Knight Electonics Corporation- SPAN MASTER

1958 Knight Span Master

Regenerative .54 to 30 mc Receiver Kit

From the Span Master Instruction Book

INTRODUCTION

In a couple of evenings you can build the Span Master and hear thrilling foreign shortwave broadcasts from all over the world. The Span Master is a Regenerative type receiver which covers regular programs on the standard broadcast band as well as short wave, including American and foreign broadcasts, amateur phone and code transmissions, ships-at-sea, and aircraft.

A convenient band switch gives you instant choice of any of 4 bands, providing continious coverage from 540 to 30 mc. Calibrated electrical bandspread simplifies tuning the crowded shortwave bands. In keeping with the high quality of the comonents and circuit, the Span Master is transformer-powered and uses an efficient selenium rectifier.

The professional, contemporary styling of the cabinet makes this a receiver you'll be proud to display. The dials are clearly marked in white against black for added tuning ease. The panel is anodized aluminum.

FEATURES

SPECIFICATIONS

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CHECKING YOUR KIT

Before starting to build this kit, check each part against the parts list on page 18. The wiring pictures in this book will help you identify the parts. Symbols used to give the value of the parts are omega sign for ohm, K for 1000, Meg for one-million, micro sign for micro or one-millionth, and fd for farad.

Keep the different sizes of screws and nuts separate, for convenience in building. The thinnest screws are #4 and the thickest are #10. The six that look like woodscrews are self-tapping screws.

CONSTRUCTION HINTS

The only tools necessary for building your Span Master are: A soldering iron rated about 27 watts, long-nose pliers, diagonal cutters and a screw-driver.

To mount a resistor or capacitor, pull the leads through the terminals so the part is tightly mounted. Then bend each lead around the terminal and cut off the excess wire, as shown in Figure 1.

The flexible tubing supplied with the kit is called "spaghetti". It is used to cover bare wires and leads where there is a chance they will touch other bare wires or the chassis. When spaghetti or bare wire are specified, cut a piece of the needed length.

Use only the color of wire specified in the instructions because the colored wires have been pre-cut to definite lengths.

HOW TO CARE FOR YOUR SOLDERING IRON

Your soldering iron is the key to good soldering since it supplies the essential ingredient- HEAT. If the tip is covered by a dirt (oxide) film, the iron will not be able to transfer its full heat. A new tip can be protected from film by coating it with solder the first time it is heated.

Never use the iron like a brush- soldering is not a paste-spreading operation. To get the most heat out of the iron, always press the iron firmly to the connection. Hold it so the greatest tip surface is directly in contact with the connection.

The assembly instructions have been omitted

UNDERSTANDING YOUR RECEIVER

As you develop skill in operting your Span Master, you will learn how to bring in stations from amazing distances. Understanding your receiver helps you to develop the necessary skill.

THE ANTENNA

The antenna brings into the receiver signals covering all bands. The better the antenna, the stronger the signal fed the receiver, and the greater the number of stations that can be received. Figure 12 shows how to install a good antenna.

TUNING

Since the antenna brings in all signals within its range, the receiver must select the desired station and reject all others. This is done by the tuning section, whech consists of the Band Coils, L-1, L-2, L-3, L-4 and the Tuning Capacitors C-1 plus C-2.

BANDSWITCHING

The station selected (tuned in) changes every time the settings of the capacitor changes or a different coil is selected. You can tell the coils have different electrical values by the number of turns of wire. Band A coil has the most turns and is used to tune in stations on the lower frequencies. Band D has the fewest turns and is used for the highest frequencies. The BAND SWITCH S-1, selects the desired band coil.

MAIN TUNING AND BANDSPREAD

After the BAND SWITCH selects the desired band coil, you can tune the exact station you want by adjusting the tuning capacitors. the electrical value of the capacitors changes as your open or close the plates. Main Tuning is done witih C-1, because a big change of capacity results from opening or closing the plates just a little. Fine tuning is done with C-2, called the BANDSPREAD.

DETECTION

Only part of the station's signal contains the desired program (music, sound, etc.). this part rides on a crrier wave used to carry the program far greater distances than the audio (sound) signal could otherwise travel. Once the signal is received the part of the signal which conveys the program must be separated from the carrier and then amplified (enlarged). In v-1, the 6BZ6 tube, the carrier wave is removed and the desired portion of the signal is DETECTED.

REGENERATION

This feature of your receiver allows you to receive even very weak signals. It is like a controlled snowballing action, getting bigger and bigger, until the desired signal strength is reached. Too little would make it too weak.

Regeneration takes place in the V-1 6BZ6 tube circuit, with the signal amplified in the tube. It is taken off the screeen (pin 6) and fed back to the grid (pin 1) of the same tube through the feedback circuit of C-7, S-1, the BAND COIL and C-4. The amount of feedback or regeneration is controlled by REGENERATION and FINE REG.(REGeneration) controls. These controls act by raisiing or lowering the screen voltage.

The REGENERATION control is always used first to give the approxiamate amount you want. FINE REG. is used for fine adjustsment, during the shortwave tuning. It is important to remember that the amount of regeneration varies when station frequency is changed, and the FINE REG. must be readjusted to maintain regeneration.

AUDIO AND POWER AMPLIFIER

V-2, the 6AW8 dual tube, combines these two functions. The audio amplifier section increases signal voltage to make it large enough to drive the power amplifier section. The audio power is then delivered to the speaker or PHONES. The amount of signal is controlled by R-10, the VOLUME control used for private listening (phones).

POWER SUPPLY

The power supply is AC operated (transformer powered) for greater safety and circuit efficiency.

HOW TO USE YOUR SPAN MASTER

ANTENNA, GROUND & AC POWER CONNECTION

See Figure 12. Connect a single wire antenna to the terminal stamped "A" on the back panel. A good antenna is all important. In some areas reception can be improved by connection a ground wire to a water pipe or a ground rod.

Plug the line cord into an outlet supplying 110-125 volts, 50-60 cycles AC ONLY. DO NOT ATTEMPT TO OPERATE FROM DC POWER.

BAND "A" (STANDARD BROADCAST)

Turn BAND SWITCH to "A", OFF-VOLUME to the middle of its range, and BANDSPREAD all the way to the right. Set the Main Tuning Dial to the desired station on Band A. Be sure SPEAKER-PHONES switch ion the back is set to SPEAKER, unless you are using phones.

Gradually turn REGENERATION to the right until a rushing sound or a whistle is heard. Stop here. This is the most sensitive point, where the receiver has just begun to oscillate (regenerate).

Slowly turn the Main Tuning dial tothe right or left as needed, to make the whistle lowerin pitch, until a very low-pitched sound is heard.

VERY SLOWLY, turn REGENERATION control to the far left until the whistle just disappears and the station is clearly heard. Adjust VOLUME for comfortable listening.

Turn receiver OFF when you are through using it.

BANDS B,C, or D (SHORTWAVE)

The main difference between standard broadcast and shortwave tuning is that the full sensitivity of the receiver is needed to tune in distant shortwave stations. This is achieved by careful setting of the REGENERATION and FINE REG. controls. Tuning is also more critical on shortwave bands and fine tuning mustbe done with the BANDSPREAD. A GOOD ANTENNA IS A MUST FOR SHORTWAVE RECEPTION.

Turn OFF-VOLUME all the way to the right, BAND SWITCH to desired band, BANDSPREAD at "5", FINE REG. at the middle of its range and MAIN TUNING to the desired range of stations.

Turn REGENERATION slowly to the right until a rushing sound is heard. This is the desired setting. You can check the correctness of this setting by turning the BANDSPREAD through its range- a sound of "birdies" should be heard. If instead of "birdies" you hear a constant whistle, REGENERATION has been turned too far and should be turned back to the left, slightly. LEAVE BANDSPREAD at "5".

Tune the desired station as well as possible with the MAIN TUNING.

Tune station is clearly with the BANDSPREAD, trying either to the right or left of "5".

If necessary adjust FINE REG. for better reception.

TUNING ACROSS SHORTWAVE BANDS

Turn Main TUning to the desired station, BANDSPREAD to "5". If the set sounds dead (no rushing or whistling sound) turn FINE REG. to the right. If there is too much regenertion (constant whistle as you tune the band) turn FINE REG. to the left until the whistle just disappears. For code reception set where the whistle just begins. Tuyne the station in clearly with the BANDSPREAD.

SERVICING HINTS

If the tubes fail to light, or the receiver sounds "dead", turn the set off and remove the line cord from the power outlet. Take the receiverout of the cabinet and carefully inspect all wiring for correct connection and good solder joints. Most cases of kits failing to operate are caused by a wiring error or poor soldering. Especially check all solderiing to ground points, such as solder lugs and the heavy bare wire.

If the receiver operates on some bands, but not all bands, check the wiring to the band coil for each inoperative band. Terminals on S-1, the BANDSWITCH, must not be accidentally shorted together by bare wires or lumps of solder.

The receiver may sound "weak" if it is not connected to, a good antenna. See Figure 12 for an illustration of an effective single-wire antenna.

NOTE: Figure 12 not shown in this WB6FZH article.

Last Updated: January 15, 1999

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