RCA model 9X571

check the speaker voice coil 3.2 Ohms?
Or voice coil lead shorting to speaker frame?.
green wire on speaker tied to chassis?
I know you said replaced all caps, but sometimes (leaky or open?) bad new one or reversed.
Capacitor c17 plate to tap on primary of the audio transformer?
Capacitor C16c 120 Mfd filter? 

mentioning PDF page file would help others to find a schematic. Not just Riders goofy page numbering system alone.

by the way, I have it as PDF page 1062/1737.

PS: output tube put on tube tester for shorts? tests

Boy, it's been so long since I worked on a radio, I may have forgotten how!

I have been cleaning out my junk shed, pitching stuff and just digging thru all the stuff.  I ran across this little 5 tube RCA that does not look so bad.  Certainly savable.   Chassis RC1079F, schematic found in Riders 20, page 18. I pulled the chassis, did the usual cleaning, recapped the entire set then fired it up on the Variac.  I instantly recognized the crashing sound as SMD.  Verification of positive voltage on the IF amp grid proved my suspicion.  I robbed an IF transformer from a known good parts radio (busted cabinet) and swapped it for the offending IF transformer.  The radio sorta worked, an alignment was the next task.  About half way thru the alignment, I lost audio, both in the speaker and on my VTVM.  I checked the signal generator, that seemed to be working okay, verified by my frequency counter.  I got out the signal tracer and found I had audio to the output tube plate, very weak audio on the wire going to the speaker.  I had voltage on the plate of the output tube and to the screen grid, which eliminated the primary of the output transformer of suspicion.  I'm either totally daft or I have a dead short between the primary and secondary of the output transformer.  How can that even be possible?  Why would I not have high voltage on the secondary if that was the case?  All I know is that I have audio and correct voltage on the plate of the output tube and little to no audio actually to the speaker.  There is nothing between the plate of the output tube and the speaker except the output transformer.  This is one of those goofy tapped primary jobs that RCA loved using.  What am I missing here?  I have never seen an output transformer exhibit this kind of symptom.  Typically, a transformer either works or it doesn't.  I usually find the primary open if I have a problem with one.  This one kinda works.