A quick tube (valve) fuzz box

[JohnH]

I'm not sure if was Magic Smoke or Idiot Dust that came out the time I tried to test our electric horse fence (7000 volts) with my multimeter...

D'oh!!!

Woah! That is very many volts

[FrankenWashie]

Woah! That is very many volts

One would assume it is very low Amperage? I’d hope?

[McCreed]

One would assume it is very low Amperage? I’d hope?

Yes, that's why it doesn't kill you, but will deliver a helluva a thump. (still kills a multimeter though )

Not one of my brighter moments btw. Not sure what I was thinking...

[Cliff Rogers]

I know about electric guitars but I didn't know there were electric horses.

[jonwhitear]

I think I'm going to have a go at making this pedal - looks like a fun project. Can anyone recommend part numbers for the 40106 (Jaycar have a 74C14 Hex Schmitt Trigger which looks like it should be OK) and the mosfet (Jaycar have a 2N7000 N-Channel FET, but it's only 60V)?

Cheers, Jon.

[JohnH]

Hey Jon,

I thought 74C14 and 40106 were the same, but I haven't looked at the datasheets to confirm:

http://electronica.ugr.es/~amroldan/...05v%20to%2015v.

I'm not sure where you're putting the 2N7000?

[DrNomis_44]

Here's a simple circuit for generating the high voltage needed to run tubes, like the 12AX7/ECC83 etc, properly, it's basically a 60kHz square wave oscillator made from a CD4049, or CD4069 Cmos Hex Inverter IC, two 33k resistors, and a 330pF capacitor, and a voltage multiplier made from five 1N4007 1000V PIV Silicon Power Diodes, and six 33uF/50V electrolytic caps.

Inverters D,E, and F are just used to buffer the output of the 60kHz square wave oscillator, formed by inverters A,B, and C, the two 33k resistors, and 330pF cap, so that it has enough current-output capacity to drive the voltage-multiplier circuit.

I remember doing some breadboard experiments with this circuit, and found that I could increase the output-voltage, simply by adding more 1N4007 diodes and 33uF/50V caps, I was able to easily generate +90V DC from a single 9V battery that I used to power the circuit.

Here's a pic of the circuit for those who are interested in checking it out:




One great thing about this circuit is that you can easily power it off a +15V DC supply, which means that you can then also run the tube heater off a DC supply as well, which will reduce hum.


The only caveat with this circuit is that the working voltage of each of the 33uF caps needs to be at least 50V DC or greater, 33uF/63V caps should work fine, I've used some 1uF/100V caps in the circuit instead of 33uF/50V and they worked fine.


As a side-note, if you build the high voltage power supply circuit as I have posted above, you will get about +45V out of it, to increase the output-voltage you need to add more 1N4007 diodes and 33uF/50V caps.

[jugglindan]

Interesting. I have seen charge pumps using the ICL7660S followed by a similar diode/cap multiplier, but not with the CD4049.

[jonwhitear]

I thought 74C14 and 40106 were the same, but I haven't looked at the datasheets to confirm:

Thanks John.

I'm not sure where you're putting the 2N7000?

DrNomis_44 added it in his modifications, earlier in the thread. I've drawn up the circuit, which shows it.

[jonwhitear]

The only caveat with this circuit is that the working voltage of each of the 33uF caps needs to be at least 50V DC or greater, 33uF/63V caps should work fine, I've used some 1uF/100V caps in the circuit instead of 33uF/50V and they worked fine.

Would there be any changes to the original circuit (with your mods) required with this power supply? I gather the original makes about 70V, whereas this one's about 90V.