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Also note that on lower resistance settings on multimeters, typically the higher the voltage on the leads. Use the 100-ohm setting for diodes if the meter does not have a diode checker setting.

This oscillator needs to run from a DC supply at a set voltage, but will run from 5V up to 15V DC no problem, and won't require much power, probably 250mA at the most steady-state. The rail power can be "whatever" it needs, and the high voltage will simply "ride" on top of it.

Good luck. These things are tough without a few other tools to support you, like a multimeter with a diode tester, or even better, a cheap oscilloscope.

Thanks for the info!

Just now as I was testing the transistor with the handcar on the tracks, I touched a 14 volt light bulb's leads to the transistor leads and I accidentally / temporarily shorted posts 1 & 2 (or 2 & 3), and then I smelled burning as the handcar took off at what would appear to be an extra 4-5 volts on the rails. I quickly shut it all down in a split-second. The transistor got very hot very quickly. So it is fried! So now awaiting the other transistors on order to possibly repair what I did wrong. Hope that is all I ruined, the transistor. Good thing I ordered 4 more! Supposed to arrive tomorrow, but won't be able to work more on it until Thursday.

Thanks, again, everyone!

Well, live and learn! Fun and frustration, at the same time!

Take care, Joe.

Now the 3rd transistor is soldered in place -- no more "testing" to cause a short.

Would the wattage rating of the resistors make a difference? One is about 3 watts and the other is 10 watts. Should they be balanced?

Also, when I hooked up the transistor the wrong way with the 1st and 3rd pins reversed, is it possible the circuit still worked? Seemed I got a slight shock from the rails with the pins reversed. Can't feel any shock or tingling now.

I do notice a slightly increased spark when I lightly touch one wheel to the rail, other than that it is hard to know it is working. The sintered metal wheels tend to spark a little under normal circumstances DC or AC. I can feel the slight heating of the transistor at times. Years ago when I built a HF AC lighting circuit, you could get some interference on a radio when you held the antenna it over the circuit.

Aside for the price of the bell transformer, the circuit is very inexpensive. Perhaps I could see a bigger difference with HO gauge equipment.

Thanks, Take care, Joe.

O.k. Folks,

Here are the missing pieces: I was connecting the cap that protects the throttle incorrectly and I also didn't have a little 0.1 mfd cap across the motor's leads. Now, great sparks! And a little tingle on the fingers, too!

Thanks everyone!

Take care, Joe.

Glad to hear you got it working!

Regarding your questions from before...

The wattage of the individual resistors is largely irrelevant in this case; the resistance is what matters. As long as they're able to dissipate enough power without burning up you're good, and based on the schematic I'd say the wattage rating of both of those resistors is overkill.

Bipolar transistors will still function (sort of) when connected "backwards", i.e. emitter and collector reversed; but the gain will be much lower (which may or may not prevent the circuit from functioning), and depending on the voltages involved they may suffer damage over time. In any case, based on the pinout it looks like you originally reversed the emitter and the base, in which case I would not have expected the circuit to work at all.

Thanks for the information!

I don't know how I ordered the one resistor at 10 watts, but after seeing that tiny transistor, I realized that I they both seemed so heavy-duty by comparison. I will build another one with different resistors and a smaller rectifier, just to keep the circuit more compact. I also bought a heat sink that is way too big. I will try to pop open an old wall-wart to see if I can get a smaller center tapped transformer so everything can fit neatly in a small project box. But like they say -- "If it ain't broke, don't fix it!"

Take care, Joe.

Hi Folks,

Still playing with the circuit!

Because I don't have a way to test the output, I was wondering if a neon bulb, similar to those in the typical outlet tester, and perhaps like the one that was used in the Relco, could detect the HF AC. Using a regular outlet tester, I can only read a "spike" through the coil the DC goes through (was the primary of the bell transformer) as the field is breaking down when rail contact is lost (I guess?), but this happens even when the other side of the transformer (was the secondary) is disconnected from the circuit with the transistor. Another issue, in 3 rail track, the ties are metal with a tiny piece of electrical "fish" paper insulating the center rail (outside rails tied together both physically and electrically by the metal ties. I was wondering if the fish paper, if slightly damp and perhaps not the greatest quality, could negate the HF AC. It might be slightly conductive to the HF AC?

So, in other words, would those little neon bulbs (with the right resistor) be able to detect the 350 volts but at such a small amperage?

Any thoughts greatly appreciated!
As always, thanks!!!!!!!!!

Take care, Joe.

Yup, a neon bulb (NE-2 type) should work as an indicator. I would use a series resistor of approximately 350K ohms to prevent damage to the bulb.

A Neon bulb begins to ionize at around 90V, and then the impedance goes rather low as the gas is ionized. So you go from several Gigaohms down to a few hundred ohms. You will need a series 47K ohms or higher resistor mostly to prevent the oscillator from stopping once the bulb lights briefly.

If enough voltage is formed, you can simply hold the neon bulb up near the transformer, and it will light if you are holding the leads. The picture you showed indicated that is how they are detecting the presence of the high-voltage field.

Yup, neon bulbs require very little current. I recall discovering (many years ago, I think I was still a teenager) that you could get them to flash with just static electricity.

just brew it! wrote:

Yup, neon bulbs require very little current. I recall discovering (many years ago, I think I was still a teenager) that you could get them to flash with just static electricity.

That also works on full-size fluorescent light tubes

ludi wrote:

That also works on full-size fluorescent light tubes

Paging Tesla to the lab, STAT!!

Hi Folks,

Thanks for the help and bulb number. Looking forward to trying it!

I have a Christmas tree light bulb tester that beeps when placed over a wire with AC running throught it, and at times I get the beeping indicating AC at a higher voltage. The device doesn't detect low voltages but does beep over the core of the bell transformer when the HF AC should be flowing. The device is called the "Light-keeper Pro." I have gotten the beeping, at times, when held against the wire to the track, but it seems to be sporadic.

Will keep you all posted on my efforts.

Take care, Joe.

The bulb tester is looking for 60Hz, not the 20,000Hz or so the circuit is running at. So it is not likely to be a reliable indicator. The neon bulb? Perfect... Even a small compact fluorescent bulb from a dead display backlight may work, depending on the condition of the bulb.

Another fun project with neon bulbs is to make a high-voltage energy harvester to collect atmospheric ions, and use the bulb as an indicator.

I took a long wire and zig-zagged it between two poles for my mom's laundry lines when I was a kid, using nylon string as an insulator to suspend the wire, and ran one end of the wire down to a neon bulb with a 100pF 250V capacitor across it. The other lead of the bulb went into the dirt. The bulb would flash every couple of seconds on a clear day with the wire only 6' off the ground. Draping strips of paper towel over the wire and setting it on fire would increase the flash rate as the plasma of the fire is an excellent conduit of atmospheric electricity.

The cool observation of this is only one lead inside of the neon bulb lights with the DC current flowing into it. Clear days it would always be the lead of the antenna. But when storms were in the area, the direction would switch. Oh, and when a good storm was in the area, the bulb would be extremely bright and constant at times until the insulating string got wet. I never got to test it in a winter storm, but I hear the atmospheric electricity in those can be very high even though there is no lightning.

It is impressive to see what is going on in the atmosphere that we are not aware of, if you have some idle time (yeah, right) it is an easy and fun experiment.

liquidsquid wrote:

Another fun project with neon bulbs is to make a high-voltage energy harvester to collect atmospheric ions, and use the bulb as an indicator.

I took a long wire and zig-zagged it between two poles for my mom's laundry lines when I was a kid, using nylon string as an insulator to suspend the wire, and ran one end of the wire down to a neon bulb with a 100pF 250V capacitor across it. The other lead of the bulb went into the dirt. The bulb would flash every couple of seconds on a clear day with the wire only 6' off the ground.

Hail, fellow uber-geek! I think that makes you one out of less than half a dozen other people I've encountered who did wacky stuff like this when they were a kid...

Got a crystal radio kit and a Radio Shack 65-in-one electronic projects kit when I was like 10 years old, and it was all uphill (downhill?) from there. Scavenging parts from dead TVs and other electronics (it's a wonder I didn't give myself lead poisoning from all the solder fumes), wiring up home-brewed bench supplies (also somehow managed to avoid electrocuting myself), etc... I also remember taking money I'd saved up (I must've been like 12 years old at the time) to the currency exchange to buy money orders, so I could mail in hand-written parts orders (no Internet back then!) to Jameco and Digi-Key. My dad even got me an oscilloscope for my 8th grade graduation. Best. Present. Ever!

just brew it! wrote:

liquidsquid wrote:

Another fun project with neon bulbs is to make a high-voltage energy harvester to collect atmospheric ions, and use the bulb as an indicator.

I took a long wire and zig-zagged it between two poles for my mom's laundry lines when I was a kid, using nylon string as an insulator to suspend the wire, and ran one end of the wire down to a neon bulb with a 100pF 250V capacitor across it. The other lead of the bulb went into the dirt. The bulb would flash every couple of seconds on a clear day with the wire only 6' off the ground.

Hail, fellow uber-geek! I think that makes you one out of less than half a dozen other people I've encountered who did wacky stuff like this when they were a kid...

Got a crystal radio kit and a Radio Shack 65-in-one electronic projects kit when I was like 10 years old, and it was all uphill (downhill?) from there. Scavenging parts from dead TVs and other electronics (it's a wonder I didn't give myself lead poisoning from all the solder fumes), wiring up home-brewed bench supplies (also somehow managed to avoid electrocuting myself), etc... I also remember taking money I'd saved up (I must've been like 12 years old at the time) to the currency exchange to buy money orders, so I could mail in hand-written parts orders (no Internet back then!) to Jameco and Digi-Key. My dad even got me an oscilloscope for my 8th grade graduation. Best. Present. Ever!

I think my most off the wall was tapping into the spark plug wire on our lawn mover and running the line into my room for an HV source. I could gen about 3/4" of an inch spark before the engine would die. And now, back to your regularly scheduled thread....

--SS

Yeah, I was so "geeky" that I sat in the basement and made rail guns and 1.5MV voltage multipliers rather than sit in a basement with my friends playing D&D and other long, boring strategy board games. Yeah, I can relate very well to Big Bang Theory.

As I kid I would ride my bike from my parent's house into the City of Rochester to Goldcrest Electronics, a pretty good haul, just to save some money rather than go to Radio Shack and get ripped off on resistors and the like. Built some pretty cool stuff for my age that my friends just didn't "get". My parents were very supportive, but I think they chose to ignore how dangerous some of it was.

It led to a pretty fun job at Ramsey Electronics for a dozen years, and I got to re-use some of that knowledge in making some cool hobby kits. Crystal radios for one... many of the kits still on that site were created by me (at least not the imports) 8 or more years ago.

Pay was crap though.

serkan90 wrote:

I looked at the datasheet and I think it is not a good replacement for the BD137 because of its typical frequency which is around 190MHZ and it will create a problem by providing the maximum gain to 190 MHz signal only. So I think you should look for a transistor with large operating frequency range as it is very difficult to obtain a signal of particular frequency.

That's not how typical transistors work. Operating frequency specs are meant to be interpreted as an upper limit.

Yup, the replacement has been working for the past 3 years.