At this point, I have definitely noticed a difference in some of my ballasts' behavior. One good example. Yesterday, I put in a worn out, but known working Universal 446-LR-TC-P in my bronze Sylvania shoplight. I put in new/broken in Sylvania F40/CWX lamps, and the lamps would flicker, but not strike. I then put in vintage Sylvania F40/CW's, and they fired right up. Then, I put the F40/CWX's back in and wait. About 15 seconds later, the lamps struck, but they were flickery and the ballast was quite a bit louder.

It seems that Ecoluxes, newer black etch Sylvanias, and Altos are much harder to start. I have also noticed that ballasts are much louder. I think that modern 40 watt lamps have been altered so that they slowly burn up old ballasts, causing them to fail and be replaced. Sounds possible what with all the other BS going on.  What do y'all think?

I hate to think that manufacturers would actually make lamps that intentionally kill off ballasts, but they have every reason to do it. I have a hunch that at least part of the reason for the "energy saver" lamps was to do exactly that. Do you have a Kill-a-Watt? If so, I'd be interested to see if the electrical characteristics of your ballast change based on the lamps it's running. I have one, so I'll have to try this experiment when I get the chance.

Once, I tried replacing some mercury-starved F34 Altos in a fixture at school with new F40/CWS Altos. The new lamps wouldn't strike, so I figured there must be a problem with the ballast. I put the old F34s back and called it a day. Later, just for the heck of it, I tried installing some 2013 Canadian Sylvania F40/CWX lamps in the same fixture, and not only did they strike, but the fixture hasn't had a problem since. I never tested the CWS Altos in another fixture, so I'm not sure if they were defective or not. To date, all the other newer T12s I've used have worked fine.

I would rather guess for the new lamps either being deffective or not being settled yet.
The lamp just need the burn-in time (some 10's of hours, preferably as few starts as possible) to work properly.
The old lamps already get such treatment and the deffective ones were trashed long in the past...

Not a bad idea, really. You could run the CWXs for 2 days straight, let them cool down, and try to fire them up on the Universal again.

I measured a variety of different lamps on my 1973 shoplight equipped with the "original" 1973 GE Bonus Line ballast.   

You've got nothing to worry about. Your numbers show it all - there's no difference between old and new lamps that has any negative effect on the ballast. Check cathode continuity of the lamps that are hard to strike or flickering.

Let's keep in mind too, you are also talking about old ballasts..  I'm removing F40T12 Universal & Advance brand ballasts right now that were put in back in 1973.  Most of them still working just fine, but there have been a few failures over the years... what caused them?  Who knows.  Some simply got old and hot enough that they started leaking.  Others just flat out failed and I never bothered to cut them open to find out why.  But this much I do know.. there are more older Universal Ballasts that have survived then the Advance brand   The old GEs were the worse!  Leak leak leak!  So many ballast cover plates that had those installed in those fixtures have tar/oil dried up from when they failed.  Yuck! GEs like to fail by spewing out the oil/tar.  Advance seems to like to just burn up and give a big smelly smoke show.  Universal?  Well they just generally quit without any big fuss.  Usually one or both tubes will glow but not ignight. 

@RyanF40T12, are you replacing them with something?

Some older ballasts do not like 34W lamps and overheat the ballast.

The T12 ballasts that I am taking out are being replaced with T8 Sylvania ballasts and lamps.  And you are right, the old ballasts do not like the 34 watt lamps.  I am confident that a few of the fixtures ran 34 watt lamps for a time as I had put in a bunch of 34 watt tubes into a few of them back before I knew any better, 15+ years ago     Clearly states on the ballast, for use with 2 40 watt lamps.  The ones that were approved to work on 34 watters indicated so.  I definitely burned up a few of the single lamp hallway fixtures equipped with the Advanced ballasts for 40 watt tubes only after a few years of running them on 34 watt tubes.  Ah well. 

I have noticed yet another phenomenon with modern fluorescent lamps, especially Sylvania lamps. I think they are getting shorter! A while back, I purchased a pair of Sylvania F40/Daylight Full Spectrum lamps at K-Mart, and because they are so short, they are unusable in my 1973 Shoplight, and my 1950's bronze finish shoplight. (See my gallery.) The Sylvania F40/CWX lamps, I've been using in my 1973 shoplight fit slightly better, but you have to push the lampholders towards each other for the lamps not to fall out. I tried my vintage Westinghouse F40/CW and 1964 Sylvania F40/CW in my 1973 shoplight tonight, and they both fit perfectly with no gap. Has anybody else noticed this?

The modern Sylvanias fit like that on both ends, and the Westinghouse could not fit any more snugly!

I'm pretty sure I've noticed this, as well. I know my 34 watt Sylvania leaves considerable gap at the lampholders. I'll have to haul out my Mainlighter and check that next time I'm home.

It's been very prominent in the GEs as well.  As I replace EOL 1989 vintage GE F40T12s they can be somewhat difficult to get out of the sockets and fixtures.  May times, they crack the sockets while I take them out because they seem to be too long for the fixtures that they went into.  I haven't noticed that big of a difference with Sylvania tubes and they seem to fit just right into the fixtures that the old GEs came out of. 

Can you measure the length with a tape measure(using one that lets you hook on the edge for consistency)to the exact millimeter? I am curious how much difference you'll actually see. I noticed that some lamps leads sticking out a bit from the pins and the sharp ends snag on the back of the sockets.

The newer sylvanias aren't that bad, they run perfectly on my preheat NPF ballast. The ones to watch out for are GE. Those sometimes are known for random vacuum loss and filament failure.