A quick check shows the crt filament open. I have a feeling the 17QP4 crt went to air. Set had a complete recap and was restored to working order in 2000.
Cabinet is customized to fit into a specific place in his house, owner likes the set and would really like it in working order.

What are the odds of finding a 17QP4 or a sub?

http://justsmog.com/Clay/721.jpg
http://justsmog.com/Clay/722.jpg
http://justsmog.com/Clay/723.jpg

this is not looking good for a sub on the crt

http://antiqueradios.com/forums/viewtopic.php?t=142680&view=previous&sid=8e14797ecf0108e424ffae9a36e3cd43

With the base being what it is have you tried to resolder the pins?

How about this one, the price is waay high but he is taking offers.

http://cgi.ebay.com/Vintage-RCA-Victor-TV-PICTURE-TUBE-Model-7-T-122-/140494214644?pt=LH_DefaultDomain_0&hash=item20b61b95f4

17QP4 is a glass CRT, that one is metal.

Maybe that one is a 17CP4?

17QP4 is a glass CRT, that one is metal.

Maybe that one is a 17CP4?

The one in the set im working on is metal?? Maybe the crt in this set is a sub, Im getting the number off the sams.

That looks exactly like it but $255! the odds of return would be better buying lottery tickets!

Aren't these noted for leakage?

My Riders shows that either a 17QP4 or a 17CP4 is used in this model. Not mechanical ly interchangable.

Is the cracked plug loose to the touch. Many of them are, and the leads going into the pins are often worked loose. If the filament is open there is no glow inside the neck. Apply current to the crt via a tester or if you can power the set up and move the plug around with your hand. If my guess is right you will hit the sweet spot and you will see the filament light up. If it does, the crt may be just fine! Normally the filament is not going to be open before the crt is found to have low emission, shorts, or gas and would have been changed out. If there was no brightener connected, then the tube was more than likely OK when the set was last used.

Make sure the TV-PH. switch is in the TV position, or the CRT won't get any heater voltage.

Was using a tester then an ohm meter. Am going to look at the socket and maybe remove it to inspect the wires.