MODEL ACP-1 KIT $18,50

30i db compression range ■ Low-noise FET input stage m 5-transistor and 1-diode circuit ■ Adjustable input and output levels ■ Printed circuit construction with easy-to-follow instructions ■ 3-way jacks for PIT operation • Easily installed in mike line

Other Kits Audio Amplifiers » Power Supplies ■ Test Equipment * Treasure Locators ■ and many others

FREE Date sheets with circuit description, diagram t and specifications for aft kits*


P.O. Box 327 ■ Upland, California 91766 Phone 714-965-1540

The brass eyelets are inserted into all of the No. 43 holes in the component boards from the component side. Make certain the eyelets are pushed all the way into the board, so that the eyelet head is against the surface oi the board, "urn the component board over, lay it on a piece of wood and funnel out each of the protruding eyelet 'barrels1 with a few gentle taps of a hammer on a 3/8" center punch, I used GC Electronics No, 7251 eyelets and a 3/8" punch identified as TROTO 4i\

All wiring is done on the back of the component boards in point-to-point fashion with No, 22 AWG tinned bus-bar wire. Insert the wires through the eyelets and bend the ends of each wire over on the component side of the board to hold the wire in place. Clip each wire next to the eyelets on the component side. Insert the components and solder each eyelet from the wiring side. Clipping off the excess component leads completes the component board wiring, phe leads of all the semiconductor components should be heat sinked during the soldering operation.

Checkout and Adjustments *

After the construction phase is complete, two pairs of electrical adjustments are required to place the unit in service:

a) Rll and R12 must be set so that the gates operate as amplifiers-

b) LI and L2 must be adjusted (turns removed) to set the exact mark and space operating frequencies.

Connect a 600 ohm (nominal) load and oscilloscope to J3 and set R11 and R12 (on

Component boards 1 and 2 are located as shown. The third board is mounted on the other end of the chassis, opposite CB2-

CB2) to the approximate center of their range. Apply power to the unit and check the minus 3,6 and minus 8.2 voltage levels. Set the mark and space amplitude controls (R9 and RIO) to about mid-range and the af output level control (R15) fully clockwise,

Place the mark keying selector switch (S4) lo 4ton" and the space keying selector switch (S3) to *Loff'\ DSI should be illuminated and DS2 extinguished. Set the mark amplifier bias by adjusting Rll for maximum amplitude of the mark signal as displayed on the oscilloscope. Maximum amplitude and minimum distortion occur simultaneously.

Place the mark keying selector switch to "off" and the space keying selector switch to "on1", DSI should be extinguished and DS2 illuminated. Adjust R12 for maximum space signal amplitude as observed on the oscilloscope-

Set the internal/external keymg switch (S2) to "external". Key the unit at J1 or J4 and check each of the possible keying combinations listed in Fig. 3. The responses of DSI and DS2 should follow the signal output. Place S2 to "internal^ and observe that the internal keying signal keys the unit at about a 22 Hz rate. The synch output signal at J2 should be a 22 Hz square wave at this time. This frequency has no particular significance other than being at about the same rate as the keying frequency of a 60 speed machine. If it is too far off, bring it in by changing the value oi R18+ Bear in mind that each different set of components will have its own frequency vs. R18 characteristics .

Because of the capacitor and inductor tolerances, it is extremely unlikely that the mark and space frequencies will be correct. I he frequencies will probably be too low, but can be set to within a few cycles by removing turns from LI and L2. Go easy here - it's a lot easier to keep on removing turns than it is to start adding them back. The frequencies may either be compared with an accurate audio (or AFSK) oscillator or measured with a frequency counter. The mark signal should be at 2125 Hz and the space signal at 2975 Hz. Soldering iron heat conducted to CI, C2, C4, or C5 will affect the oscillator frequencies. Frequency measurements should be made only after the capacitor temperatures have stabilized.

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