Hello,
A fellow member here wants to have some old style meter on his new to build solid state amplifier.
The power supply has a positive and a negative rail voltage of around 18 volts.
I have a few Simpson model 324 new in box in stock ( just the replacement panel meter ) so not the complete unit.
In the photo you can see it can be used in a range from 0-30 volts.
The text on the meter says 1000 ohms per volt.
In the second attachment i copied the information that was given by the shop a few decades ago. ( The box mentions a date February 1964, it is probably NATO stock)
What value resistor to use to get the correct reading for around 18 volts DC, probably will add a pot for fine adjustment.
Can the same meter also be used to indicate the DC value on the negative rail and if so which changes need to be made in the connections??
Greetings, Eduard
P.s the correct answer will be rewarded with a new meter if you are willing to pay the transport.
A fellow member here wants to have some old style meter on his new to build solid state amplifier.
The power supply has a positive and a negative rail voltage of around 18 volts.
I have a few Simpson model 324 new in box in stock ( just the replacement panel meter ) so not the complete unit.
In the photo you can see it can be used in a range from 0-30 volts.
The text on the meter says 1000 ohms per volt.
In the second attachment i copied the information that was given by the shop a few decades ago. ( The box mentions a date February 1964, it is probably NATO stock)
What value resistor to use to get the correct reading for around 18 volts DC, probably will add a pot for fine adjustment.
Can the same meter also be used to indicate the DC value on the negative rail and if so which changes need to be made in the connections??
Greetings, Eduard
P.s the correct answer will be rewarded with a new meter if you are willing to pay the transport.
Attachments
If you want 30 V full scale, you will need a resistor of 30 kohm (or more accurately 30 kohm minus the resistance of the meter itself). When you connect the positive side of the series connection of the resistor and meter to ground and the negative side to the negative rail, you measure the negative rail voltage. Add a break-before-make double-pole double-throw switch and you can switch between the rails.
1000 ohms per volt meter means on the 3 volt scale its input resistance is 3000 ohms for a full scale reading of 3 volts.
30K for 30 volt scale and 300K for 300 volt scale and 600K for the 600 volt scale
you want 18 Volt full scale then using the 3 volt input and a 15 K resistor should do it. You will have to print a scale on the meter face.
Why not just use the 30 volt scale?
to measure negative rails you will have to put the meter - input on the negative rail and + input on the ground. You will need a double pole double throw switch. A toggle switch with 6 connections.
If you are going to remove the meter from the case, use the resistor that is in the meter for the 30 Volt scale.
When testing the meter always use a large value resistor in series with the meter to measure voltage.
Im guessing but I think the meter is a 1ma movement. ie 1 Volt/1000ohms
30K for 30 volt scale and 300K for 300 volt scale and 600K for the 600 volt scale
you want 18 Volt full scale then using the 3 volt input and a 15 K resistor should do it. You will have to print a scale on the meter face.
Why not just use the 30 volt scale?
to measure negative rails you will have to put the meter - input on the negative rail and + input on the ground. You will need a double pole double throw switch. A toggle switch with 6 connections.
If you are going to remove the meter from the case, use the resistor that is in the meter for the 30 Volt scale.
When testing the meter always use a large value resistor in series with the meter to measure voltage.
Im guessing but I think the meter is a 1ma movement. ie 1 Volt/1000ohms
Hello,
I will read the answer carefully later in the process of cooking.
I meant i wanna use the meter in such a way that with the present dial 18 volt will show as 180 volt.
Should the position of the two resistors be like in the attachment. So both connected on right ( = plus) terminal of the meter.
I have just the panelmeters themselves so i can use one on each side of the power supply.
Depending on the value of the two resistors i could also use a multiturn potmeter in combination with a resistor so must of the drop will be across the resistor. There will not be that much current running i presume.
If any of you interested in a meter just me a message.
Greetings, Eduard
I will read the answer carefully later in the process of cooking.
I meant i wanna use the meter in such a way that with the present dial 18 volt will show as 180 volt.
Should the position of the two resistors be like in the attachment. So both connected on right ( = plus) terminal of the meter.
I have just the panelmeters themselves so i can use one on each side of the power supply.
Depending on the value of the two resistors i could also use a multiturn potmeter in combination with a resistor so must of the drop will be across the resistor. There will not be that much current running i presume.
If any of you interested in a meter just me a message.
Greetings, Eduard
Attachments
Just a thought. If your customer just wants a meter as eye candy, I think most non-technical people would enjoy seeing the needle bounce around to the music. And that would be easy enough to do. Take a sample of the signal path, rectify it and fed it to the meter.
Hello Enzo,
It is not a customer. Just some exploring diy audio. He wants to look the amp a bit like a vintage one . Which means that most meters on ebay that look nice are expensive and are difficult to find a pair. Mine are new in box, manufactured in 1952, send him a picture and told him i asked some info here to see if we can use a pair of them.
Greetings, eduard
It is not a customer. Just some exploring diy audio. He wants to look the amp a bit like a vintage one . Which means that most meters on ebay that look nice are expensive and are difficult to find a pair. Mine are new in box, manufactured in 1952, send him a picture and told him i asked some info here to see if we can use a pair of them.
Greetings, eduard
The meter and the resistor have to be connected in series, but in what order doesn't matter. That is, what you have drawn is fine, but if you had drawn the series resistors on the minus sides, that would have been equally fine.
About 0.6 mA at 18 V, 1 mA at 30 V, so the power dissipation of the resistor will be just below 10.8 mW or 30 mW, respectively. You can use a 27 kohm resistor and a 5 kohm trimmer potmeter if you like.
Hello,
Just done some '' test ''
With a 150 Kohm in series and a 9 volt battery ( did not check the actual voltage) the hand ended up in the middle of the scale.
What i am trying to achieve is a meter that will indicate 100 as the actual voltage is 10 and 200 as the actual voltage is 20.
I know i will have to adjust the 150 K ohm I do have some Bourns 500Kohm multiturn trimpots. Dont know if i have other values so i could '' create ''something with the biggest part of the R value in a resistor and use a lower value trimmer for final adjustment.
Greetings, Eduard
Just done some '' test ''
With a 150 Kohm in series and a 9 volt battery ( did not check the actual voltage) the hand ended up in the middle of the scale.
What i am trying to achieve is a meter that will indicate 100 as the actual voltage is 10 and 200 as the actual voltage is 20.
I know i will have to adjust the 150 K ohm I do have some Bourns 500Kohm multiturn trimpots. Dont know if i have other values so i could '' create ''something with the biggest part of the R value in a resistor and use a lower value trimmer for final adjustment.
Greetings, Eduard
That's strange, because it then has to be an instrument for 120 uA or so rather than 1 mA. The required resistance for 30 V full scale is then about 250 kohm.
Hello Marcel,
With a 240 Kohm resistor:
7.47 volt ( checked) will indicate 90 volt= 9 volts
9,02 volt will indicate 105 volt = 10,5 volts
I double checked with another panelmeter so now we know it has to be around 250Kohm is guess
Could it be that the 1000 ohm per volt is the value to be used for the 600 and 300 volt dial?
The complete clearly shows 0-3 and 0-30 volts too.
Greetings, Eduard
With a 240 Kohm resistor:
7.47 volt ( checked) will indicate 90 volt= 9 volts
9,02 volt will indicate 105 volt = 10,5 volts
I double checked with another panelmeter so now we know it has to be around 250Kohm is guess
Could it be that the 1000 ohm per volt is the value to be used for the 600 and 300 volt dial?
The complete clearly shows 0-3 and 0-30 volts too.
Greetings, Eduard
Specially since real use is eye candy, using it just to measure rail voltage is BORING.
As exciting as watching grass grow.
Fully agree with Enzo about using it as some kind of VU-Meter
An old amp would have used it for that purpose; a voltage meter (if used) would be mounted on the mains distribution panel, or an external regulated/variable power supply, not on the amp itself.
As exciting as watching grass grow.
Fully agree with Enzo about using it as some kind of VU-Meter
An old amp would have used it for that purpose; a voltage meter (if used) would be mounted on the mains distribution panel, or an external regulated/variable power supply, not on the amp itself.
That corresponds to 103.75 uA full-scale, neglecting the instrument's own resistance. You will need about 289.16 kohm to get 30 V full-scale then.
That corresponds to 107.38 uA full-scale, neglecting the instrument's own resistance. You will need about 279.38 kohm to get 30 V full-scale then.
It could, but it is still strange. A meter that draws at most 105 uA or so from the circuit under test affects the circuit less than one that draws a complete milliamp, so why would they have chosen this solution?
I have seen schematics of analogue multimeters that had a trimmable resistor in parallel with the moving-coil meter to fine tune its sensitivity, but the current through the trimmable resistor was then always a small fraction of the current through the moving-coil meter.
By the way, if you like moving-coil meters, you will love this replica of one of the transmitters of the first Dutch broadcaster: Replica Idzerda zender Ed Plevier NVHR - YouTube
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Hello,
I have a Mcintosch mc2505 that indeed looks nice with those meters. Still need some work.
But with these Simpson meters i could be nice to see them moving. NOW they will just show the DC voltage feeding the circuit. A bit boring but let it be.
After the amp has been finished my audio friend in Brazil can still decide to turn them into bouncing meters.
Greetings, Eduard
P.s On my VT25 monotriode amp i used a vintage German meter to indicate the Dc voltage at the first power supply cap and two yamamoto 50 mA to show the current going through the circuit. Both meters dont move except during power switch but it still looks nice.
I have a Mcintosch mc2505 that indeed looks nice with those meters. Still need some work.
But with these Simpson meters i could be nice to see them moving. NOW they will just show the DC voltage feeding the circuit. A bit boring but let it be.
After the amp has been finished my audio friend in Brazil can still decide to turn them into bouncing meters.
Greetings, Eduard
P.s On my VT25 monotriode amp i used a vintage German meter to indicate the Dc voltage at the first power supply cap and two yamamoto 50 mA to show the current going through the circuit. Both meters dont move except during power switch but it still looks nice.
Attachments
Hello,
I have seen a complete meter where there as not a division for volts but for points to be used for checking telephone lines.
If i would adjust the value of the pot in such a way that it will indicate 90 ( 9 volts) when i connect a 9 volt battery. Will the same pot value give a reading of 150 (15 volts) when i connect a 15 volt regulated supply?
I came across these '' transmitters '' but this a different world than the audiophile community.
Greetings, Eduard
I have seen a complete meter where there as not a division for volts but for points to be used for checking telephone lines.
If i would adjust the value of the pot in such a way that it will indicate 90 ( 9 volts) when i connect a 9 volt battery. Will the same pot value give a reading of 150 (15 volts) when i connect a 15 volt regulated supply?
I came across these '' transmitters '' but this a different world than the audiophile community.
Greetings, Eduard
if you have an ohm meter measure the value of the resistor on the 30 volt scale inside your original vintage meter. That is the vale you will most likely need.
Hello,
I only have a number of replacement meters not the complete unit so to say.
@ marcel the scale have both number 324
But with this one the 1000 ohms per volt is missing and according to the you tube video it will indicate up to 100 volts ( points)
Simpsons Ohm & DC Volt Meter Model 324 - YouTube
The ones i have come from old army stock so it could be they were used in a special set up and not just for replacement in the unit pictured in my opening post.
Greetings, Eduard
I only have a number of replacement meters not the complete unit so to say.
@ marcel the scale have both number 324
But with this one the 1000 ohms per volt is missing and according to the you tube video it will indicate up to 100 volts ( points)
Simpsons Ohm & DC Volt Meter Model 324 - YouTube
The ones i have come from old army stock so it could be they were used in a special set up and not just for replacement in the unit pictured in my opening post.
Greetings, Eduard
ok so you dont know the ohms per volt of the meter, no problem. put a large value pot in series with the bare meter, 500K ohms to be safe, set the pot to max resistance. Put a 9 volt battery across the resistor and meter. Warning do NOT connect a battery across the meter alone, always have a large value resistor in series with the meter, in this case its a 500K ohm pot or whatever you have. Put a DVM on current reading is series with the meter and resistor. Slowly adjust the pot till the meter reads full scale. Remove the DVM. Connect the meter to the resistor. Put the DVM on volts. Measure the voltage across the meter when the meter reads full scale. Lets say the meter takes .001 amps and has a 1 volt reading when it reads full scale. If the meter has a 30 volt scale printed on it you will need a 29K ohm resistor in series with the meter so the meter will read properly.
30-1 = 29
29/.001 =29,000
if one of your meters only has a 100 volt scale you will have to print a new label to put over the meter face.
30-1 = 29
29/.001 =29,000
if one of your meters only has a 100 volt scale you will have to print a new label to put over the meter face.