Stevens ST-75 Tester first time user questions

[Buccaneer]

Just tried out a Steven’s ST-75 tester for the first time
this morning, on components from a 1956 Evinrude Lightwin.
Old coils with a few hairline cracks, and old condensers.
Both coils tested tested okay under load on the amperage
test, in spec, and produced a nice spark.
Both tested okay on primary and secondary resistance.
I then used the "probe" on one coil, while running the amperage
check, to check for any external leakage / arcing.
The probe did produce some tiny arcs around the clip
that holds the coil onto the laminate.

Q. – Could this be a normal occurrence from the
magnetic field induced while testing, or is there
indeed some leakage?

When I tested the condensers, neither passed the
"leakage" test. I then tried two NOS Presolite
Wico condensers, and they both failed the
leakage test.
I then tried a Digi-Key .20 UF capacitor, and
it passed with flying colors.

Q. Before I start throwing away all my old condensers,
I thought I’d ask "How critical is this test?"
Some seemed to fail the test worse then others.
Unfortunately, I have no new OMC condensers
on hand to test and compare.
Thoughts?

Q. How does one test a Zephyr type coil, that being
a coil with two secondaries?

Thanks!

Prepare to be boarded!

[Tom]

When under test by the Stevens unit, the spark Is not generated under compression. So there is less load on the coil than when trying to run a motor. If there is leakage with you test it, it will be worse under load. The coil may work in the motor, but not dependably.

If the condenser tests bad, it’s probably bad. I’ve tested new ones that failed, and when I tried them in a motor, they did not perform well.

The Zephyr coil has only one secondary winding, but instead of grounding one end to the same ground as the primary, both ends of the secondary come out of the coil for high tension wires to attach. I don’t have a Stevens 75, but I do have one of the older Stevens units. The wire that usually goes to the mag plate (ground) just goes to one of the high tension terminals. The one that normally goes to the spark plug wire just goes to the other one.

Tom

[joesnuffy]

I have a Stevens ST-75 tester and love it. Its an awesome tool. Wish I had one when I was a lad.

It is very accurate at testing condensers and their values etc. I did notice when testing the used stand up condensers on West Bends/Scott Atwaters that the brass condensers for the most part tested O.K. the steel stand up condenser don’t Just curious if anyone has experienced that?

Most used condensers I test don’t pass leakage test I think its because their paper construction inside not like the Orange Drop Panasonic Film condensers/capacitor inside.

Generally new OMC condensers do pass the test.

The digikey Orange Drop Film condensers/capacitor pass the leakage test faster than any condenser I have ever tested they immediately fall into range when tested for leakage they don’t take a second or 2 like OMC paper ones that pass. I believe omc makes their condensers from paper not film. Panasonic orange drop ones are made from with film which is more reliable. I put a couple of orange drop condensers in a 40hp 1956 Scott I am working on and it idles awesome and very steady no flucuations.

Leads me to believe the Orange Drop Capacitors would be way better at keeping points from burning. Just my humble opinion and their relatively cheap. Some folks here that use them could say how they do in comparison with point burning.

Great video on capacitors/condensers.

https://www.youtube.com/watch?v=2bBifpRa890

When testing coils not all are equal. I have noticed some take more power to produce spark. Once you have tested several you will know if your having to give one more power than normal to get the spark. I guess that is kinda a learning curve with using that piece of equipment each one will vary a bit. I would try and replicate the spark leakage jumping from a new coil around the laminate clip I bet that is a weak coil your testing.

Hope that helps,

Joe

[Buccaneer]

Tom, thanks for the explanation on the Zephyr coils. I don’t have
one loose to play with, but that day will come!
Joe, thanks for your observations on testing the different types
of condensers. Will be interesting to see if others have
similar experiences.
Had to fast forward some of the 1965 film footage……
you didn’t warn me there were "Test" in it, lol.
The next video that popped up was better at
explaining "how" a capacitor holds a charge.

https://www.youtube.com/watch?v=PAPGTuvHSRo

Thanks!

Prepare to be boarded!

[billw]

I also agree the Stevens tester works great. I have seen those small arcs you’re talking about. I can’t explain them but have run coils that have them in that location and they have been fine. Maybe some kind of secondary induction but it’s way above my pay grade. The leakage probe, when it finds a leak, will draw a arc that is quite pronounced, between an eighth and three eights of an inch.

The condenser leakage test is awesome. It really separates the men condensers from the boy condensers, if you will. On the Mercs, you will find almost every single original Phelon condenser will test bad. New ones will test good. And even though a lot of old Phelon condensers will allow enough spark to run, you will easily notice the difference between a new one and an old one, when doing an open gap spark test. When the Stevens says they are bad, they ARE bad.

Long live American manufacturing!

[Buccaneer]

Bill, regarding the little arcs I experienced while probing the coils….
I had the same thoughts that it was some kind of "induction" current,
and it’s also way above my pay grade 😮
I just ordered ten more Digi-Key P12106-ND .2 UF caps last night.
I keep saving a lot of the old condensers I remove……. "Just
in case I might need them some day"….. guess I should
just throw them out, lol.
Thanks.

Prepare to be boarded!

[jerry-ahrens]

I think Bill is right on the coil test. I’ve also noticed this using my Stevens. If you have a leak while using the probe test,
it will throw a pretty good spark. And the cracks will be very noticeable on the coil. As far as the capacitor leakage test, if they fail this, they are shot. I too, have tested quite a few Wico screw top condensers that fail on the Stevens. I’ve also had a lot of used OMC condensers that appear to be ”weak” on the leakage test. Better to replace them. When you test a new one compared to the old used one, you will see the difference.

[chris-p]

For the OMC condensors, the red paper top ones seem to fail more than the newer black rubber topped ones.

[dave-bernard]

use your old condensers to mount you new caps. just gut the condensers and install the new caps. I drill a small hole in the bottom and solder the wire from the cap for the ground. it mounts easier and looks like original.

[Buccaneer]

Thanks again for your thoughts.
Dave, I have gutted Wico "screw top" condensers
and mounted caps beside them, using the old
condenser just to have a connection point,
and that worked great. I have not tried to
mount a Digi-Key cap in an OMC condenser,
as I didn’t think they were big enough around….
will have to check again.

Regarding the Stevens ST-75, there’s a knob that
says "Reverse Polarity". I didn’t see it mentioned
in the manual. Can that knob be used to switch
polarity, so you don’t have to switch wires
on an amperage test, to see which polarity
has better, or correct hookup, and hence best spark?

My "Battery / ON / AC" power switch seems
a little off. Not sure if the knob moved on the
shaft or something moved internally. Will be
easy enough to check the knob set screw.
I don’t have a battery, or desire, to try one,
but does the knob only actually have one
"ON" position, whether hooked to AC or Battery?
The switch works and powers up the unit okay,
but right now, to get the thing to power up
on AC, the knob is over on the "battery" side.
Thanks!

Prepare to be boarded!

[Author]

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