Need some help with an oscillator circuit idea.

[RayRay1132]

Im working on making a homemade high speed (around 500hz) trigger tube/neon bulb oscillator and am wondering if my circuit idea would actually work. My idea is to have a capacitor charging through a resistor that reaches a certain voltage and a trigger tube fires. I was wondering how to make it oscillate? My initial thought was to run a relay coil in series with the tube so when it fires it would cause the relay contacts to short the cap starting the process all over again. Does anyone know if this will actually work in practice?

Horribly drawn schematic below lol.
Thanks in advance -Ray

 

[RayRay1132]

 

[crutschow]

Won't the trigger tube firing, lower the capacitor voltage?

 

[RayRay1132]

Won't the trigger tube firing, lower the capacitor voltage?

It would but only to a certain point (I think), I think fully discharging the capacitor is more reliable

 

[AnalogKid]

It would but only to a certain point (I think),

Correct. And that point is . . . ?

ak

 

[RayRay1132]

Correct. And that point is . . . ?

ak

I'm not sure entirely, I figure for a more reliable oscillator shorting the cap would be the best option

 

[rjenkinsgb]

A neon in series with the trigger coil, across a capacitor charged by a resistor, will inherently oscillate as the neon switches to a low resistance when it fires and discharges the cap, until the voltage is so low it extinguishes.

You may also be able to get it working using a small thyristor triggered by a diac, in place of the neon.

A relay will not work consistently at that type of speed, but a simple neon trigger will work fine.

 

[AnalogKid]

The cap does not have to be discharged all the way down to 0 V for the circuit to be reliable. As long as it discharges down to a repeatable point, the output frequency will be stable. So, what would cause the cap to stop discharging at a voltage greater than 0 V ... ?

BTW, this year is the 100th anniversary of what you are doing.

ak

 

[AnalogKid]

A neon in series with the trigger coil, across a capacitor charged by a resistor, will inherently oscillate as the neon switches to a low resistance when it fires and discharges the cap, until the voltage is so low it extinguishes.

You may also be able to get it working using a small thyristor triggered by a diac, in place of the neon.

A relay will not work consistently at that type of speed, but a simple neon trigger will work fine.

It is less complicated than that, but I was hoping he would figure it out on his own with just a little guidance.

ak

 

[RayRay1132]

It is less complicated than that, but I was hoping he would figure it out on his own with just a little guidance.

ak

I'm aware I could just make a neon oscillator without the relay but I was hoping to use a dual switch relay to switch a slightly bigger load than what the neon circuit alone could handle

 

[crutschow]

I think fully discharging the capacitor is more reliable

There is no reason to discharge the capacitor below the point where the neon bulb extinguishes.
Why do you think fully discharging the capacitor is "more reliable"?
Reliable how?

 

[danadak]

https://www.tiffe.de/roehren/neon.pdf

Might be useful.


Regards, Dana.

 

[AnalogKid]

I'm aware I could just make a neon oscillator without the relay but I was hoping to use a dual switch relay to switch a slightly bigger load than what the neon circuit alone could handle

That's a pretty important detail to leave out of the original question.

The issue is the relay coil current, because a neon bulb is not a power-handling device. With what used to be called a "plate relay", a relay with a very high resistance coil, the relay coil could be the current limiter for a standard neon bulb oscillator.

If you can't find the right coil resistance for this to work, you can add a small MOSFET to the standard oscillator circuit as a relay coil driver.

How much current do you want the relay contacts to switch? This is a major factor in determining the relay coil power.

And as above, 500 Hz is very fast for a standard relay.

ak

 

[rjenkinsgb]

I'm aware I could just make a neon oscillator without the relay but I was hoping to use a dual switch relay to switch a slightly bigger load than what the neon circuit alone could handle

If you want to switch a load, drive a transistor from the neon osc or use a transistor or IC oscillator controlling a power device. Mechanical relays the operate at accurately at high speeds are very rare and expensive!

An old Carpenter relay may work consistently up to possibly about 100Hz with a bit of luck, tuning and appropriate drive circuits... They were the "go to" relay for passing serial data - about 60 - 70 years ago.

With electronics and optocoupler alternatives, they are long obsolete.

https://flic.kr/p/8JtRnr

 

[Nigel Goodwin]

If you want to switch a load, drive a transistor from the neon osc or use a transistor or IC oscillator controlling a power device. Mechanical relays the operate at accurately at high speeds are very rare and expensive!

An old Carpenter relay may work consistently up to possibly about 100Hz with a bit of luck, tuning and appropriate drive circuits... They were the "go to" relay for passing serial data - about 60 - 70 years ago.

With electronics and optocoupler alternatives, they are long obsolete.

https://flic.kr/p/8JtRnr

As his entire premise is wrong to start with, does it really matter? - and if you want to use a relay (for some bizarre reason) why use a neon as well?.

 

[RayRay1132]

As his entire premise is wrong to start with, does it really matter? - and if you want to use a relay (for some bizarre reason) why use a neon as well?.

How is my entire premise wrong exactly? I have a bunch of old parts and I like to build stuff the old fashioned way even if it isn't the most efficient way of doing things. I also wanted to use a neon bulb because I have a bunch of them and I think it kinda looks cool.

 

[RayRay1132]

If you want to switch a load, drive a transistor from the neon osc or use a transistor or IC oscillator controlling a power device. Mechanical relays the operate at accurately at high speeds are very rare and expensive!

An old Carpenter relay may work consistently up to possibly about 100Hz with a bit of luck, tuning and appropriate drive circuits... They were the "go to" relay for passing serial data - about 60 - 70 years ago.

With electronics and optocoupler alternatives, they are long obsolete.

https://flic.kr/p/8JtRnr

I didn't even think of driving the transistor off of the neon bulb. I guess that will work and be easier than messing around with relays.

 

[Nigel Goodwin]

How is my entire premise wrong exactly?

The idea of adding a relay - completely pointless - neon oscillators are extremely old (and crude) circuits, no on has added a relay during the last 100+ years.

 

[danadak]

If you look at pages 63 - 65 there are relay circuits, but I think Neon bulbs
used were capable of more current. And use of the "Sigma Sensitive" relays
of yore used in various circuits, like RC controlled airplanes. These relays
achieved control thru use of many turns windings. Or use the circuit using
a transistor to boost current.

You can occasionally find the relays on eBay but for some hefty prices.
The bulbs called out.....lost to time.....?

https://www.tiffe.de/roehren/neon.pdf

Note you could sub a OB2 or OA2 regulator tube for the Neon as that is capable of
a lot more current, still fairly available. Or the RCA 991 bulb.

0A2, Tube 0A2; Röhre 0A2 ID4071, Voltage Regulator, single | Radiomuseum.org

Tube 0A2 or Röhre 0A2 ID4071, Voltage Regulator, single, Miniatur-7-Pin-Base B7G, USA 1940 and Power-supply shown. Radio tubes are valves.

www.radiomuseum.org

http://www.r-type.org/pdfs/0a2.pdf

http://www.r-type.org/pdfs/991.pdf

Regards, Dana.

 

[Nigel Goodwin]

We used to play with neon oscillators at work sometimes, simply because we'd got plenty of TV's (so no problems with an HV supply), and we used to have neons in stock Resistor, capacitor, neon - nice little flashing light!.

For those perhaps too young to remember?, for a period of time TV's used touch buttons to change channels (remote control was rare), and these commonly used neon bulbs both to display which touch button was selected, but also to actually latch the button.

But neons have never been terribly reliable devices, so we used to keep considerable numbers in stock for replacements.