Do you think that two different LED's will work in the very same way?
Do you think that two different core's will operate in the same way.
What about different transistor's?
What about different numbers of turns for each coil,or the wire size used?.

How you can say that the two different circuit's will/should operate very close to the same is beyond me.
Like i said MH,you really are not well versed in JT circuit's.
The fact that you do not know why the transistor stays on longer,and the frequency lower's when the base resistance is decreased,truly shows you have so much left to learn.

Facts are facts MH,and your fairy tails have been proven to be just that--fairy tails.

The fact that you do not know why the transistor stays on longer,and the frequency lower's when the base resistance is decreased,truly shows you have so much left to learn.

Brad:

Presumably two different LEDs won't make much of a difference.
Assuming the cores are about the same size and both are high-permeability, not much difference.
Ditto for the transistors.

The number of turns for each coil will indeed make a difference.

There is no reason for your Joule Thief to run so fast and I think something is amiss.  You clearly have a serious design problem because you have the Joule Thief death spike.

Please go ahead and explain why it is happening.

MileHigh

Tinman,

Moving the scope ground to the transistor base is not a very good way measure base current.  Any time the base voltage is less than the Vbe turn on voltage or is reverse biased, the base appears mostly capacitive (combined with a small amount of leakage current).  Moving the scope ground lead to the base changes the capacitance at the base.

A better way would have been to keep all scope grounds on the battery minus and use both scope channels and probes to measure both ends of the 10R base resistor.  With both scope channel vertical gains set identically (ca 20mv/div) invert one channel and then add them together (or use a math function to subtract one channel from the other).  This allows you to make a differential measurement across the 10R with minimal capacitive loading (particularly if you use 10X probes).

Also, you only have two channels so you should be taking advantage of the external trigger input.  It has limited "viewing" function, but if used smartly, it can be used to keep a marker on the screen at all times that indicates a particular time point in the waveform being observed.

That said, I do not believe the base current flowing thru L2 is acting in the manner you surmise.  In fact, I would think that current flowing thru the base (and L2) would generate a flux in opposition to that generated by current flowing thru L1.

You should consider measuring the Vce and Ic at the two base current extremes you are using.  You may find that Vce or Ic varies with Ib.  To do so, instead of making videos, consider creating six scope captures.

I would add a 1R resistor between the transistor collector and the L1/LED junction and connect the scope grounds to the emitter/battery junction.  I would then choose two base resistances to measure operation with such as 1K and 500R.  I would connect a third probe to the external trigger input and connect that probe to the L1/LED junction and trigger on the rising edge (which is the straightest edge in your waveform).

The first capture would be with the CH1 probe at the pot/10R junction in the base leg, and the CH2 probe at the collector of the transistor with the pot set to 1K (or using a fixed 1K).  The next capture would be identical, but with the pot set to 500R.  These two captures would let you see any change in Vce as the base current is changed between the two base currents.

The next capture would be with the CH1 probe moved to the L2/LED junction (i.e., the other end of the collector's 1R).  Using 1K as a base resistance, set both scope channels so that there is a good signal, and then invert and add (or subtract using math) to measure the differential voltage across the 1R, which is the collector current Ic.  The next capture would repeat this test using the 500R base resistance.

At this point you would have the collector to emitter voltage (Vce) and the collector current (Ic) when using the two base currents with 1K and 500R base resistors. 

We already know the base current is increased when the base resistor is changed from 1K to 500R, but it would be useful for further analysis of turn on, etc, to measure the base current under the same two operating conditions.

As was done to measure the collector current, make a capture using both probes to measure the difference voltage across the 10R resistor at the base using first the the 1K base resistance and then repeat this test making a second similar capture using the 500R base resistance.

You would now have a set of six scope captures.  Because the external trigger input was used, they are fairly closely time aligned.  The first pair of captures gives you Vce data, the second pair gives you Ic data, and the third pair gives you Ib data. Each pair provides data when the base resistance is set to 1K and 500R.

You might consider doing all these tests using your bench supply set to a known voltage as the battery voltage may change over the time period needed to make these six captures.

Although its just a joule thief, making these captures would be good measurement/scopology practice..

Just my 2 cents...
PW

There is no death spike-you need to understand the circuit, and why there is a spike across L2 when the transistor becomes open. It all has to do with the number of turns on each coil-the more turns, the higher that L2 spike will be-there is nothing out of the ordinary with that spike.

Your pitch about currents through L1 and L2 adding up to put more magnetic energy into the core is dead wrong.  See my earlier posting.

It's pretty obvious this time that reducing the base resistance barely increases the intensity of the LED and it can only be picked up by the light meter.  Changing the base resistance makes no change in the LED intensity for the naked eye.

For the 10-ohm CVR setup, you are looking at a massive anomaly where the L1 coil is discharging straight into the L2 coil via the 1k resistor and sucking some life out of your Joule Thief and you are not saying anything about it.

For the 10-ohm CVR setup, you can see that lowering the base resistance gives you more current through the base-emitter diode of the transistor.  The assumption is that this is excessive current that is doing nothing for you except wasting energy, just like I have said several times.

I don't believe that putting a current limit on your bench power supply will emulate a nearly discharged battery's output impedance.  I would think that you should measure the actual output impedance of a nearly discharged battery of a given size and chemistry type, and then simply put the appropriate resistor in series with your bench power supply.

So, the variable base resistor is not doing much good at all for you in this clip, and then there is the discovery of the massive anomaly in your clip.  I have a few more minutes to watch to see if you have anything to say about it.

Lol
!!!!huge!!!! spike you say lol
Did you look at the VPD setting on CH2 MH ?-and how narrow the time period is for the !!!huge!!! spike lol.
lets not talk about junction capacitance--we all know you hate that subject,and that it may provide some proof of the miller capacitance effect being the cause of the cool joule being able to operate without any inductive coupling between L1 and L2.
It's all coming back now to bite you on the ass--and you are the one showing your own errors lol.

I love it when a plan come together

Brad