I put a camera flash power supply to the test. I only had a used 9volt battery with a voltage of 8.67DC. The output was 322vdc! Wow! Now, what circuit could I use with this power supply for a tube based pedal?
Any suggestions, anyone?
Thanks!
Arn C.
[Power To The People!][/quote]
thats cool...
A flash camera supply charges up to a high voltage over some tens of seconds, then discharges all the stored energy through the flash bulb very quickly.
I think you will find that although the voltage is high, the continuous current (and power) available from one of these when connected to a steady state load is quite small.
Quote from: acromartyA flash camera supply charges up to a high voltage over some tens of seconds, then discharges all the stored energy through the flash bulb very quickly.
I think you will find that although the voltage is high, the continuous current (and power) available from one of these when connected to a steady state load is quite small.
I remember discussing this over at the old forum (I think). Here's an article I found on disposable camera flash power supplies:
http://isaac.exploratorium.edu/~pauld/activities/camera_electronics.html
Note there's a step-up transformer that increases the voltage to the 10KV range. In this case the current would be pretty miniscule, but the voltage is way too high for tube stufff anyway. We're more interested in the "first stage" which produces around 300v or so. I thought I remember from the previous discussion that it looked like this might be good for 1-2ma (??). That would be plenty for a simple 1 tube preamp circut. And if you needed more, the camera electronics is small enough that you could use another camera pwr supply in parallel.
Where I got stuck on this idea was that you would still need wall power and some sort of transformer and/or rectifier (could be a wall-wart) for the tube heaters anyway. So the "battery powered" aspect doesn't buy you much in this case. It does simplify the high-voltage power source though. And it keeps it small, which is nice for a pedal.
Doug
I took the measurement without pressing the flash button, Is that where the 1KV power surge comes from?
So, I can hook up several of these in parallel. How many would I need to use with a preamp tube? They are free at CVS drugstore, just have to ask and also you get a AA battery. I would use a 12 dc wallwart to power the pedal.
Arn C.
you save a lot of transformer space (50/60Hz) as well as capacitor bulkiness, but the converter`s frequency might squeal through an exciting
coil in an audible frequency into the circuit (when I remember well, old cameras had a wolf`s howl coming right from the case after flashing - and that was just mechanical howl through resonances...).
For the rest: a cool P.S. for a one-tuber...
//www.puretube.com
Next fun experiment: repeatedly charge and discharge an electronic flashgun right next to an AM radio (between stations) and listen to the sound effects...
I noticed that it only squeals when you first apply power to it(can barely hear it, so high pitched). The squeal dissappears almost immediately. And you do not have to fire the flash. The 300+volts is always there.
Arn C.
...always there as long you don`t load (discharge) it.
As soon as you got your 1mA tube-plate-current hanging in there,
I`m afraid it will keep "working"...
//www.puretube.com
The input to the inverter tramsistor in the flash circuit is designed for 1.5v so you need to limit the input voltage to a lower value than your power adapter is supplying. Otherwise there is a possibility of the mini transformer having to dissipate too much wattage and then burn out.
At 1.5v you will probably get 150v to 160v on the output of the stepup transformer, which can supply several ma.
My son works in a photolab and I have a pile of these cameras for testing.
regards, Jack
Thanks Jack, I will try it with less voltage and I will tie 3 in parallel. I plan on building a little preamp or overdrive tube pedal with this. Does anyone know what tube I could use that won't drain so much?
Thanks!
Arn C.
try a 12ax7 with both plate-Resistors 180 to 330 Kohm,
cathode-R 1.5 to 3.9 Kohm. Grid-R 1Mohm.
Be sure you use at least 250V, better 400 or 630V plate-output caps!!
take care:watch your fingers and have fun
I tried a AA 1.5v battery and couldn't get it to charge up or output any voltage. But with a 9v battery it does,...huh? I even tried pressing the flash button, nada.... I will experiment a bit more...
Arn C.
hey arn any more luck with the camera circuit.???
The only use that I've seen them for is as a tazer, you know the thing that some security people wear to shock rioters into submission.
Ansil,
I have done nothing more with this. Need more people to figure this out.
Thanks!
Arn C.
ahh i will go by the photomat and get some and see what i can do then
Below is a photo of a Kodak Fun Flash 35 circuit board.
At the top left is the flash tube... the light output is on the other side.
Below the flash tube is a square yellowish-silver capacitor marked 222 (0.002uF). Right below the capacitor is a green blob which is the top of the trigger transformer. There is a surface mount resistor marked 502 in this same area but on the other side of the board.
At the top right is a red LED that indicates when the flash is charged. To its left is the black step-up transformer and immediately below them is the oscillator transistor. At the bottom right of the board is the high voltage power supply capacitor.
The circular looking pad in the center of the board to the right of the jumper wire is a touch switch on the other side of the board. It is depressed to start the oscillator working and the capacitor charging. It only takes a few seconds for the LED to come on indicating that the capacitor is fully charged.
The silver bracket extending out of frame by the capacitor is one of the switch contacts. The other is that bracket up by the transistor. When you short these two metal parts together the flash will fire.
This circuit is powered by a 1.5v battery and is quite simple. I haven't measured the voltage yet but let me tell you... when the capacitor is charged, it has quite a bite! I got a finger in the wrong place and jerked back so hard I wrenched my shoulder!!!!
I'm working on converting this into a power supply circuit.
regards, Jack
(http://209.124.248.167/misc/flash01.jpg)
cool jack i am waiting on mine as i just started a new project but i did manage to get some of those disposable cameras
I've updated the photo to show the relevant parts... there are two metal brackets for the battery as indicated by +/-1.5 volt labels. The brackets are easily removed if you want to put in wires connecting to a power suppy.
The two contacts on the right edge of the board can be desoldered and removed. They are used in the original to fire the flash.
The high voltage power for your tube circuit can be taken from the pcb traces connected to the large capacitor. I plan on drilling holes through the board so that I can put wires to carry the power.
There are two white dots connected by a white line in the middle of the board. This shows where the contacts of the mini-switch have to shorted out to make the oscillator run continuously. A simple wire jumper on the opposite side of the board will do fine.
I plan on taking some readings on this power supply tonight to get an idea of how much power it can provide for a tube circuit.
regards, Jack
Here is the flash board after I've prepared it for use as a tube power supply. I have removed the green insulation on the two tracks from the high voltage filter capacitor, drilled holes in the board and tinned around them.
The battery brackets are removed and I have indicated where to connect the plus and minus ends of the battery or power supply.
At the center of the board, I have peeled off the flex switch, which seemed to be mounted only with sticky tape and soldered a short jumper across the contacts so the power supply will run continuously.
(http://209.124.248.167/misc/flash03.jpg)
regards, Jack