Open heaters seemed to happen most often on the series string AC/DC radios. Either the 35Z5/35W4 or the 50L6/50C5 would open up.

I have not seen many on TVs.

Ditto here. I had a 35Z5 open up on me this past weekend but I cannot remember the last time I found a dead filament tube in a TV, save for some HV tubes where the glass had cracked.

I had a Zenith 23" b/w set where the filament was open on the crt. Hooked the crt filament leads up to a horiz output tube and the tube lit up, so CRT was definitely bad. There were some other cases of no CRT filament I have seen but it was due to the crt being slightly cracked in a non-obvious area and losing its vacuum.
Also had a 6MJ6 horiz output tube burn out filament on a very well used CTC-39.

Frenchy. Are you sure the device is wired into the secondary somewhere? Looked up the original schematic that came with the CTC10 and couldn't find it. Found the CTC10 RCA service literature and ditto, but I could have missed it.

Had to replace the Thyrite in that set in the latter sixties and I'm pretty sure it went in the primary of the power transformer. The fils are definitely in the loop because as I mentioned somewhere earlier, it takes the pilot lamp two seconds to ramp up to full brightness.

Pete

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Took another look at the service lit and...
 

found the surge device this time. In the CTC10 at least, the 'Thyrite' is R136 and it's in series with the power transformer primary. Listed as 'Surge resistor, 79 ohms cold' part number 107291. A secondary benefit with this design is that room lights on the same circuit don't dim at turn-on!

bgadow mentions having the '60 Motorola with the B+ delay switch. My '59 Motorola 21" has this same switch. I think my late-50's RCA portable has one as well. The switch engages about 30 seconds after turning the set on. This delay switch apparently works well with the electrolytics since both of my sets still have all the original capacitors in them and play just fine.

You are right, I was going on my bad memory, R136 in the primary on my schems, so it would indeed ease the power-on thru the entire set.