My Avatar is a squared masked 16AP4 in an RCA, but it's nowhere near as square as that Hoffman, the sides and top on that are completely straight.

The loss of screen area is pretty dramatic when a nice straight sided 3:4 is masked off from a roundie. Double "D" shape is a good compromise.
Pix of 2 10 inch (10BP4) GE sets below:
jr

You can download them here: http://www.bobandersen.com/images/schematics/hoffman/

I couldn't scan them without breaking the binding so I took some digital pictures. I think they're quite legible, but let me know if you have any trouble reading them.

Very readable Thanks. If the chassis isn't too crowded I may try a few cap replacements.. I see all the wave forms there are they read between the show point and chassis ground?

Yes. This is a transformer set and the chassis is grounded.

I think Hoffman made their own tuners. It was unusual to see two 6J6's.

Check page 19 here for a Magnavox TV tuner with three 6J6's: http://www.earlytelevision.org/image...Sams-62-13.pdf .

I haven't seen the three 6J6 version yet, but I did work on a Magnavox recently with two 6J6's.

This is a really interesting comparison. Taken that both CRTs are the same size. Which one has the most square inches of screen exposed? The Double D looks biger to me but it might be that the cabinet color is lighter in color and for that reason the screen looks bigger.. and illusion.

The opening of the rectangular mask is 8-1/4 x 6-1/8 inches, the "double D" is 9-1/4 x 7 inches, so neglecting the loss of information in the corners of each display, a picture displayed on the "double D" masked CRT will be about an inch larger in each axis.
I calculate about 56.4 square inches for the "double D" and about 48 square inches for the rectangular mask (50.5 - about 2-3 sq in for the rounded corners). A "porthole" display of the same diameter (aprox. 9.25") would have a display area of 67.2 square inches. Of course, considerable information would be lost at the sides and corners.
jr