 3.5, set dial to 3.5, and feed in 3,500 kc. service oscillator signal. Resonate trimmer 13, R.F. trimmer 6 and antenna trimmer 3. Rotate dial to 0.55 on broadcast hand. (The short-wave dial calibration may be inaccurate at this point and the 0.55 figure corresponds to 1.5 on short-wave band No. 1.) Feed in 1,500 kc. and resonate trimmer 9. Recheck at 3,500 kc.
Short-Wave Band No.2
Turn band indicator to 3.5 to 9, set dial to about 8.9 (due to off-calibration this corresponds to 8.5), and feed in 8,500 kc. Resonate trimmer 12, R.F. trimmer 5 and antenna trimmer 2. Rotate dial to 3.5 and resonate trimmer 8 at 3,500 kc. Recheck at 8.5 (8.9).
Short-Wave Band No.3
Turn band indicator to 9 to 21, set dial to 20, and feed in 20,000 kc. Resonate oscillator trimmer 11, R.F. trimmer 4 and antenna trimmer 1. The alignment at 9 is obtained by use of the fixed condensers which should not require change. To insure band sensitivity in the region of major foreign program reception, turn the dial to 12 and resonate antenna coil trimmer 1 at 12,000 kc.
Note that since all adjustments are made with the A.V.C. inactive, extreme care must be used to attenuate the input signal low enough so that there will be no overloading of tube amplifiers while making adjustments.
After these high-frequency adjustments have been made, the service oscillator setting should be advanced 930 kc. and the output signal strength considerably increased; non-reception of the image signal indicates incorrect set oscillator adjustment. For example: a service oscillator signal of 20,930 kc. should be perceptible at 20 on the dial after alignment to 20,000 kc.
Beat Oscillator Adjustments
Turn the main dial to receive a service oscillator signal of 4,800 kc., and make sure that the band on the "beat oscillator" (Frequency Meter V17) falls on 1.5 when the 2 gang condenser is at full capacity.
Turn Osc. Sw. to the right ("Mod."), and frequency dial to 4. Resonate the trimmer on the 2 gang condenser to main dial setting. Turn band indicator switch to short-wave band No. 1 (1.5 to 3.5), set main dial to where 1,500 kc. comes in, turn frequency dial to 1.5, and then resonate trimmer 15.
Connect one side of a high-resistance voltmeter to A. V.C. potentiometer terminal which connects to the "high" side of the 0.2-meg. resistor and to the 0.1·mf. fixed condenser, and the other (positive) to chassis ground.
Adjust the receiver for reception of a signal intensity of 3,000 to 4,000 micro-volts, and vary for maximum voltmeter reading, in a given locality, the adjustment in the top, next to the neon adjustment, of the coil can assembly in the upper right-hand corner (facing rear of tuner).
In certain localities close to a broadcast station it may be necessary to readjust the A. V.C. (slotted shaft) control. Exactly resonate the receiver. Then, if the station's signals sound "fringy" or rough, turn the control to the right only sufficiently far to correct this condition.
Neon Tuning Indicator and Q.A.V.C.
Facing the back of the tuner chassis, extending through one of the tall shielded assemblies in the upper right-hand corner, will be found a small, black knurled knob used to adjust the neon resonance indicator. It is advantageous to be able to set this adjustment if excessive fading is experienced due to locality. Adjust the receiver dial to a powerful station during the time of day in which it is received strongest. Then turn the neon adjustment until the light just fills the opening in arrow dial. Readjust the tuning dial of the receiver; should the light become more brilliant, leave the dial at the point of highest brilliancy and again readjust the neon indicator until it just fills the arrow opening. (This adjustment need be made only when the set is installed.)
Since the interstation noise suppression system or Q.A.V.C. is a proportional function of the neon light, the Q.A.V.C. system will be correctly adjusted.
Note that the neon light system is not intended to work on the short-wave stations. However, it will usually indicate resonance to more powerful signals.
Resistor X is an oscillator suppressor in short-wave band No.3. Its value is determined by individual requirements.
Locations of trimmer condensers in the new 19 tube all-wave superheterodyne. This illustration furnishes the necessary information to complete the data In the text.
Schematic circuit of the tuner chassis. There are 10 tubes in this unit. The 2·gang condenser mentioned in the text is located at the right of oscillator V17.
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.
Posted October 6, 2015