Tempo I Cl

• Frequency Range: 146-148 MHz

• Same general specifications as CL 220

• Output Impedance: 50 ohms unbalanced.

• Sensitivity: 0.5 microvolts nominal for 20 db quieting.

• Spurious & Image Attenuation: 70 db below desired signal threshold sensitivity.

• Adjacent Channel Selectivity (15 KHz channels): 70 db attenuation of adjacent channels. 1

• Type of Receiver: Dual conversion superheterodyne.

• Audio Ouiput: 2 Watts minimum w/internal speaker (at less than 10% distortion)

destroyed the micas in the higher power version. Figure 5 is the photo of the model being described. As usual, the largest single component is the heatsink. The one shown is minimum in size for the rating. Since Ihe heatsink could he secured to the case of the equipment, additional cooling would be available. Figure 6 is the four-in-series string which delivers 200W CW output. Figure 7 is the piioto and, of course, is the experimental

Fig. 5. 755V amplifier. Note heatsink size.

version. In both models the input circuits use a toroid made of ferrite cores by Amidon. For best efficiency, the driver stage would have the link secondaries wound over the primary; eliminating capacitor and toroid. A 50£2 output from the driver made development much simpler. Power measurements were made using a Bird wattmeter and dummy load. The driver was adjusted to deliver a maximum of SW at 7.1 MHz. Driver turns ratio to primary was 5:1, but was not critical. Multicolored solid conductors proved to save time when wiring to the bases. All windings were the same in number of turns and polarities of phasing.

When the first model was made, all driving circuits to the base were series fed. About the only thing good about that connection was the self-oscillation. Simply by making the base shunt fed. the oscillation was stopped.

Here are some suggestions that may be of help in designing an amplifier that will operate as it should. I have seen as much as a 50% loss in power when the contacts were not as they should be.

1. All connections should be made with a mechanical contact, if possible with a copper strap. Then the joint should be soldered to prevent later corrosion.

2. Low resistance is a must in all circuits carrying rf, dc, or both. Don't take any chances with components when connecting to the heatsink or some other contact.

3. The conductor size should be large for best results. If a solenoid coil is used for the final, the wire size should be No. 9 or 10. If the toroid type is used. 3 sizes smaller will have the same rating when both windings are connected in multiple.

4. The number of turns is important in the tank coil if maximum output is desired. There is also the need of matching the load with the output. If a pair of ferrite toroids are used and wound as one core, the output will be reduced slightly but there will be space savings which may be unportant.

5. F.ach transistor should be balanced with the adjustment of the forward biasing resistor. When all are balanced for the same static current, the correct voltage division takes place and the dissipation should be reasonably uniform, as well as providing better linearity.

6. Do not be stingy with heatsinks! Operate the transistors coo! if you want long transistor life. Blowers or fans can reduce the need for large heatsinks but there is the noise and other problems from the vibration and size of the cooler.

7. The use of silicon thermal lubricant is recommended, plus the secure mounting of the heatsink of the transistor to the heatsmk.

8. The tLineup should be done with a variable rf source. Do not tune up at first with more than a few watts. The dc supply

Fig. 5A. Toroid winding details for tank and driver coils.

Jo EmmeU Jennings W6EI/KH6HLN 1007 Freedom Blvd. Watsonville CA 95076

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