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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 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
hq170.txt (15 KB)
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