[ARC5] Request for help, aligning BC-453-B.

[Roy Morgan]

On Jan 28, 2015, at 11:59 AM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:

> On 28 Jan 2015 at 19:26, Leslie Smith wrote:
> 
>> SETTING THE MAIN DIAL.
>> The "pip" on the main dial was broken,...
> If the dial you have is NOT original to the receiver, you will have to go 
> through the exercise that someone else mentioned here by equalizing the 
> two ends of the dial with the cap fully meshed, then fully un-meshed. That 
> will get you close, and may even be almost perfect.
> ...
> Tuning may be "off" a bit more at the extreme ends, but not enough to worry 
> about.

Arc-5 folks,

I’ve long been interested in dial calibration and alignment.  Here is a trick I have used only occasionally, but it seems to work nicely (recently on a URM-25, for instance).  A frequency counter for signal generators or marker generator for receivers will help a lot.

Our goal is to have the dial as nearly accurate as we can get over the whole extent of the dial. If we adjust each end repeatedly till right on at each end, we may be able to do better. If, for instance the dial has error in mostly or all one direction through the middle, we can reduce the overall error.  Pick two points in from the dial ends about one quarter of the total span.  Adjust the trimmer and coil (usually) at each point for right-on calibration.  Now the error through the middle of the dial will be reduced and the error at the ends will be modest in the opposite direction.

To further refine this method, measure the errors at each end and the middle of the dial, and adjust the distance in from each end where the alignment is done to equalize the three errors.

If the error across the dial is positive for some part and negative for some part, I think that the next logical technique is to “knife” the variable capacitor slotted end plate.  I have never seen any description of how to do this - has anyone else?  The advice I’ve seen for the SP-600 receiver is: “Don’t try that!”  No doubt our well known manufacturers had test setups and tools for the task, and the production ladles with the skills to do it.

Uh oh.  My friend Google reveals one link of interest:

Dial Tracking, how good is good?
http://antiqueradios.com/forums/viewtopic.php?f=5&t=186857


Roy

Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958