I noticed a dimensional problem with the 6E5 that was installed in the '38 Zenith 15 tube chassis. The end of the tube doesn't go all the way to the dial plate. It's short by about 3/8". I compared it to a dud 6T5 and the 6T5 fits properly. i looked at a couple other 6u5 and 6E5. Some are longer, some are shorter. Wasn't there a spec for overall length? The 6T5 tube holder/mount fits over the tube base, not the socket so a longer tube has to be used.

GE gives the same outline drawing for the 6E5, 6T5, and 6U5:



Bob

That +- 3/16" is the problem. I found the Tung-Sol spec and it's MAX is 3 7/16". I found another dud 6T5 and it's short.

I reality, I think the problem is the Zenith design. I know it doesn't help the OP's problem, but a good design would have taken the height variation into account. OTOH, maybe it was done that way on purpose with Zenith-branded tubes being specified at the maximum length in an effort to force their use as replacements ...
John

Yes to the first part, a Zenith design quirk. No to the second part. I have 2 Zenith-branded 6T5 tubes, 1 short, 1 long.

That makes me about as correct on average as the weatherman. Do I get to keep my job, too?
John

Remember that length does not equate to performance