Hi @ll,
Some years ago i bought the Safety valve in Version 1.4 unfortunatley it doesn‘t work. Now i want to fix it. First i tried to turn Diods 1 and 2 But there is no change.I didn’t hear something
Haven‘t the original shematics anymore…
What could be the problem?
Hope you could help me here.
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If you apply power to the device you can check the following;
1: is the red wire on the connector on the PCB connected to -12 V?
Counting from the red wire, are the 2nd, 3rd and 4th connected to GND?
Counting from the red wire, is the 5th connected to +12 V?
If any of these are not correct, you need to sort those out before continuing !
2 - does the filament glow (wait for at least 0.5 - 1 minute) in the tube when the module is powered up?
If it does not, whatever else is wired correctly in the circuit, you will not get any output signal.
3 - if you apply power, can you measure any voltage on the diodes? On the side of the power supply you should measure the voltage of the power supply. On the other side, you should measure a voltage that is up to 0.7 volts less.
I do not have a schematic of this version. But given that they are close to the power connecter I assume the diodes are there to protect the circuit from connecting power that has its poles reversed.
Now for your trial: you changed 2 diodes, but what if only one was reversed? It is wise to change only one thing at a time and then assess the situation again.
To me it seems that in the 2nd picture both diodes are connected the wrong way around. But the picture is not very clear I’m afraid.
You can assume the following: the silver band of the diode should always be connected to the point with the lowest voltage of the 2 points you are supposed to connect it to to be able to conduct current. Check whether that is the case in your circuit.
If the diodes are there only for reverse pole protection, to test the circuit you could temporarily bridge them with some wire and see what happens. If the circuit works, then you can one by one remove one of the wires and check whether it keeps on working.
Mind you, it can take up to half a minute or more for the tube to heat up and it to amplify the input signal.
Note, that tubes are very rugged devices in an electrical sense, so you will not easily blow them up. So the last thing to have any doubts about is the tube.
When doing any tests with electronics it can be helpful / insightfull to use a regulated power supply which allows you to turn up the voltage from 0 to the value you want to have. While turning it up slowly keep an eye on a current meter in series with the power line of the device and check that the current is slowly rising to an acceptable value while you turn up the voltage. If the current rises to a high value very quickly, that might point to a short or reversal of polarity somewhere in the circuit. In case of the Safety Valve, which has a filament which will draw quite a bit of current, you can do this once without the valve being inserted in its socket and once with the valve inserted in the socket so that you can assess which current values you may expect to see.
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Hi Jos,
Thank you a lot ….but anyway it doesn‘t work.
I tried to bridge booth diods. Nothing is glowing.
On the IC i have 11.5 V when i meassure against the ground.
I didn‘t hear anything. When i But of the Power i here a Signal for some seconds an it gets less louder. The potis didn‘t change something.
Don‘t want to put it in the waste….
No filament glowing? Maybe the filament is broken or it does not get any power.
1: Try to measure the resistance of the tube between pins 4 and 5. Mine measures about 12 ohm (when cold).
2: when you switch on the device between pins 4 and 5 you should measure a voltage
3: on that part of the power supply the filament is connected to (probably the positive side) it should draw about 140mA at the start and then drop a bit once it heats up. Given the series resistor on the actual filament between pins 4 and 5 there will be a lower voltage of about 9V.
The way the IC is soldered on the PCB in the picture makes that pin 1 is on the bottom right. Is that where is supposed to be? The left top pin is pin 5 and should be an input which should not be 11.5V.
In the early versions of the safety valve on the IC there should be a positive AND a negative voltage. On pin 7 you should measure about 12V and on pin 4 you should measure about -12V. If these voltages are not correct, check that part of the circuitry. Also check that your power supply is providing the right voltages and that it can deliver the
The original published schematic had a TL071 (a single opamp) in it. You are using a TL072 which is a double opamp. That may be correct if your version is a newer version than the one I know. So I think it is wise to ask Sam for a schematic for the PCB you are using (I don’t have one, I made my safety valves on perf boards) and upload it to this thread.
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