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#1
12-15-2008, 07:53 PM
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Question about my Hammarlund
As a few of you might be aware, I acquired my first (in a very long time) "real" communication receiver from the E place. It arrived slightly dented, but perfectly functioning. I'm having a lot of fun with the old man - actually, I'm 2 years older than it is so it's not that old
 ...Anyway, I've noticed a slightly odd behavior with the S meter: it reads signal strength and varies as the signal waxes and wanes in strength, but when there is no signal at all, the meter "pegs" at the low end of the scale. I've already precisely followed the procedure for zero-adjusting the meter as per the owner's manual, yet the meter still drops below zero in the absence of a signal - and only when the unit is ON. I would consider the possibility that I had overcompensated with the adjustment screw if the meter did that while the unit was OFF, but while unpowered, the meter reads at precisely zero. What might be happening in the guts of my old 145X to pull the meter below zero?
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My original compositions on my podcast 
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#2
12-15-2008, 08:05 PM
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There must be some kind of "electronic zero adjust" for the DC amplifier that drives
the meter. Getting a service manual is a must for this. Maybe someone who has the proper documentation could post an excerpt of the schematic showing the relevant area. Good luck.
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#4
12-15-2008, 08:19 PM
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Yeah, Sandy. It works, but I can't help but question the signal strength of a station's carrier if there's something of a negative voltage "fighting" with the voltage driving the meter.
One other thing: as I rotate the SENSITIVITY control CCW (tuned to a strong station or not), the meter will do the neg-peg thing as I approach minimum sensitivity, then come back to perfect-zero when the SENSITIVITY control is completely reduced to minimum.
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My original compositions on my podcast
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#5
12-15-2008, 08:25 PM
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Quote:
control voltage on the same AVC bus that provides the signal to the meter. Of course, the fact that the meter goes off range still needs to be fixed. The normal setting for the sensitivity control on a communications receiver is maximum, it should be backed off only when receiving a very strong station that is overloading the receiver.
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#6
12-15-2008, 08:45 PM
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Well, all I know is that meters can be REAL PITAs if they don't wanna gee & haw just right...I fooled w/one on one of my R-390As for the better part of an afternoon, doing what "The Book" said, & NEVER did get it to suit me...
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Benevolent Despot
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#7
12-15-2008, 09:50 PM
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Quote:
There is a complete manual for the 145X at bama if you don't have one. After mechanically zeroing the meter with the set off you short the antenna input terminal to the ground terminal. Turn the set on and let it warm up for at least 15 minutes. Then adjust R24 until the meter reads zero. The receiver will still exhibit the negative reading the in the future until it warms up fully. But once it does, it shouldn't read negative. It is sensitive to the aging of V4 and V5, the 6BA6's, because it basically measures the difference in cathode currents of the two stages. If that IF stage is misaligned you can get even weirder results. John
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#8
12-18-2008, 07:31 AM
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If you haven't gotten the answer here...
Go to mailman.qth.net , select "Directory of Email Lists" from the menu on the left, page down to "Hammarlund" and follow the directions to join the list. Another one of more general interest is "Boatanchors".
There are many knowledgeable people on these lists who will be happy to help you. Harry, KT4AE Maryville, Tennessee "Mostly Hallicrafters and Dynaco"
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