I would like to have a display on my amp that gives me some information about current and voltage in different parts of the amplifier.
Ideally I'd have a small display and a toggle button that changes the display to another readingchannel. Perfect would be
Ch1/2: Voltage 300B tube right/left channel (normally 460Vdc)
Ch3/4: Current 300B tube right/left channel (normally 120mAdc)
Ch5/6: Fixed bias voltage right/left channel (normally -95Vdc)
optional:
Ch7/8: Voltage 5687 tube right/left channel (normally 190Vdc)
Ch9/10: Current 5687B tube right/left channel (normally 15mAdc)
Are there (easy) solutions available that can do this?
Ideally I'd have a small display and a toggle button that changes the display to another readingchannel. Perfect would be
Ch1/2: Voltage 300B tube right/left channel (normally 460Vdc)
Ch3/4: Current 300B tube right/left channel (normally 120mAdc)
Ch5/6: Fixed bias voltage right/left channel (normally -95Vdc)
optional:
Ch7/8: Voltage 5687 tube right/left channel (normally 190Vdc)
Ch9/10: Current 5687B tube right/left channel (normally 15mAdc)
Are there (easy) solutions available that can do this?
Ralph,
Measurement of current or voltage involves using shunt or series resistors.
If you are using a moving coil meter, you need to know its FSD (full scale deflection) and it's resistance. After that, it's just some maths.
The problem you've set is a bit more complicated:
You have asked to be able to measure voltage AND current.
For switching voltage readings, it is recommended to use a "break-before-make" (opening) switch.
For switching current measurements, it is recommended to use a "make-before-break switch (shorting).
So, if you want to use 1 meter and 1 switch, you might have to get a bit clever!
Having laid those points before you, I'll go away and have a think.
zzzzzz
First thought: If you were prepared to accept that the cathode voltage was a true representation of the current through the valve, the problem becomes trivial. A 2-pole n-way b-b-m switch and a handfull of resistors is all you need!
Cheers,
Measurement of current or voltage involves using shunt or series resistors.
If you are using a moving coil meter, you need to know its FSD (full scale deflection) and it's resistance. After that, it's just some maths.
The problem you've set is a bit more complicated:
You have asked to be able to measure voltage AND current.
For switching voltage readings, it is recommended to use a "break-before-make" (opening) switch.
For switching current measurements, it is recommended to use a "make-before-break switch (shorting).
So, if you want to use 1 meter and 1 switch, you might have to get a bit clever!
Having laid those points before you, I'll go away and have a think.
zzzzzz
First thought: If you were prepared to accept that the cathode voltage was a true representation of the current through the valve, the problem becomes trivial. A 2-pole n-way b-b-m switch and a handfull of resistors is all you need!
Cheers,
John,
I see the problem. I found a dual channel LCD Meter http://www.lascarelectronics.com/data/pdf/DPM 702S.pdf that enables you to read current and voltage at the same time. If we use two 5-pole switches, one for current (m-b-b) and one for voltage (b-b-m) it can be done, right? I mean is it safe to operate when the amp is powered on? I have no idea how to wire it correctly but we'll figure that our later.
Ralph
I see the problem. I found a dual channel LCD Meter http://www.lascarelectronics.com/data/pdf/DPM 702S.pdf that enables you to read current and voltage at the same time. If we use two 5-pole switches, one for current (m-b-b) and one for voltage (b-b-m) it can be done, right? I mean is it safe to operate when the amp is powered on? I have no idea how to wire it correctly but we'll figure that our later.
Ralph
Ralph,
At first glance that looks fine. The data sheet even gives you the formulae!
Why don't you have a think about how to implement the voltage switching first (easier), and come back to check it out with the forum before ordering part$. Then do the same for the current.
There's a lot of useful info on the datasheet. I believe that working it out yourself will be better than me doing it for you 😉
Of course I'll help if you get into trouble....but I doubt that!
Cheers,
At first glance that looks fine. The data sheet even gives you the formulae!
Why don't you have a think about how to implement the voltage switching first (easier), and come back to check it out with the forum before ordering part$. Then do the same for the current.
There's a lot of useful info on the datasheet. I believe that working it out yourself will be better than me doing it for you 😉
Of course I'll help if you get into trouble....but I doubt that!
Cheers,
Ummm... if you use make-before-break switches it will short the different parts of your amplifier together when switching... I really think you don't want that.
Something like this image. Add more switch poles and shunts and dividers for more channels. The switch *has* to be break before make and able to stand off the voltages present in the amplifier. This could be a problem. 500VDC is much for a switch.
Something like this image. Add more switch poles and shunts and dividers for more channels. The switch *has* to be break before make and able to stand off the voltages present in the amplifier. This could be a problem. 500VDC is much for a switch.
Attachments
Hi,
Cheers,
Only recommended for switching current, and keeping continuity.
The switch need not switch the full voltage. It could be divided down prior to switching.
Cheers,
dhaen said:
And that would only be needed on the current ranges if the current sense resistor is in the positive rail (which I guess it is). The resistors would have to have good matching though. Or use a pot there too. Or else voltage variations will cause inaccuracies in the current measurment.
For the voltage ranges you don't need any extra dividers as they are already there.
But this still isn't really what the OP wanted... Toggle buttons... Maybe using a couple of relays or analog switch IC's and drive logic 🙂
Danger!
Hi,
HIGH VOLTAGE
I would strongly advise against measuring the current on the +ve side of this circuit. It would mean "floating" the measuring circuitry: meter & meter power supply, up at 500 volts.
Although this is sometimes done with moving-coil meters that are designed for it, a DVM module definately is not.
Current in valve circuits is most often measured by interrupting the cathode supply. The shunt resistor can affect the performance, so is often shorted out by the switch when in "neutral".
Take care,
Hi,
HIGH VOLTAGE I would strongly advise against measuring the current on the +ve side of this circuit. It would mean "floating" the measuring circuitry: meter & meter power supply, up at 500 volts.
Although this is sometimes done with moving-coil meters that are designed for it, a DVM module definately is not.
Current in valve circuits is most often measured by interrupting the cathode supply. The shunt resistor can affect the performance, so is often shorted out by the switch when in "neutral".
Take care,
Makes it very complex, too complex for me I think. Maybe in the future I'll look at this again. Thanks!
I think I put you off...
Going back to an earlier post; Since you are using cathode bias, if you measure the cathode voltage, and calibrate the meter to display the corresponding current, it's not complex at all. It only becomes complex if you want to truely measure the current.
Using the above, you could use a 2 pole 5 way break-before-make switch and a handfull of resistors to do it all.
Have another think about it.😉
Cheers,
Ralph,Ralph said:
Going back to an earlier post; Since you are using cathode bias, if you measure the cathode voltage, and calibrate the meter to display the corresponding current, it's not complex at all. It only becomes complex if you want to truely measure the current.
Using the above, you could use a 2 pole 5 way break-before-make switch and a handfull of resistors to do it all.
Have another think about it.😉
Cheers,
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