In article ,
"The Medway Handyman" writes:
Andrew Gabriel wrote:

It is common to wire two 2' 18W tubes in series, but you need
starters designed for series operation (actually, they are same
as the starters used for 120V mains). In your 3-lamp fittings,
you'll probably find one series pair and one standalone, and the
series pair will require different starters from the standalone.

These were 4' tubes, not sure of the wattage.

You can't run 4' tubes in series on a simple series ballast -- there's
not enough headroom between the sum of the tube voltages and mains voltage.
Some electronic ballasts do run multiple tubes in series, but they don't
use starters.

on, the unchanged tube still worked fine, but the other two flicked
on and off alternatively. You could see that one end of the tubes
was getting hot,

How could you see that?

One end looked red and felt hot.

Both ends should get exactly same heating. If one end glows
red and the other end white, then the red end of the tube has
run out of emission coating on the filament (usually ends up
coated around the tube end as black marks), and tube is dead.

I can't imagine what type of setup you are looking at, sorry.

--
Andrew Gabriel