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1-10 of 19 messages
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Are alignments really necessary?
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by K3STX on October 18, 2009
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Just wondering, since "it it ain't broke, don't fix it" seems to be a mantra around here. I have an SX-71, it seems to work "fine", but I have no idea if an alignment would help sensitivity/selectivity, etc... I hesitate to start messing with it since I could easily make it WORSE than it is now! I'm not technically inclined. All I have is an old Simpson signal generator for alignment.
If the rig seems to be working "fine", do you guys just leave it as found and make due? I have no idea how well this radio is "supposed" to work. It worked well enough for a QSO tonight with Italy on CW on 40 with a dipole and DX-20, FWIW.
paul
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RE: Are alignments really necessary?
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by KE3WD on October 19, 2009
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If a receiver is involved, can you line it up properly with WWV?
Realistically speaking, alignment of other sections *may* help, albeit only slightly if the thing is on frequency and working already. Beware of "alignments" performed by those not experienced and in the know or done without the proper calibrated alignment test equipments, for that could easily result in degraded performance or no performance at all.
Good test equipment, thorough knowledge of the unit's circuitry, a copy of the Service Manual, which has been studied thoroughly beforehand, an experienced technician should be able to ascertain if the device is within spec or not. Knowledge of the Signal Generator, possession and use of attenuation inserts along with the knowledge of what they do and when to use them, experience in tuning various types of alignable circuits, all come into play here. For example, the simple Zero Beat is something that most noobs seem to have trouble dealing with until the light bulb comes on.
Even given all that, experience has taught me not to touch alignment of circuits in older gear that are performing properly.
My rule of thumb is to only perform an alignment of the circuit under repair at the time. For example, if I troubleshoot a rig and find a bad component in a section, upon replacement of that component I will align *only that section*. Often is the case that restoring the component parts to spec means that any alignment done will be slight to none at all, too, depending upon the type of failure.
My recommendation to you is to enjoy the rig in operation as-is, only cross bridges when and if they actually appear in front of you. But I tend to view the process from the standpoint of the budget. Others who are into total restorations may think otherwise. They should be prepared for the possibility of testing and replacing many borderline components first, in a lot of cases, plus they should have the experience and equipments as mentioned above if they are going to achieve meaningful reults IMO.
Anything else is likely to fall under the "Golden Screwdriver" heading.
--KE3WD
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RE: Are alignments really necessary?
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by KE3WD on October 19, 2009
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If a receiver is involved, can you line it up properly with WWV?
Realistically speaking, alignment of other sections *may* help, albeit only slightly if the thing is on frequency and working already. Beware of "alignments" performed by those not experienced and in the know or done without the proper calibrated alignment test equipments, for that could easily result in degraded performance or no performance at all.
Good test equipment, thorough knowledge of the unit's circuitry, a copy of the Service Manual, which has been studied thoroughly beforehand, an experienced technician should be able to ascertain if the device is within spec or not. Knowledge of the Signal Generator, possession and use of attenuation inserts along with the knowledge of what they do and when to use them, experience in tuning various types of alignable circuits, all come into play here. For example, the simple Zero Beat is something that most noobs seem to have trouble dealing with until the light bulb comes on.
Even given all that, experience has taught me not to touch alignment of circuits in older gear that are performing properly.
My rule of thumb is to only perform an alignment of the circuit under repair at the time. For example, if I troubleshoot a rig and find a bad component in a section, upon replacement of that component I will align *only that section*. Often is the case that restoring the component parts to spec means that any alignment done will be slight to none at all, too, depending upon the type of failure.
My recommendation to you is to enjoy the rig in operation as-is, only cross bridges when and if they actually appear in front of you. But I tend to view the process from the standpoint of the budget. Others who are into total restorations may think otherwise. They should be prepared for the possibility of testing and replacing many borderline components first, in a lot of cases, plus they should have the experience and equipments as mentioned above if they are going to achieve meaningful reults IMO.
Anything else is likely to fall under the "Golden Screwdriver" heading.
--KE3WD
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RE: Are alignments really necessary?
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by KE3WD on October 19, 2009
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This forum software or this server is in need of an alignment, though.
Freezes and then double-posts.
And does it quite often.
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RE: Are alignments really necessary?
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by AA4PB on October 19, 2009
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Without the necessary test equipment and some experienced help I wouldn't attempt a full alignment if it is working okay now. Even an experienced shop wouldn't start "turning screws" until they made measurements to determine that it was not meeting factory specifications.
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RE: Are alignments really necessary?
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by K3STX on October 19, 2009
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Thanks, it receives WWV just fine and I THINK the tracking for frequency is OK, to be honest all I really care about now are the 40 and 80 meter Ham bands. I might build a 100 kc crystal oscillator just to know where band edges are, but that's about it.
I read everywhere "she will be great with an alignment" but think leaving well enough alone is the way I will go. Maybe later, with more experience I will try it.
paul
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RE: Are alignments really necessary?
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by K4DPK on October 20, 2009
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There is only one place where alignment may possibly be of some benefit, and even that will probably be minimal.
You might see some improvement in sensitivity by touching up the trimmers for the RF amplifier. These are affected slightly by different antennas and different parts of a band, because this rig has no front panel antenna trimmer.
Phil C. Sr.
k4dpk
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RE: Are alignments really necessary?
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by K8AC on October 20, 2009
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In a receiver of that vintage and design, you can be sure that tuned circuit components have changed values to some degree and it's a good bet that the dial calibration is not what it could be. The alignment of the SX-71 isn't complicated and a basic signal generator should do the job, but you might want to check the calibration of an older generator against a modern receiver first.
While opinions differ on this, I always replace all the molded and paper/wax caps and electrolytics before doing anything else. It makes no sense to me to trouble shoot a number of problems resulting from leaky caps as that can be especially difficult particularly when you have more than one failure at a time.
Plus, you probably have no idea what the previous owners may have done to the receiver, including adjusting coils, etc. without proper equipment or knowledge. So, you can't assume that the alignment is anywhere near correct as-is. If you're happy with it as is, do nothing. But - be prepared for problems if you don't replace at least the filter caps in the power supply.
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RE: Are alignments really necessary?
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by K3STX on October 20, 2009
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I'm a rebel, and I'm gonna live life on the edge! The filter caps are original and I have no evidence of problems in them. Call me crazy, I'm a'gonna fix it only when it breaks.
I checked today, the dial scale is a bit off (consistently about 1 mm too low on the dial, I have no desire to try to figure out how to move it). It is good enough for me to have QSOs with guys using my measly 30 watt DX-20: how sensitive does it have to be?!
paul
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