6BK4 versus 6BK4C/6EL4A
 

Hello-

Can anyone here tell me if a 6BK4C/6EL4A is a safe substitute for the older, plain 6BK4, in an older 21" color set? Thanks.

I may have answered my own question. NJ7P has a site with specs for both tubes:

6BK4
http://www.nj7p.org/Tube4.php?tube=6BK4

6BK4C
http://www.nj7p.org/Tube4.php?tube=6BK4C

The "C" seems to be almost identical except for a couple of higher voltage and current specs, probably what I should expect for a newer version of the same number.

It was always explained to me that the newer 6BK4C/6EL4A had better radiation protection than the older 6BK4 tubes. More or less a newer and improved version of the original's.
-Tony

Back in the day I was told it was better to replace the older 6bk4 with the newer 6bk4c/6el4a for better xray protection. So I'd play it safe to use the newer tube myself can't hurt.

Thank you for the replies. The set I am working on does not have its shunt regulator in a cage, so the better protection is definitely worthwhile.

the late 60's Zenith tv chassis service manuals will suggest that any tv using the shunt regulator tube brought in for service using the 6BK4 be inspected replaced with the new and improved 6BK4C or 6EL4 for better x-ray protection.
There is more lead in the 6bk4c and 6el4. You can feel the difference in weight when comparing the the standard 6BK4 or 6BK4B.

I also thought that the 6BK4c had an improved element design that prevented filament sag if the tube was in a horizontal position?

Perhaps that was some other regulator i was thinking about?

They are "shunt regulators" which means they are like a clamping diode. All 6BK4 and 6EL4 will all work interchangeable. They were all updated because the earlier ones emitted X-Rays.