[HomeBrew] Magic Eye/S-20R musings

[kwylow zinjanthropus]

All you BA enthusiasts out there:

I just helped a good friend of mine, Bernie, another ham BA enthusiast,  construct a magic eye (1629) based tuning indicator for his S20R. You can find this project at http://antiqueradio.org/magiceye.htm

Just ensure that when you start the project, you have ALL the parts. Unfortunately, we didn't have everything that we should have and the project was delayed by another couple of hour trying to located two 10 meg resistors and anothe 1 meg we forgot to get during the parts run.

One of the interesting parts about this project was the use of the voltage doubler to get the 1629 magic eye tube to work. 6.3VAC doesn't cut it for this tube (which is a variation of the 6E5/6U5). It is a 12.6 fil jobbie that was used (I think) in military equipment. 

The initial construction (which began around  an octal socket) was intented to be a little organized but by the time I was done, I ended up "dead bug construction" placement of many of the last components. But, she worked beautifully (after I had to troubleshoot the reason why we couldn't get filament voltage from a loose wire!). 

We didn't have a five pin plug or tube to bust up so I ended up plugging in the wires as is. So, as long as it works, that' s o.k. Per the article, we had to tap the AVC line. The best spot to do this (and double check a tube book and schematic) was to take pin 5 of the 6H6 socket and solder in a wire and trace that to the unused pin at pin 3. 

FWIW for a nice weekend homebrew project,

Cal, N6KYR



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