35w/55w SOX (35w SOX runs at 70v 0.6a and 55w SOX runs at 100v 0.6a)

35/39w M130 PSMH ballast (35/39w M130 PSMH runs at 85v 0.6a)

90w SOX (90w SOX runs at 125v 0.9a)

70w M98 PSMH ballast (70w M98 PSMH runs at 90v 1.0a)

135/180w SOX (135/180w SOX runs at 164v 0.9a)

100w M90 PSMH ballast? (100w M90 PSMH runs at 100v 1.2a)

Should 135w and 180w SOX lamps be okay if they are supplied with a 100v output voltage and be allowed to draw 1.2a?

Does anyone approve of my list of affordable magnetic ballast alternatives for running SOX lamps in the USA?

Should 135w and 180w SOX lamps be okay if they are supplied with a 100v output voltage and be allowed to draw 1.2a?

I think you are missing the major difference of how any discharge works regarding its supply , vs e.g. incandescent. In other words difference between voltage source and current source.
Voltage source is a source of electrical power, which (in its operating range) dictates what voltage would be across the load and it is the load property, what current will flow. If the load current changes, the source voltage remains constant. So because the voltage is constant, increasing the current, so decreasing the load resistance is what yields higher power.

With current source it is exactly the opposite: The source side dictates what currents has to flow, it is then the load, which dictates the voltage by its voltage drop. If the load changes, the current still remains the same, so the load has to change its voltagedrop.

Incandescent is a resistor, so it does not matter if they are fed from a current or voltage source.
But the discharges are things enforcing their voltage drop. So So it has to be operated from a current source - a device feeding certain current and letting the load (the discharge) dictate what the voltage will be.
But the discharge is not always conductive, it needs the voltage to first go high enough to ignite the discharge. Ideal current source will do so (it is for it something like an inrush current for a voltage source), but a real current source has its limits, mainly what is called OCV. It is the hypothetical maximum load voltage the current source is able to support (in fact when reaching OCV, the current already drops to zero). So because discharges need an elevated voltage for any (re)ignition, they need certain margin between their operating voltage and the source OCV.

The voltage is dictated by the lamp construction, so if 180W are 164V lamps, they will drop 164V regardless of the current. If the source is not able to deliver this voltage with sufficient margin, the system will just not work, the arc will extinguish or not ignite at all.

What matters if the ballast will be able to maintain the arc is, whether the ballast has high enough open circuit voltage to restrike the arc after each zero crossing. Ballpark figures use to be for the OCV to be at least twice the arc voltage. So a 164V arc lamp needs ballast with at least 330V.
But to be more complex, this condition has to be met at all stages, so include when the electrodes are still cold. With high pressure lamps this uses to be not that much problem, because the anode column uses to have low drop, making up room for the extra electrode drop, so for a 100V lamp a ballast with about 230..270V OCV uses to be sufficient.
But with SOX the pressure is low all the time, so is the anode column voltage drop, so the extra voltage drop on the cold cathodes needs to be handled by the ballast as the extra arc voltage. And it uses to be about 80..100V, so from a 164V nominal you get about 230..260V arc, which requires about 500V OCV.

So the ballast wont be able to feed the current high enough to warmup the electrodes so to sucessfully start the lamp.


And for the current: The lamp will swallow whatever current you will feed in and still maintain the arc voltage. But that does not mean it will survive it or work properly with the current you are feeding it.

Are my alternatives for 35-90w sox lamps reasonable?

Are my alternatives for 35-90w sox lamps reasonable?

I know the 18W, 35W and 55W are used with just a series choke and the SOX electronic ignitor on 230V, so the MH ballasts of the apropriate current and the SOX ignitor then should work. Of course, the original MH ignitor should be disconnected, it may blow the SOX one.
But I'm nor sure the 35W MH is really 0.6A, I do remember it as a 0.5A lamp, so I may be wrong.
So check the arc current with an A-meter (the lower current should not harm the SOX, it will just not make it perform).
0.6A are the MV 50W, but these would be hard to find these days (when MV only ballasts are banned for already quite a few years in the US and tge 50W does not have its probe MH counterpart).

The ballast choices can be extended quite much if you can use parallel or series ballast combinations. For 120V, you may also look into voltage step up to arbitrary voltages using transformers or high power HX ballasts, and then ballasting off that voltage

Just to let you know @Medved, I often use lamp data from sailormoon_01_uk to determine HID lamp current characteristics.

I know the 18W, 35W and 55W are used with just a series choke and the SOX electronic ignitor on 230V, so the MH ballasts of the apropriate current and the SOX ignitor then should work. Of course, the original MH ignitor should be disconnected, it may blow the SOX one.
But I'm nor sure the 35W MH is really 0.6A, I do remember it as a 0.5A lamp, so I may be wrong.
So check the arc current with an A-meter (the lower current should not harm the SOX, it will just not make it perform).
0.6A are the MV 50W, but these would be hard to find these days (when MV only ballasts are banned for already quite a few years in the US and tge 50W does not have its probe MH counterpart).

Will regular US 4kV PSMH ignitors instantly pop SOX electrodes and render SOX lamps unusable?

Will regular US 4kV PSMH ignitors instantly pop SOX electrodes and render SOX lamps unusable?

No, why should they?
Stop looking at them as a 4kV voltage sources. They are current sources, the "4kV" means they are capable to reach up to 4kV into the open circuit.
But normally the load (lamp) imposes lower voltage, so the voltage will not reach the 4kV at all.

But the MH ignitor may not be enough to start the SOX. The reason is, it generates only one short pulse per mains halfcycle, which is enough to break down the gas, but it isn't enough to maintain the glow discharge after the ignition, when the electrodes are still cold. The 220V is not enough to support the cold electrode glow discharge. And without this glow discharge the electrodes can not heat up, so the lamp get stuck in just the ignitor genersting tiny flashes.
You need the dedicated SOX ignitor, which works in a completely different way. It generates HF voltage, which gets superimposed onto the 60Hz (in your case) ballast OCV, so adds up to an equivalent of 400..600V OCV. And this then not only ignites the discharge in the SOX arctube, but as well delivers enough current into the large voltage drop glow discharge afterwards, so the electrodes get enough ion bombardment so they heat up and reach the thermionic emission, so allow the lamp to transition into the hot cathode arc discharge. The few pulses per mains cycle of the MH ignitor don't have enough current to provide this heating, even when they are able to reach way higher voltage. Unlike the MH, the SOX breaks down at way lower, but need significant current to be delivered from the ignitor aid.
Don't be fooled, this all takes barely a second after power on, but it is essential to actually start the lamp.

Why you have to disconnect the MH ignitor: One time the lamp will fail, some connection get loose or someone will accidentally turn it on without the lamp. In these cases the lamp wont limit the voltage anymore, so the pulses from the MH ignitor would reach the 4kV at the terminals of the SOX ignitor, And this will get killed, it is designed for tye max 900V peak voltage it normally generates, not for the 4kV.
With properly working lamp connected the voltage would be limited by the lamp, so I would expect no harm, but still the circuits of both ignitors may start to interfere with each other, affecting the ignition. So the universal safe way is to disconnect the ignitor you are not going to use.

I do not mean to use both ignitors in the circuit. I am just imagining what would happen if only the MH ignitor is used and NOT the SOX one.

The SOX will be just lightly flashing and wont start. Or it will take very long to actually start the lamp (beyond just the ignitor flashing).
And this prolonged starting attempts may actually wears the electrodes (not being 4kV ignitor, but giving just few pulses without the glow mode support is what may wear the SOX).
With some short tube (35W maybe) you may be lucky it starts within seconds so the wear wont be that extensive, but I would expect it will be very unreliable.

So, is it true that if a 35w SOX ignitor is to be used on a 35/39w magnetic MH ballast, it will run 35w and 55w SOX lamps properly?

And if a 90w SOX ignitor is to be used on a 70w magnetic MH ballast, the ballast will run the 90w SOX lamp properly?

So, is it true that if a 35w SOX ignitor is to be used on a 35/39w magnetic MH ballast, it will run 35w and 55w SOX lamps properly?

And if a 90w SOX ignitor is to be used on a 70w magnetic MH ballast, the ballast will run the 90w SOX lamp properly?

First general statement: If it is not rated officially by the maker, and it obviously is not, there is no guarantee. So there is NO GUARANTEE any of these combinations will work flawlessly.
What I'm trying to explain are the conditions required to be fulfilled to at least having the chance to work somehow, so it could be worth investing into the gear or lamp and trying it out. But always be prepafed for the situation of the thing not working.
I've never made any of these experiments and without extensive testing no one is going to guarantee anything.

For the 35/55W on a 39W MH ballast: Based on the fact 35/55W lamps are operated with series choke and that parallel SOX ignitor (that has to be rated for both 35 and 55W SOX), my guess it should start properly on the 39W MH ballast. But doublecheck the 39W MH ballast's output current: I'm rememering it as 0.5A, so 20% less than the 0.6A you wrote the 35 or 55W SOX need. So if that is the case, the SOX will start, but never reach full output.
Be sure to check the ballast output current. What the label used to show is the ballast input current, so not the parameter you need. You have to dig into the detailed datasheet or standard (either lamp or ballast), I can not confirm it myself.

For the 90W on a 70W MH: The 125V of an arc voltage seems to me quite high for just about 220V OCV the MH ballasts use to have, so there is very strong risk it wont work.
Maybe someone experienced with SOX installations, e.g. from the UK may tell, if 90W SOX were ever officially operated with just a series choke ballast (and igniter) on 230 or 240V?
Or was it only operated on an autotransformer or hybrid (a choke with a center tap to connect a capacitor towards Neutral) ballast on 240V mains?
If only autotransforme or hybrid ballasts were ever used on 240V (and not a plain series choke with ignitor), then it very likely wont work on the US 70W MH ballast with any igniter.

Many superimposed MH ignitors do in fact generate a condensed block of few pulses at each AC cycle (but only in one half wave)

Some ballast dependant ignitors (that use the ballast tap) on the other hand do only generate infrequent pulses, but they have significant energy - An ES50 for example dumps 2.2uF 220V into the ballast tap - This is quite big compared to many other ignitors

Many superimposed MH ignitors do in fact generate a condensed block of few pulses at each AC cycle (but only in one half wave)

Some ballast dependant ignitors (that use the ballast tap) on the other hand do only generate infrequent pulses, but they have significant energy - An ES50 for example dumps 2.2uF 220V into the ballast tap - This is quite big compared to many other ignitors

But it is way too few to support any glow discharge electrode warmup.
With high pressure lamps it is not needed, because these lamps start with very low pressure so way lower anode column drop than normal operation, which gives a good headroom for the cold electrode glow discharge without any extra voltage boost. Low pressure lamps are already close to operating characteristics for the plasma itself, so the extra 100V on the electrode drop has to be covered by the ballast being able to deliver significant current into such higher voltage state. The high pressure ignitors are just able to provide the initial gas ionization, but even with the more pulses (they are proportionally weaker in their energy), they are lacking the current capability the SOX requires.

Just a side note:
For my SLI/H 200W/HO lamp I use a rapid start ballast for VHO (PG) 96” tube which has a wattage of 215W. Our Swiss made ones do use a line voltage of 380V two phase. I run my 200W lamp very successfully on that ballast (with two leads off) for hours but I connect the ballst for safety measures on a variac and turn down the voltage to 360-370V as now our official line voltage is 400V and that will overload the lamp somehow.

May that work in the US as well? Many of you in the US have VHO PG 96” ballasts and some of you have the SLI 200W lamp so I wonder if there is someone who’s dare enough to try this?