On Mar 25, 6:25*am, Fred Cameron wrote:
Would 3-400's be exact replacementsfor the 3-500's *in my L4B?

Sometime in the 60's, Eimac stopped selling 3-400's and instead sold
the "upgraded" 3-500's as drop-in substitutes with higher dissipation.

I don't believe that 3-400Z's have been sold since the early 70's...
of course someone might have them sitting on the shelf.

Most of the electrical parameters are similar between the -400 and
-500 but of course the -500 has more dissipation. The intended path
was that folks would put 3-500's in place of 3-400's - there were some
slight physical changes and I think the 3-500's are supposed to use
beefier anode clips etc but many amps using 3-400's just had 3-500's
put in with no changes. I think the L4B originally had 3-400Z's.

Tim.