I luckily found some Aura Twin Strike, still looking for 'Mini Strike'.

Aura is known for their superior quality, I have some T8 tubes in T12 housings aswell. Might upload some pictures later.

I also like Palmstep, the 'Frigostart' series have a very long preheat time, like 4 seconds or so.
The 'Turbio' series act like the old Osram Deos (St171) with a built-in diode, halfwave preheat current and ignition within 0.3 seconds.
Their most sold product is the 'Ökostart' (Ecostart) with a moderate preheat time, enough for most post-80s T12 and T8 tubes.

I'm not concerned about the temperature of the cathodes because the 3.4V are applied when tube is running, so the ion impact adds to the filament heating.
In total, the filament receives enough thermal energy to keep the emitter up and running.

When not lit yet, the voltage is 6V which is good enough to heat the cathodes properly. I've attached a picture of my ATLAS 20W preheat tube on a 6V
heating transformer, you can see that the filament has enough temperature. The other tubes (40W, 65W) are in the same ball park.

The 9V electrodes are constant current type electrodes, they develop a drop of around 9V when run on a conventional ballast in preheat mode (short circuit
current). They are designed to reach emitting temperature when the preheat current is passed through them. The voltage across the filament depends on age
and state of the electrode. The voltage drop of 9V is valid for new filaments with the full emitter available, they tyically develop a voltage drop around
8 to 11 volts, that's why they are classified as '9V' electrodes. Wornout cathodes have a much higher voltage drop, I measured up to 14 volts on T12 and
up to 17 volts on completely blackened T8 lamps. CC electrodes can cross-ionize, drastically reducing their resistance, but that is not a problem when run
on a magnetic ballast.

Rapid start electrodes are constant voltage electrodes, they are designed to reach emitting temperature on 3.6-4 volts. The current through the filament
develops depending on age and state of the cathode. CV electrodes do never cross-ionize, as this had fatal consequences if the voltage source is not
current-limited. However, most heating transformers do not have the best magnetic coupling, so the output current is somehow limited.

If you put a rapid start tube into a preheat fixture, the short circuit current of the magnetic ballast is not high enough to heat the low resistance
filaments up to the correct temperature, so switch start fixtures would have a hard time igniting RS tubes.
Vice versa, if you put a preheat tube into a rapid start fixture, the preheat voltage is not high enough to bring the 9V electrodes up to temperature.

In both cases, the cathodes would run too cold, probably blackening the ends of the tube and paying with service life hours. Besides that, nothing else
would happen.

Actually no, there are 3 seperate type of T12 flourcent tube

those with 8V cathodes are *not* as you describe, they are designed for 8V-10V cathode heating, usually by way of an Autotransformer Quickstart unit after the choke, but also can be applied by way of non-autotransformer cathode heating unit (see US Trigger-start ballasts and British Dimming ballasts)




the current defined type your thinking of are their own standard in itself, and they have no defined cathode voltage or resistance


here is an excerpt from one of my recent comments on the Gallery



TL lamps are switch-start lamps with current-defined preheating electrodes that have no actual set voltage, an MCFE tube will *always* have 8V high resistance cathodes

but a TL lamp will have cathodes of no actual fixed resistance/voltage value, for example a 1980's Dutch made TL 20W/05 Ultraviolet tube I have has cathodes that are somewhat of a medium resistance, but the dutch made MCFE 20W/840 tubes I have are proper 9V high resistance cathodes


a TL lamp is only an 8V lamp if its a TLA type *or* there is a T suffix *after* the colour code, ie TL20W/33T, but I have never actually seen the latter pictured, only mentioned in some catalogs

see page 346 if going by PDF counter or Page 310 by the page number on the catalog itself, for more details

https://www.lamptech.co.uk/Documents/Catalogues/Philips%20-%20Catalogue%20-%201979%20UK.pdf



this is why for a lot of common T12 tube types, there are actually 3 separate types listed in the IEC standards document


for example for the Humble 40W 4ft T12 tube, there exists 3 official standards/versions



FD-40-E-G13-38/1200

60081-IEC-2440

which is a Switch-start/external starter tube


FD-40-L/P/H-G13-38/1200

60081-IEC-4440

which is a 8V High resistance Cathode tube


FD-40-L/P/L-G13-38/1200

60081-IEC-5440

which is a 3.6V low resistance cathode tube



the "FD-40" string is the ILCOS code for each type and the 60081 is the IEC data sheet number for each type for anyone else who wants to sleuthing




it is generally accepted that a switch-start tube will have High resistance cathodes, (if you look at "both cathodes in series" resistance value under the info for ballast design heading in the IEC 60081) but that is not always the case nor is cathode resistance/voltage actually controlled or defined for those tubes


cathode voltage and cathode resistance is only explicitly controlled/defined for the 8V and 3.6V tubes

Awesome, I have some Aura Thermo tubes aswell. Both 36W form, and in 58W! I have a whole box of aura QuickStrike, hehe.

Lovely to hear that I'm not the only Aura fan here! Yes, their tubes are amazing. 100K hours with ease. I love them! I've got a collection of Aura Ultimate Thermo, and standard Aura Ultimate tubes they're going to outlast me! And yes, there are many versions of electronic starters which all do their job really well!

cathode voltage and cathode resistance is only explicitly controlled/defined for the 8V and 3.6V tubes

So was it a coincidence that I always measured in the area of 9V across the cathodes in new switch start tubes?

I don't have an autotransformer ballast with built in heater windings, so I have never measured these.
But if there's 3.6V, 8V and high resistance electrodes, what's the use of the 6V transformer then?
I mean, I also have 4V transformers from a set of dimmable fixtures with rapid start tubes, I only used the
6V transformer when dimming standard tubes.

And the PDF says, MCFE tubes have 10V electrodes, am I getting something wrong here?

Back to the topic of why apparently heating the cathodes without the discharge causes visible evaporation, but doing the same with discharge present at the same voltage causes no evaporation. I said there is no feasible physical explanation. But recently I re-read a 1971 book of J.F.Waymouth "Electric discharge lamps", where John actually notices cathode filaments going cooler with the discharge. Unexpectedly, an explanation is cooling by electrons. As electrons are leaving the cathode, they have to travel an energy barrier of 1-2eV and so the electron flow is taking some power of around 0.5-1W from the filament!

@RRK Thanks a lot, this is very interesting!

I have heard of electron cooling in connection with some types of vacuum tubes, where you have to add power to the heater above a
certain power level. But I have never considered this in fluorescent lamps. Some years ago I have noticed that MV lamps turn black
more quickly at the electrodes when they are operated at too low a power. Could this be the same effect?

So was it a coincidence that I always measured in the area of 9V across the cathodes in new switch start tubes?

I don't have an autotransformer ballast with built in heater windings, so I have never measured these.
But if there's 3.6V, 8V and high resistance electrodes, what's the use of the 6V transformer then?
I mean, I also have 4V transformers from a set of dimmable fixtures with rapid start tubes, I only used the
6V transformer when dimming standard tubes.

And the PDF says, MCFE tubes have 10V electrodes, am I getting something wrong here?

as I mentioned in my previous post, most current-defined switch-start tubes are generally made to be a high resistance tube, but also what current are you measuring the 9V at? if its the short circuit current of the 40W choke, then thats too high, thats only designed for momentary preheating, not continuous preheating, I would adjust mains input voltage on the Variac until your at about 400mA at the cathode (for a F40T12) and then see what the voltage drop across the cathode is


also the transformer you show is 6.5V (not 6V) 6.5V is the minimum allowed voltage for an 8V High resistance tube, I have attached excerpts from IEC 60081 of the Switch-start specification of F40T12 and the High resistance 8V cathode specification of F40T12


note how "Both cathodes in series for ballast design" for the switch start tube is 40 Ohms ie 20 ohms per cathode, the same as that of a high resistance 8V tube *but* note that no explicit cathode resistance or voltage is defined


you can see this non-definition in action on the F36T8 datasheets where earlier versions dont define a cathode resistance, but later ones do for HF ballast reasons, and you will note that the "both cathodes in series" does not match, same with the 28W 2D lamp, which was originally designed as a low resistance cathode rapid start lamp, but later IEC standards have it as a high resistance cathode tube despite both cathodes in series still stating 18 ohms, I have always been a bit grumpy with the IEC over that, because it breaks compatibility with rapid-start 2D fixtures, but I digress


another example is the 60W Circline which has both cathodes in resistance defined as 25 ohms (12.5 ohms a cathode) but an example I measured is 6 ohms per cathode, see my write up and comments under this upload

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-258704


its quite common for high resistance cathode tubes to be called "9V" tubes in the US, or "10V" tubes in the UK, but the official IEC test voltage is 8V

I highly recommend reading this booklet for details on what i mean by "Quickstart autotransformer" as I am not referring to an auto-transformer ballast, but a seperate Autotransformer for cathode heating that is placed after the choke, this is mainly a British practice


https://allthingslighting.co.uk/albums/userpics/10002/Atlas_Technical_Pocket_Book_1966-7_Pt1.pdf

@RRK Thanks a lot, this is very interesting!

I have heard of electron cooling in connection with some types of vacuum tubes, where you have to add power to the heater above a
certain power level. But I have never considered this in fluorescent lamps. Some years ago I have noticed that MV lamps turn black
more quickly at the electrodes when they are operated at too low a power. Could this be the same effect?

IMO, unlikely for HPM. For dimmed fluorescents, you have constant extra heating applied to the electrodes, no such luxury for HPM. So, the heat applied to the electrodes just reduces proportionally to in-between of 1-st and second order of lamp current. At some point, electrodes become too cold to keep enough electron emission and cathode drop starts to increase, increasing ion speed and cathode sputtering. Also, at some point of current reduction the arc will probably migrate to the starting coil parts of the electrodes back from the tips, increasing sputtering too.