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Before putting everything on a PCB, I realized there's something else I can do in my circuit. Right now, I'm using a diode bridge to rectify AC to DC. But I have a bunch of 12X4 full wave rectifiers that I can use instead.

I found this schematic on the internet:


However, my transformer has only two output pins. This is how I believe I should connect it:

The heaters of the two triodes are connected in series, and the heaters of the rectifier are connected in parallel. Pin 6 of the 12X4 I'm not connecting anywhere, and I'm using the same ground for AC and DC. But I believe that his is doing the same as a half wave rectifier tube. Do I have this right or am I wrong?

Thanks for your inputs!

 

You have a half-wave rectifier circuit with no smoothing capacitor.
Your LEDs and triodes will be seeing 50Hz pulses.

You would be better off to use a full-wave semiconductor bridge rectifier. Don't skip the smoothing capacitor.

 

You have a half-wave rectifier circuit with no smoothing capacitor.
Your LEDs and triodes will be seeing 50Hz pulses.

You would be better off to use a full-wave semiconductor bridge rectifier. Don't skip the smoothing capacitor.

Right now, I'm using a full-wave semiconductor bridge rectifier. I was using a 2200uF/50V smoothing capacitor, but it made my circuit go bogus (ie. one of the two LEDs would stay on twice as long as the other). Without the smoothing capacitor, the circuit works fine (ie. both LEDs stay on as long as the other).

As for the 12X4 running as a half-wave rectifier, that's what I thought. But I don't know how to connect it as a full-wave rectifier. The datasheet says it's a full-wave rectifier.
12x4

 

As for the 12X4 running as a half-wave rectifier, that's what I thought. But I don't know how to connect it as a full-wave rectifier. The datasheet says it's a full-wave rectifier.

It makes a full wave rectifier with a centre tapped transformer. You will lose more supply voltage using the 12X4 than with a semiconductor bridge.

 

It makes a full wave rectifier with a centre tapped transformer. You will lose more supply voltage using the 12X4 than with a semiconductor bridge.

Alright. Thanks. I'll try to find a cheap center tapped transformer, otherwise I'll stick to the bridge. I'm not doing this to build the ultimate high-end, perfect cost-efficiency vacuum tube oscillator. I'm doing this to have fun and learn (and to use the dozens of tubes that I have). It's alright if I lose some supply voltage. Thanks for your help.

 

If you are doing this to learn then use the semiconductor bridge rectifier and install the smoothing capacitor. Fix the underlying problem.

 

Hi, all.

Before soldering everything, I wanted to try the same circuit, but using lamp bulbs instead of LEDs. I have some E-14 tubular lamps that look pretty good next to the tubes. They're 220V 15W bulbs. They won't turn completely on, the filaments glow slightly, as seen in the picture, but that looks actually better imo.



Anyway, if I replace the LEDs+Resistors with the bulbs, they won't do anything. I imagine there's not enough current. How can I modify the circuit to get the lamps to work? Thanks!

 

Give me a few days and I can set up a test bench with tubes in order to replicate your circuit.

 

Thanks, MrChips!

 

Hi, all.

Before soldering everything, I wanted to try the same circuit, but using lamp bulbs instead of LEDs. I have some E-14 tubular lamps that look pretty good next to the tubes. They're 220V 15W bulbs. They won't turn completely on, the filaments glow slightly, as seen in the picture, but that looks actually better imo.

View attachment 240923

Anyway, if I replace the LEDs+Resistors with the bulbs, they won't do anything. I imagine there's not enough current. How can I modify the circuit to get the lamps to work? Thanks!

View attachment 240924

The lamp filaments have a much lower resistance when they are not up to full temperature so you are overloading the anodes of the tubes. Lower wattage lamps (sewing machine or night light bulbs?) with series resistors might work.

 

The lamp filaments have a much lower resistance when they are not up to full temperature so you are overloading the anodes of the tubes. Lower wattage lamps (sewing machine or night light bulbs?) with series resistors might work.

Is it just an issue of resistance? Would a series resistor with these 15W lamp work?

 

Is it just an issue of resistance? Would a series resistor with these 15W lamp work?

Then the multivibrator will work but the lamps will get such a low voltage and current that they will not produce any light.

 

I tested a similar circuit with whatever components I had on hand.
The tube I used is a twin triode, 6DJ8/ECC88.

I started out with HV = +200V.
R = 100kΩ
C = 0.01μF
R1 = R2 = 1MΩ
f = 16Hz

Then I reduced the HV to +24V.
R = 10kΩ
C = 0.47μF
R1 = R2 = 1MΩ
f = 1Hz

Works ok with LEDs.
Surprisingly, the circuit oscillated with supply voltage as low as 1V, though there is not enough voltage to drive the LED.
The LED was visibly flashing with supply voltage at 5V.

 

Mr Chips, thanks for your report. It's good to know that the circuit works at low voltages. I was using a 24V transformer for the plates, and a 6V transformer for the heaters. I will try using the 6V transformer for both. If it's to dim, I'll try a 12V transformer and will connect the heaters in series. Did you try using bulbs? I ordered some 24V bulbs, since the 220V ones I have won't work with the circuit at such low voltages.

 

Mr Chips, thanks for your report. It's good to know that the circuit works at low voltages. I was using a 24V transformer for the plates, and a 6V transformer for the heaters. I will try using the 6V transformer for both. If it's to dim, I'll try a 12V transformer and will connect the heaters in series. Did you try using bulbs? I ordered some 24V bulbs, since the 220V ones I have won't work with the circuit at such low voltages.

No point in using bulbs. There is not enough current through the tubes to light up bulbs unless it is a 2mA @ 1.5V bulb.
Think current, not voltage.
With 24V into 10kΩ the most you will get is 2mA.

Buena Suerte!

 

I finished my project. Thanks everyone!



PS. I added two pots to individually change the frequency of each LED. The knobs can be seen in the third picture.