Transformer neon tester question

[Randall]

When I am testing a Hammond 125DSE OT with this neon tester: https://music-electronics-forum.com/...tential-bad-pt, I only get a lamp flash when connected to the primary side. No flashes on any pair of secondary windings. Transformer is on the bench and unconnected. I am using a 9 v supply.

Why?

[Helmholtz]

Did you try your neon tester with a known good OT for comparison?

It is essential to use a fresh battery because the low impedance secondaries draw a lot of current.
Flash brightness depends on the short-circuit current the battery can deliver.
Typically a larger 6V battery works better than a 9V battery, because it can deliver much more current.

Secondaries always give a weaker flash than primaries, because their inductance is much lower.

[Randall]

The OT is fresh out of the box, so I would assume it is good. I was using a used 9v battery, so maybe that is it.

[g1]

Also may depend on value of resistor in use?

[Enzo]

The OT is fresh out of the box, so I would assume it is good

I think the suggestion to test the procedure on a known good transformer is to verify that your test setup is working as expected. If you test a known transformer and it tests out the same as your new one, then you know it is your test that is confusing, not an indication of transformer trouble.

[GainFreak]

I only get a lamp flash when connected to the primary side No flashes on any pair of secondary windings.

This tester relies on the OT primary inductance to work properly. If the OT is OK inductance must be much higher than the secondaries' inductance which is insignificant (low number of turns).
When the neon flashes it means high inductance - the OT is good. If it doesn't that means no or low primary inductance which usually means bad OT.

[Helmholtz]

A 1.5V LR14 cell works fine on secondaries.

Agree that a strong flash at the primary typically means no shorted turns.

[tdlunsfo]

I have had issues getting a flash on certain PT/OT circuits. Seems the heater windings are always hit or miss as well as OT secondaries.

[SoulFetish]

Assuming that the 9V battery is fresh. I always find the lowest impedance winding to use and consistently get the results I'm looking for. I built mine into a permanent enclosure using a momentary switch like.. kind of like a Morse code.

Here is a short clip of me testing an Edcor transformer with the voltage connected across the secondary and neon across the primary.

[Helmholtz]

There are 2 different ways to use a neon tester.

The first one uses the voltage step-up ratio between a low voltage/impedance winding and a high voltage/impedance winding.
In this case the battery is connected to a low voltage/impedance winding and the neon is connected to a high voltage/impedance winding.
The neon will flash when the switch is closed and the stepped-up battery voltage at the other winding exceeds the ignition voltage of the neon.
This method requires little battery current but a transformer step-up ratio of 10 or higher.

The other method connects the battery and the neon to the same winding.
The neon will flash with a good transformer when the switch is opened (current is interrupted).
The principle here is self-induction which causes a high flyback voltage when the current is interrupted.
With a low inductance winding, a considerable battery current may be required, but it typically suffices to test the high voltage/impedance winding.

I think the second method is more universal and selective.