According to Houze; Whelens 52 was one of the prototypes made before actual production in 1934. Whelen wrote a review in 1933, according to the serial list on 52s 26669 was January 32. How accurate the serial list is is anyones guess and the receiver could have been in stock during that time as they probably made in batches.

I learn something every day, and a lot of times it's that what I learned the day before was wrong