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 6BE6's 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 
be obtained.  If it is desirable to increase the headphone volume, 
an inexpensive lint 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 1/2 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 
should be installed using as short lead length as possible, and 
preferably mounted inside of the receiver bypassing each of the 
relay terminals to ground.

	We have recently received a few complaints advising that the 
slot depth control on the HQ-170 receiver is apparently 
inoperative.  This we can assure you is decidedly not the case, 
since from all indications, too much is being expected insofar as 
the effect of this control being very noticeable is concerned.

	The slot depth control is actually a very gradual vernier 
adjustment.  In view of this its effect will not be very noticeable 
unless the proper procedure is employed.  The suggested procedure 
is as follows:

Tune in an AM signal on any band or any other strong constant 
carrier of similar nature, such as crystal calibrator.  Whenever 
the receiver is being tuned for normal reception  be sure to first 
rotate the slot frequency control to the extreme clockwise or 
counter clockwise position.  In other words, never leave the slot 
frequency control at or near the zero setting.  If this procedure 
is not followed it is obvious that the center of the pass band will 
be slotted out, in some cases this being quite obvious by producing 
2 spot tuning or 2 peak S meter readings.

	After tuning in the constant carrier and peaking the S meter, 
taking the above precautions, rotate the slot frequency control.  
It will be noticed that upon approaching the zero setting, the S 
meter reading will be effected.  A very definite null or minimum S 
meter reading will be obtained with the slot frequency control 
adjusted at or near zero.  Observe this S meter reading.  With the 
slot frequency control set at the minimum S meter reading position, 
the slot depth control should be rotated very slowly throughout its 
range, observing the S meter.  It will be found that one particular 
spot throughout the range of the slot depth control a further 
reduction in the S meter reading will be obtained.  Once this 
setting has been obtained, the slot depth control may be left 
permanently in this position, and all future slot filter adjustment 
made by the slot frequency control only.  A check of the slot depth 
control setting may be advisable periodically.

	It is hoped that the above information will prove of interest 
and assistance.  If after following the various suggestions, 
trouble cannot be eliminated, please write to us supplying as much 
detailed information as possible in order that we may endeavor to 
be of further assistance or authorize return of the receiver for 
repair.  Please refer to terms of our warranty on the inside rear 
cover of your instruction manual which will apply under these 
circumstances.

	Erratic performance in the triple conversion bands, such as a 
temporary loss of gain after a period of transmission or stand-by 
operation, which is cured by rotating the band change switch or 
turning the receiver off and then on again, usually involved the 
second 6BE6 converter of V3 in the schematic diagram.  If changing 
this tube does not permanently cure this condition, changing the 
value of R10 from 22K to 47K is recommended.

	If a new 6BZ6 in the crystal calibrator does not result in 
improving the output of the crystal calibrator to your liking, 
additional output may be obtained by increasing the screen voltage, 
this is accomplished by merely adding an external « watt resistor 
from 47K to 100K across terminals or leads 3 and 4, of the couplate 
Z1 in the schematic diagram.

	If upon checking the 100 kc calibrator against WWV using 
another receiver it is not possible to zero beat the calibrator by 
means of the adjustable trimmer, and the crystal appears to be low 
in frequency, the frequency of the crystal can be raised by 
substituting an external 470K « watt resistor, for the one in the 
couplate Z1.  This is accomplished by unsoldering lead /7 of the 
couplate from one side of the trimmer and connecting the external 
470K resistor across the trimmer terminals.  This change will 
usually make it possible to zero beat a crystal that is too low and 
out of the range of adjustment provided by the trimmer.

	Please remember that the low frequency response of the 
receiver is increased when the audio gain control is employed at 
the lower end of its range.  This is the result of the auto 
response circuit.  Increasing the audio gain control setting to a 
position past straight up and reducing the RF gain will make it 
possible to obtain the same volume level with less low frequency 
response and usually better signal-to-noise ratio.  If it is 
desirable to reduce some of the low frequency response at the lower 
settings of the audio volume control, the auto response feature may 
be dispensed with by merely short circuiting resistor R47, 47 ohms.  
This results in removing the feedback which provided the better low 
frequency response.

					Very truly yours,

				THE HAMMARLUND MFG. CO., INC.

					Frank I. Lester, W2AMJ
					Sales Manager