Wextark Radio, Inc. 7 Tube Schematic

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Product Information:
Model:7 Tube
Manufacturer:Wextark Radio, Inc. (Allied Radio)

Schematics Content:

Page 1:

KNIGHT 7 TUBE SUPERHETERODYNE 1932 MODEL

These readings are only comparative and are not true voltages applied. Tho voltmeter, when the readings are taken at these points, is in series, with a very high resistance. To read the 247 bias, read between H.K. speaker socket and ground.

Page 2:

KNIGHT 7 TUBE SUPERHETERODYNE

1932 MODEL

INTERMEDIATE TRANSFORMERS:
To intermediate transformers are of the band pass type and or exceptionally high uniform gain.
The y are tuned to 175 kilocycles, The interne di ate frequency, trimera and mounted on an isolantite base, preventing the transformer from becoming de tuned due to the trimmer condensers absorbing moisture or warping. For this reason it should rarely, if ever, be pe cossary to re-track the intermediate froqueno trimers. In the event that it should be advisable to re-align the in terme dia te frequency co118, 1t is absolutely essential that a 175 kilo cycle oscillator and an output measuring device be used.

ALIGNMENT OF RECEIVER:
Because of the construction and thorough Impregnation of the intermediate coils, the intermediate stages should rarely need re-tracking. Only when an intermediate coil has become defectivo duo either to an open or burned out winding, should it be necessary to re-adjust the intermediate trimmer. Should this occur, 1t is necessary that an oscillator be used and to intermediate trimmer be adjusted at 175 kilocycles. To align the intermediate stages, connect the high side of the oscillator output to the grid circuit of the first detector, which is done by disconnecting the grid cap of the 224 Arst detector and connecting the high side of the test oscillator to the control grid of this tube. The ground side of the test oscillator should be connected to the ground post oz the cha 8818. Set the oscillator at 175 kilocycles and adjust the output of the oscillator so that a convenient reading is obtained on the output meter. Be sure that the output from the oscillator is not so large that it will overload the second detector. If during the alignment the meter goes off scale, reduce the output of the tost oscillator or adjust the receiver volume control. The trimmers of the intermedia to colls are accessible through the small holes in the top of the intermediate shield can. There are two trimmers to each intermediate coil. Align the grid triter of the tst intermediate coll. After & maximum reading is ob tal nod by adjusting the grid trimmer on the first intermediate, adjust the primary for maximum reading and then re-check the grid side to make certain the alignment of the secondary has not been changed by the adjustment of the primary. The same procedure is followed in aligning the second intermediate coils. After both interne diato coil. are properly aligned the adjustment of the intermediate stage is complete and they should not be further disturbed.

Replace the grid cap on the first detector and connect the oscillator output leads to the antam and ground posts of the receiver and set the oscillator at 1435 kilocycles, Then tune the receiver to 1435 kilocycles on the dial. It is important that the receiver be tuned to this point, Ir the receiver is out of the cabinet It will be necessary to use some temporary Indicator so that the position 1435 kilocycles on the dial may be accurately located. (This inii a tor should be set so that men the variable condenser: are at the maximum capacity stop the indicator points to the last 110 on the dial at. the lor frequency end.) Then track the variable condensers by adjusting the trimmer condensers in the following order: Oscillator antenna and radio frequency - (reading from the front of the receiver toward the back, the variable condenser sections are: Oscillator, antenna and radio frequency). After the variable condensers have been properly tracked at 1435 kilocycles, adjust the oscillator to 1295 kilocyclos. Tune the receiver to this frequency. Check alignment of the condensers at this point by bending the end plate of the rotors in and out, noting the chango in reading on the output me ter. Ir when the plates are bent is the reading is increased, it is an indication that that particular section requires moro capacity and the end plate should be permanently bent in at this point; or, it when the Dd plate is bent away, the reading is increased, the ond plate should be bent away permanently, as it is an indication that that particular section requires less capacity at that particular point. The variable condenser & should be checked in this manner at 1295, 880,650 and 550 kilocycles. These points have been chosen so 88 to take advantage of the slots in the end platos of the variable condenser 8, Th is procedure of bending plates should rarely be no co ssary on the 08cilla tot section, as the plates of the oscillator section are specially designed to properly track over the broadcast spectrum, providing the antenna and radio frequency stages are correctly aligned.

ELECTRO DOMIC SPEAKER: The electro dynamic speaker has a tapped field winding-qe section of what ch is 1320 ohms and is utilized as the second choke in the filter circuit. The other section, which is 300 Ohms, is used to obtain the proper bias for the 247 tubo, as well as acting as an additional filter choke.

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