Westinghouse wh22t

I first bought a Westinghouse WD-20 in pretty bad shape. Then I ran accross this WH-22T in fair condition and still running, so I bought it just to save me all the restoration hastle. What I would like to find out is how old this box is. I am also curious as to which box is the oldest. The serial no. on the WH-22T is 20501614 and the part no. is Y-37048.
I am interested in selling the WD-20. '>

[Jim]

The WD-20 went into production before the WH-22t, but I'm not sure if the production dates overlapped...  I know the WD-20 was made for several years and may have been still available when the WH-22t went into production; but I'm not exactly sure on this...