I have a few questions concerning trigger start ballasts, how long do they last with an average one 1-3 switch ons and what do they do with eol tubes?

I have two from 1985, one buzzes however they both seem to be doing fine.

Trigger start really is a modified rapid start circuit.

When rapid start ballasts were released in the early 50s, all previously manufactured tubes had filaments designed for preheating. As rapid start ballasts only apply a few volts across the filaments, F40s in particular were slightly modified so that their filament could establish a discharge with that lower, continuous preheating voltage. Hence the mention "rapid start" often seen on 1950s and 1960s F40s.

Smaller tubes (i.e F20s and lower) never received such modifications, they remained "preheat". Things were made the other way around instead, the ballasts have been modified to accommodate the existing tubes. Trigger start ballast apply a slightly higher voltage than their "rapid start" counterparts across the filaments. Both types otherwise work exactly the same way.

I think tubes running on trigger start last a bit longer than on preheat, because the continuous preheat voltage applied, even when the discharge is established, can extract some more lifespan out of the electrodes. NPF ballasts can even run a tube with one bad electrode, which will only light on one half of the AC cycle, though the current limitation of the ballast isn't as efficient in that case, which leads to higher current in the ballast's coils and eventually it can overheat, especially if no thermal protection is present.

HPF ballasts are immune from this thanks to their power factor correction capacitor, which is usually located somewhere in series with the tube. Since capacitors block DC, a rectifying tube will charge the capcitor and current will drop to a point where the tube doesn't light much at all.

Thanks for the info, what will an eol tube do on lpf? (both of mine are lpf)

I should have mentioned that LPF and NPF are equivalent terms, my bad 

(Low Power Factor & Normal Power Factor, respectively, in case anyone wonders what they mean LOL).

So as I mentioned, EOL tubes will rectify on LPF/NPF ballasts. Not exactly good for said ballasts if left powered for extended periods of time. A few minutes is usually harmless though.

Oh, okay. I also found it interesting how f15t8's sometime have starting issues on them, specifically newer ones...

EOL tubes will rectify on LPF/NPF ballasts. Not exactly good for said ballasts if left powered for extended periods of time.

Depends on the ballast...
The 2xF40 ones actually run cooler with an EOL lamp, even running for hours at a time. (they don't get a whole lot of use, but have 4 2xF40 LPF shoplights in the garage...all with EOL lamps & they've been that way for years(some over a decade) & still work fine .lol. .lol. )


The 1xF20 ones will overheat with an EOL lamp. (while 2xF20 like 2xF40 are fine)

The HPF Trigger Start ballasts can also be rather violent in terms of EOL, specifically the single lamp versions... depending on the ballast.
I've found that out the hard way on several occasions.