hi all , could anyone tell me what the difference between the 3a3 and the 3cu3a rectifier tube is. could the 3a3 be used in place of the 3cu3a without any problems or limitations to the hv. i am using it now but i cant find that number to replace the 3a3.

3CU3 draws a bit more filament current (280 mA vs 220). It also has a bare filament, as opposed to the 3A3 which uses an indirectly heated cathode.

Close enough for testing, but I would suggest getting the right tube. TV high voltage tubes are in limited demand, and generally sell at dirt cheap prices.

3CU3 draws a bit more filament current (280 mA vs 220). It also has a bare filament, as opposed to the 3A3 which uses an indirectly heated cathode.

Close enough for testing, but I would suggest getting the right tube. TV high voltage tubes are in limited demand, and generally sell at dirt cheap prices.

ok so if the set calls for 3a3 i should not use the 3cu3a. ill have to look because my 64 rca had the 3cu3a in it but i replaced it with the 3a3 so ill see the tube layout if its even there dont remember.

Timmy,

On RCA color sets like the CTC16 up through the CTC 39, HV rectifier tube length is an issue.
Generally, a plain old 3A3 is longer than a 3A3B or 3A3C and replacing it should consider if it seats fully into the flyback's navel.

Dave

There is one more thing I remember about the HV rect in my first round-tube set, a RCA Danish Modern CTC16XL, a "most glorious tv" I got when I was 15.

This TV had a rebuilt Channel Master 21FJP22, had no red emission and NO horizontal sync, just the picture scrolling horizontally with the control near the center. Of course I was fumbling around in the oscillator and afc stage area. Out of desperation, I started replacing tubes elsewhere; 6JE6, 6KA8, 6DW4, 6BK4, 2AV2......THEN I found a 3CU3 in the HV cage and, when I replaced it with a 3A3, the horizontal locked solid. I borrowed the CRT tester from the HS shop, brought the red back, and transported it there learned how to do a marathon purity and covergence session that lasted a week. The picture on this RCA looked as good as the 1971 Zenith downstairs!

Years later, a former RCA factory-service tech confided to me they found alot of sets this way (after other attempts failed or even introduced this new problem) because everyone wanted to stock the fewest HV rect tubes in thier caddys, and a 3A3 was an old-school type that was "improved" in the 3A3C and some others.

i have two sets, rca new vista with the ctc16x and a magnavox 16 clone that has the hv cover with the rec tube that closes in on the fly. i have to check them just to make sure they are correct ones in there. the sets play fine but ill look anyway, and thanks for that info.