On Saturday, 21 April 2018 07:35:03 UTC+10, T i m wrote:
On Fri, 20 Apr 2018 21:55:35 +0100, ARW
wrote:

snip

The
starter is a one shot process.

Agreed, it *should* be but I was wondering under what criteria it
might try to kick in again after say a couple of hours? eg, what if a
ballast was going or a tube etc (except the ballasts have been there
since I fitted the units possibly 30 years ago (could be less [1]) and
they currently have new Philips tubes).

Once the tube is lit it has no further use.

Agreed.

snip

Voltage drop to the house?

Well, that's the sort of thing I am open to but if I understand it
right, the ballast and tube are in series across the mains (forming a
potential divider) and the starter is in parallel with the tube on the
other side of the filaments. The starter is a voltage / current
sensitive device so it *could* be falsely triggered if 1) the voltage
goes above it's trigger voltage [1] and / or 2) the starter is made
such that it's over sensitive (to voltage)?

I know the bottom line is that the electronic (and old Philips
70-125W) starters work, just that the new 4-80W ones don't (or not
fully).

Would you use / have you successfully used 4-80W starters on 70W tubes
do you know / remember please Adam?

I think I'll try to pick up some branded (Philips?) 4-80W starters and
see if they work reliably in my lamps.

Cheers, T i m

[1] Where the gas (Argon / Neon) in the starter switch capsule get's
hot enough to heat the bi-metallic switch and close the contacts.

I would suspect things around choke. Clean and reconnect the terminals. Sometimes cobweb or cockroach muck could cause change in voltage across the choke. As a total unit, once the plasma is struck the total energy is sum of choke drop and the plasma drop. Plasma energy is generally low, hence choke is the component taking most enrgy. Choke may develope intermittency due to failing insulation.failing insulation.