mORE BON PIRBS
    
    Correction- The 39K resistor us~d for #ttlng
    the gain of the ampllfier ln last month's is-
    sue is incorrect. It should be batw~n 5 and 6
    thousand oluns in valne. Too large a velne will
    cause a buzz in the ampllf$ar from too much gain.
    
    l~et's clear up a few details in last month's
    Blne Box constzuction plans. For those of you
    without a lot of test equtptment, th$s might help
    you a bit.
    1- The Twin T oscillator has maximue stability for
    voltage and temperature changes-when it is tuned
    at least 5X above the initial osai~ating frequency
    of the oscill~. Othen~rise, a voltage drop of a
    volt or temperature drop of 20 degrees might turs~
    it off. For example, tune in your resistor or cap-
    acitor velues of the 1100 cycle oscillator so that
    it starts oscillating at about 1000 or 1050 cyoles,
    and tune it up to }100. The starting point of osc-
    illation is always the purest sine wave, but the
    oscillator is on the verge of turning off, so a
    slight distortion of the wave can and must be tol-
    erated ~n this circuit.
    2- Tuning up to a tauch tone phone(freruencies given
    last month) will result in greater tl~n LX accuracy.
    A hammond organ should be even better. The MF rec-
    eivers that process your calls will respond to an
    error of 30 cycles or greater with a rsorder signal.
    That's a wide margin, and it varies from place to
    place. So if your tones come closer than 30 cycles
    to the correct ones, you will have better success
    and less of "I'm sorry, your call did not so thru~.
    3- Repeat-Call only fram psy phones, never fran
    your home phone! An exception is to call fron' a
    phone that wi 11 probably never be boxed on again.
    The phone company has records of 800 calls and
    555-1212 calls that are abnormally long, and they
    have been known to investigate.
    4- If your call doesn rt go thru, it may be your
    tuning, an excess of distortionttones will sound
    very harsh),too loud or soft a tone, extra ncise
    leaking into the phone, and most important, an
    overload in Bell's circuits that night from all
    the other blue-boxers making calls. Also remember
    that if you initially dial and beep of f a 800 or
    information number in the area code you will be
    boxing, do not key in the area code, ~ust the 7
    digits( 7D) .
    5- The diodes are non~critical, small signal units
    and don't have to be 1N914. The transistors are
    small signal NPN type wich HFE of 50 or more The
    transistors mentioned, and rnany others also will
    all work perfectly.
    
    sq.uare wave, generated by an on~off type
    of device such as a multivibrator, has a
    lot of harmonics, sounds harsh and is not
    as effeccive as a sine wave, though often
    easier to make.
    
    .N
    
    \
    
    A pure s~ne wave, fran a Twin T oseillator, and
    from ~ tauch tone phone is the best waveshape
    for ac~civating Western Electric~s brain.
    
    A Twin T oscillator slightly distorrted, because
    it is tuned SX higher than its initaal frequency
    of oscIllation. Its stability is excollent. It's
    dynarr~ite for boxing.
    
    A
    
    /

    





    
    \
    
    ~/
    
    A triangle wave, generated by the Signeties
    566 IC(Integrated Cireuit). Because it isn't
    a pure sine wave, it sounds harsh because it
    contains harrnonics, and it doesn't work as
    well, thou~h it does work.
    
    This is a sine wave with its peaLs flateened (or cut
    off). It causes distortion, harshness, and trouble. A
    telephone earpiece has a dual diode connected across the
    terminals in newer units, and if the signal lavel is too
    gr~eat the diodes absorb the peaks of thc slne wave, thus
    causing the wovefonn to distort l~e this. Remove the
    dioc~e before using.
    
                     1' '1
                     r~_s
    
         ~_e