[Boatanchors] Tuning a Boatanchor?

[WQ9E at btsnetworks.net]

Bob,

Start by making sure that the dial/capacitor is properly indexed before you start the alignment.  Usually the manual will tell you exactly where the pointer should rest with the capacitor at full mesh.  Also make sure that the bandspread capacitor is properly indexed (usually full open at the "set" point).

Did someone before you make excessive use of the split segments of the capacitor?  Many vintage receivers allow "knifing" the capacitor to somewhat modify the rate of change and if these are used to extreme it will make proper calibration impossible.  If they are severely bent I would return them to "neutral" (being very gentle when you bend them back.

Is the rotor properly centered between the stator plates?  With the capacitor at full mesh, look straight down to avoid parallax error and make sure it is properly centered.  If it is off you can generally correct it with a minor adjustment of the thrust bearing.  This would also be a good time to clean and relube the thrust bearing.

Most receivers do you high side injection and most manuals will either specify this or where the image should appear when properly aligned.  It is easy on the upper bands to have the receiver tracked on the wrong side with 455 Khz IF single conversion receivers.  I use a modern portable digital SW receiver (a Grundig YB-400 in my case) to set the oscillator calibration.  You should hear it in the receiver at the dial frequency plus the IF (assuming high side tracking).  I set  a couple of memories for the high and low end of the band and this makes it very quick to set the oscillator calibration; adjust RF and mixer tracking with your signal generator as usual.  If the calibration is way off I would suggest setting the trimmer for half mesh and tune the receiver to the center of the band.  Then adjust the coil until it comes into calibration.  This will give you a good starting point if it was way off and will allow much quicker iteration to the final calibration.

There is a lot of variance in accuracy across receivers.  My SX-88 is very close across the range as are my National NC-183 and 183D but I don't think my SX-25 or SX-24 will ever be great across the range.   Some receivers really need a calibrator with selectable 1 Mhz. and 100 Khz. markers for fast setting.

Rodger WQ9E

----------------------------------------
From: Bob Macklin <macklinbob at msn.com>
Sent: Sunday, November 07, 2010 1:41 PM
To: "Halicrafters" <Hallicrafters at mailman.qth.net>, <heathkit at yahoogroups.com>, "Boatanchors list" <boatanchors at mailman.qth.net>
Subject: [Boatanchors] Tuning a Boatanchor? 

I have spent the past 2 days trying to improve the tuning on my NC-109, 

If I use the standard method of tuning the inductor on the low end and the trimming capacitor on the high end I can make those points work. But he center of the dial will be off.

My interest is in the ham bands. Is there anything wrong with just tweaking the tuning to put he ham bands where they should be.

The National manual makes no mention of high side or low side injection? I is there a standard? I know some receivers use high side injection on all bands except the highest band. I think that is how I received this receiver.

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"
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