This is by far the single most valuable piece of test equipment for servicing receivers and audio equipment. Built in meter for measuring gain of each stage under test. Easy to find weak or defective stages. Output speaker built in or to VTVM or scope. No line cord since it is self powered.
Model SE-350 Signal Tracer-ONLY $22.50
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Escalator — Part II
Since the original article on rf' SSB speech clipping appeared in 73 Magazine (p, 16, Dec*, I have received a number of in quiries relative to the construction of the clipper unit.
Resistors R3 and R4 in Fig. I should be interchanged (this was a printer's error). Replace the 300fi cathode resistor of V2 with one of 68H and the 47k screen resistor with one of 20k. At the grid input of VI the 22k resistor is omitted and a 140 pF A PC variable capacitor is substituted for the fixed 180 pF condenser for maximum tuning of the signal. Mount the mechanical filter topside with its midpoint baffle shield omitted-an original but later-proved unnecessary precaution.
It is important that the filter employed be identical to the one in the exciter unit, if the carrier frequency is not down on the filter skirt at or very close to that in the exciter unit, one of two undesirable things will take place: either the lower voice frequencies will be out of range of the passband and the audio will sound tinny, or insufficient sideband rejection of the lower clipped voice frequencies will occur with unwanted, newly generated frequencies. It may be preferable to extract the rf signal at the output of the balanced modulator rather than at the output of the following if stage. In place of the original Millen //transformer, llt try a less expensive one; T2 may be a Miller 912-C4 if transformer. The .01 mfd coupling condenser in the secondary lead of T2 may be left out.
The power supply can be placed on the same chassis with the clipper unit although a larger chassis, of course, will be required. Any power supply system that will deliver from 30 to 50 mA at a regulated voltage of 105 to 150V will be satisfactory.
i he following simplifications may be made: Omit the sub-miniailire switch, SI, and run the two RG-174/U coax input and output leads directly to the two jacks mentioned in the paper. A short coax-cabled jumper between the two jacks will restore the original exciter operation. Omit both the no-clip gain control and the DPDT switch, S2. Simply rely on the clip level control to adjust the amount of //clipping.
If excessive hum is encountered when clipping, it may, unfortunately, be necessary to shield the exciter's audio input stage.
Louis Herman, K6BW
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