Hendershot Replications

[NOMDI]

What transformers are you using? Make sure they are identical, I've got 2 transformers from the same maker but they are not identical

I guess it could be possible to modify the windings number to get perfect matching, if needed. I'm not sure that at Hendershot time, transformers matching was as good as now...

[mlurye]

I bought a pair on ebay. No name, just "PRODUCTS UNLIMITED ,USA" .
120V to 24 V, 24 VAC markings.

I measured : 0.389 H and 0.020 H for the first one,

0.411 H and 0.021 H for the second one...

I don't know if these values are close enough for the Hendershot device. Maybe I should make a resonance test...

You are off, same as mine I bought 2 more from the same maker, so hopefully 2 of 4 will match.

[NOMDI]

What transformers are you using? Make sure they are identical, I've got 2 transformers from the same maker but they are not identical

I bought a pair on ebay. No name, just "PRODUCTS UNLIMITED ,USA" .
120V to 24 V, 24 VAC markings.

I measured : 0.389 H and 0.020 H for the first one,

0.411 H and 0.021 H for the second one...

I don't know if these values are close enough for the Hendershot device. Maybe I should make a resonance test...

[NOMDI]

@mlurye

I forgot to tell you that this result has been achieved with a horseshoe magnet placed over the coils which, i noticed, helps to decrease the voltage running threshold...

[mlurye]

What transformers are you using? Make sure they are identical, I've got 2 transformers from the same maker but they are not identical

[NOMDI]

NOMDI did you build your coils or just collecting parts for now?

I'm building my coils but they are not ready, not yet... I also collect the other parts for the device. Unfortunately I don't have a lot of time to build faster...

I've made an experiment with a buzzer (the model used by morper44) : by bending the electrodes and the clapper holder, It works with a very low voltage 0f 0.2V DC. Don't start by itself but need a very small impulsion with finger... then runs with a very very small, mosquito-like, sound. I'm surprised it can run with a so low voltage...

[mlurye]

NOMDI did you build your coils or just collecting parts for now?

[NOMDI]

morpher Good point. That's how I was adjusting my caps, but I was compressing it all around not in one spot.

@mlurye
Hi, i've just ordered microwave capacitors for tests...Thanks for the idea

@all
Don't you think that instead of clamping the handmade capacitors it could be better to add a 500 pF variable air capacitor in parallel, like vintage big and ceramic capacitors used in radio ? Just to avoid unwanted variations and to get a precision adjustment ?

[mlurye]

I believe that is simply the hand-made capacitors with an ability
to compress the cylinder using a c-clamp.
You can see in another photo, the one with the bulb lit,
him adjusting the c-clamp.

This amounts of a variable capacitor in the nano-farad range.

morpher Good point. That's how I was adjusting my caps, but I was compressing it all around not in one spot.

[morpher44]

caps with c-clamps

In this book on page 28 Hendershot in Schematic Drawing mentioning "Resonance Tuner", I wonder what it is and how does it work? (Also you can see this tuner on a picture above)

I believe that is simply the hand-made capacitors with an ability
to compress the cylinder using a c-clamp.
You can see in another photo, the one with the bulb lit,
him adjusting the c-clamp.

This amounts of a variable capacitor in the nano-farad range.

[mlurye]

From the Archives of Lester J Hendershot by Mark Hendershot In this book on page 28 Hendershot in Schematic Drawing mentioning "Resonance Tuner", I wonder what it is and how does it work? (Also you can see this tuner on a picture above)

[morpher44]

capacitor change

I noticed interesting thing about hand made caps.
I was measuring capacitance of both caps with different frequencies.
With 100Hz and 120Hz it mesures ~7.8nF.
With 1kHz ~5.9nF. (Both caps showing same result)

@mlurye
Interesting. What do you think is going on?
I would guess that perhaps at higher frequencies, the plates
push apart more ... creating a larger gap between plates ..
resulting in smaller capacitance.
The ionic pressure may fill it up sort of like a balloon filled
with gas, moving the plates away from each other.

[mlurye]

I noticed interesting thing about hand made caps.
I was measuring capacitance of both caps with different frequencies.
With 100Hz and 120Hz it mesures ~7.8nF.
With 1kHz ~5.9nF. (Both caps showing same result)

[mlurye]

Very nice coils, congratulations !

Do you have any link of the paper in oil caps you used ?

NOMDI you can use any MW cap.

[NOMDI]

Here is my setup. I don't have buzzer yet. And my transformers are not good

Very nice coils, congratulations !

Do you have any link of the paper in oil caps you used ?