06-03-2018, 10:57 AM
June 3.
Alignment time! All five bands, as well as the Magnetic Tuning, are now aligned.
It's been several years since I worked on one of these 1938 Code 125 RF units, and I had forgotten the fact that while the adjustments are relatively few compared to the 1937 RF units (and the 1938 Code 121 models), this also means that it is usually not possible to achieve perfect tracking on all bands.
This is indeed the case with this 38-690. 580 kc is coming in just above 590; 1550, at 1530; 990, at 1005; and 660, at 675. It's the best I can do given the limitations of the adjustments and age of components - remember, this radio is 80 years old and I did not replace any mica capacitors in this RF unit (not that that would have made much of a difference).
Here's a demo showing that the radio is working on all five bands. I basically skipped over bands 3 and 4 but you can hear the typical noise on these, proving that these bands are not "dead".
[Video: https://youtu.be/2Uo65-rhGuU]
It still produces a slight static or "sizzle" noise at first power on which sounds like it is coming from the RF unit, but it now stops almost immediately. I'll probably clean the band switch one more time - I did hit it with an evaporating contact cleaner yesteday, followed by compressed air in a can last night. Nevertheless, I consider this project finished. After 3+ months, I am not inclined to go any further with this one.
So that is it for this thread. Many thanks to Sam and Mike Schwartzman for the assists (tube shields, knobs, and the third and final RF unit, respectively), to those who posted words of encouragement along the way, and to all of you for reading along.
Alignment time! All five bands, as well as the Magnetic Tuning, are now aligned.
It's been several years since I worked on one of these 1938 Code 125 RF units, and I had forgotten the fact that while the adjustments are relatively few compared to the 1937 RF units (and the 1938 Code 121 models), this also means that it is usually not possible to achieve perfect tracking on all bands.
This is indeed the case with this 38-690. 580 kc is coming in just above 590; 1550, at 1530; 990, at 1005; and 660, at 675. It's the best I can do given the limitations of the adjustments and age of components - remember, this radio is 80 years old and I did not replace any mica capacitors in this RF unit (not that that would have made much of a difference).
Here's a demo showing that the radio is working on all five bands. I basically skipped over bands 3 and 4 but you can hear the typical noise on these, proving that these bands are not "dead".
[Video: https://youtu.be/2Uo65-rhGuU]
It still produces a slight static or "sizzle" noise at first power on which sounds like it is coming from the RF unit, but it now stops almost immediately. I'll probably clean the band switch one more time - I did hit it with an evaporating contact cleaner yesteday, followed by compressed air in a can last night. Nevertheless, I consider this project finished. After 3+ months, I am not inclined to go any further with this one.
So that is it for this thread. Many thanks to Sam and Mike Schwartzman for the assists (tube shields, knobs, and the third and final RF unit, respectively), to those who posted words of encouragement along the way, and to all of you for reading along.
--
Ron Ramirez
Ferdinand IN
