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Hammarlund Manufacturing Hq-170a Communications Receiver Manual

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    Dear OM:
    This form is being prepared to provide prompt attention to a complaint as a result of trouble that 
    may be experienced in the field.  In addition to this we are supplying general information as a 
    result of inquiries previously received, that we are sure will be of general interest.
    Most troubles that develop in the field can be attributed to tube failure in one form or another.
    Unfortunately, it is impossible for us to eliminate tube troubles completely despite precautions 
    taken by us to do just this.  It is well known that tubes sometimes fail or change in operation 
    characteristics after a period of operation.  It can therefore, be assumed that despite every 
    precaution occasionally a tube will develop trouble and cause malfunctioning of the receiver.
    The most common complaint we have received is the high order harmonic output from the 100 kc 
    crystal calibrator.  This results in the crystal calibrator signal being weaker than normal, 
    especially on 10 and 6 meters.  This is usually due entirely to the 6BZ6 tube being employed in 
    the crystal calibrator position.  It is therefore, suggested that this tube be interchanged with 
    the 6BZ6 employed in the RF stage which may provide the increased crystal calibrator signal.
    Switching the two tubes in question will usually in no way result in degrading the performance of 
    the receiver since the tube formerly employed in the crystal calibrator position will usually work 
    perfectly as an RF amplifier even though it may not develop sufficient output when used in the 
    crystal calibrator position.  If switching the two tubes does not provide the desired results it 
    would be advisable to purchase another 6BZ6 for improved 100 kc crystal oscillator output.
    HUM
    Excessive hum in the speaker is usually the result of excessively high heater to cathode leakage 
    on the part of the noise limiter tube type 6AL5 or the 6AV6 tube employed as the first audio and 
    delayed AVC clamp.  If the hum is only noticeable when the receiver is in the AM position, the 
    chances are that this is due to a bad 6BV8.  If the level of the hum varies as the audio volume 
    control is advanced, this more or less indicates that the hum is due to a tube ahead of the audio 
    gain control, such as the 6AL5 or the 6BV8.  If the hum level remains constant regardless of the 
    setting of the audio control, this means that the trouble is after or behind the audio control and 
    the 6AV6 or 6AQ5 output tube should be suspected.
    HUM MODULATION OR DRIFT
    Hum modulation or hum frequency modulation that will be most noticeable on the 10 and 6 meter 
    bands, is usually due to a poor 6C4 high frequency oscillator or the first 6BE6 converter V2 in 
    the schematic diagram.  This condition will be apparent by the inability to obtain a near pure DC 
    or T9 note on 10 and 6 meters.  Changing the 6C4 high frequency oscillator usually corrects or 
    greatly improves this condition.  If a new 6C4 does not result in sufficient improvement, try 
    interchanging the 6BE6 employed in position V2 with the 6BE6 employed in position V5 or the 3rd 
    mixer socket.  Excessive drift which would be most noticeable on the high frequency bands, can 
    also be attributed to the 6C4 high frequency oscillator or 1st 6BE6 converter.
    VOLTAGE REGULATOR TUBE TROUBLES
    The first HQ-170 receivers produced employed a 4K 10 watt resistor as R-53 or the VR tube dropping 
    resistor.  This was later changed to 3K 10 watts to improve the voltage regulation.  In some cases 
    when the 4K resistor was employed, the VR tube would extinguish at maximum sensitivity control 
    setting.  Another noticeable effect would be excessive frequency shift as a result of varying _ of 
    the way on.  Changing R 53 from 4K to 3K at 10 watts will eliminate bot of these conditions.
    FAILURE OF THE HIGH FREQUENCY BANDS
    Failure of the receiver on any or all of the triple conversion bands can usually be attributed to 
    trouble in the second 6BE6 converter V3 in the schematic diagram.  This is usually the result of 
    low injection of the 2.580 MC crystal oscillator.  Obviously, the first suggestion is to try 
    interchanging 6BE6s or at least a new 6BE6 in this position.  If this fails to produce the proper 
    performance, a good VTVM that will not load the circuit, should be employed to measure the voltage 
    developed from pin 1 to ground.  A reading of 3 to 4 volts negative indicates proper performance 
    or injection.  Less than this voltage exceeding10, may be the cause of the trouble.  This can 
    usually be attributed to a defective 38uh RF choke L8 in the diagram, which may be open or have 
    shorted turns.  This trouble seldom develops but is a possibility that should be investigated.
    GENERAL INFORMATION
    Whenever the 500 cycle or .5 kc selectivity switch position is employed, for best results the side 
    band switch should be employed in the upper side band position.  Since this band width is only 
    employed and usable on CW, the BFO pitch or frequency control should always be employed plus or 
    minus approximately .5 kc for best CW performance.
    The headphone jack results in a deliberate mismatched to high impedance phones in order to reduce 
    the level supplied to them.  The lower the impedance of the phones, the more volume will usually 
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    be obtained.  If it is desirable to increase the headphone volume, an inexpensive line to voice 
    coil transformer is suggested.  This transformer is connected backwards with the voice coil 
    connections to headphone plug and the 500 ohm line connections to the phones.  The resultant 
    impedance step up will provide higher headphone volume.  This procedure should only be resorted to 
    when absolutely necessary such as when a person may be hard of hearing.  It should be remembered 
    that as a result of increasing the headphone level any residual hum will also be increased, which 
    the hard of hearing person will not find objectionable, whereas a person with normal hearing may.
    VOX CIRCUIT REQUIREMENTS
    In the event that the vox circuit in your transmitter may be designed for 500 ohm input and in the 
    event that sufficient gain in this circuit may not be available to provide proper performance from 
    the 3.2 voice coil winding, the matching transformer referred to in the headphone paragraph may be 
    employed.  Under these circumstances, the voice coil winding should be connected to the speaker 
    terminals with the 500 ohm line winding to  the Vox circuit. Such a matching  transformer may also 
    be required or useful for phone patch operation, depending, of course, on the design of the phone 
    patch.
    GRID BLOCK BIASING FOR VOX CIRCUITS
    Many of the single side band transmitters being produced today provide 100 volts negative bias 
    which is switched from the transmitter to the receiver by the Vox circuit.  The Hallicrafter HT 32 
    transmitter is a good example. As a result of the voice control operating the relay in the 
    transmitter, the 100 volts of negative bias available in the transmitter  is made available to 
    silence the receiver. When this type of receiver  silencing is desired the relay receptacle on the 
    rear of the HQ-170 is not employed. In order to adapt your HQ-170 for this operation it is 
    suggested that the two leads that are now connected to the relay receptacle be removed and each 
    one taped up so that they are insulated from one another and the chassis. This may be dressed 
    conveniently out of the way. A 5 megohm ½ watt resistor and 15 of insulated shielded lead is now 
    required.  One end of the 5 megohm resistor should be connected to pins 5 or 6 or tube socket V16 
    or the 6AV6. The other end of this resistor is then connected to the inner conductor of the 
    insulated shielded lead with the shield left floating at this point insulated to prevent shorting
    to the resistor, inner conductor, or any part of the wiring. The other end of this   insulated and 
    shielded lead should have the center conductor connected to one or both of the relay terminals 
    with the shield connected to any convenient ground or chassis connection.  The bias lead from the 
    Vox circuit is then connected to one or both of the relay receptacle terminals, a standard AC plug 
    may be employed in the relay receptacle. It is now necessary to employ a common ground connection 
    between the HQ-170 chassis and the transmitter chassis in order to complete the biasing circuit. 
    Making changes will result in the 5 megohm resistor being in series with the bias lead to the AVC 
    bus in the HQ-170. The 5 megohm resistor isolates the bias supply and prevents this lead from 
    affecting the AVC circuit.  The shielded lead is recommended to prevent RF pickup and is really a 
    precautionary measure. It may also advisable a shielded lead the receiver and the transmitter.
    This system in no way implies that the antenna changeover relay or a suitable TR switch will not 
    be required. Failure to employ one or the other may result in burning out the antenna coils of the 
    receiver, or other possible damage.
    Lab tests indicate that minus 75 volts will silence the receiver  when one volt of RF is applied 
    to the antenna terminals.  75 volts negative bias is therefore, the suggested minimum value for 
    complete silencing. The full bias voltage is not applied to the grids due to a voltage division 
    which takes place as a result of the 5 megohm resistor and the other resistors, employed in the 
    AVC system.
    DIAL CALIBRATION ACCURACY
    Please remember that we do not claim frequency meter accuracy.
    Our production tolerance on this receiver is plus or minus « a dial division.  This tolerance is 
    necessary as a result of working to printed dial scales.  The band edge markers are held to very 
    close tolerance, usually plus or minus the thickness of the dial marker.  The total runout or what 
    is often referred to as tracking error, will usually be within the plus or minus « a dial division 
    as previously specified.  It is for this reason that the adjustable dial marker and the 100 kc 
    calibrator is provided for the correction factors.
    RF FEED BACK
    In the event that RF feed back is experienced when the relay terminals on the rear of the HQ-170 
    are employed, this usually indicates that the relay leads between the receiver and antenna relay 
    are picking up RF.  This may be due to the particular lead length or a high standing wave ratio on 
    the antenna system.  The solution is of course, to prevent the RF pickup of the relay leads from 
    getting into the receiver.  Adding a pair of .01 disc ceramic capacitors from each of the relay 
    terminals to ground will usually eliminate the feed back condition.  These extra .01 capacitors 
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