Hi guys!
I'm a newbie so I hope you have a bit of patience with me!
I've to measure the amperage of a tranformer.
I've this multimeter:
all-sun: DM830 GS marking, DIGITAL MULTIMETER
Can I use it to measure the amperage value of the transformer that you can see in the picture below?
I apologize for my ignorance, I hope you can help me!
Thank you so much!
Best regards!😉
I'm a newbie so I hope you have a bit of patience with me!
I've to measure the amperage of a tranformer.
I've this multimeter:
all-sun: DM830 GS marking, DIGITAL MULTIMETER
Can I use it to measure the amperage value of the transformer that you can see in the picture below?
I apologize for my ignorance, I hope you can help me!
Thank you so much!
Best regards!😉
Attachments
You can measure voltage using the Vac voltmeter settings.
The current varies with the load. You can only get sensible current readings if you have an accurate load that exactly matches the rated loading of the transformer.
But don't try to measure current.
Attach the known resistance and measure the voltage across it. That gives you the current without interrupting the flow.
The current varies with the load. You can only get sensible current readings if you have an accurate load that exactly matches the rated loading of the transformer.
But don't try to measure current.
Attach the known resistance and measure the voltage across it. That gives you the current without interrupting the flow.
There is one method that you can use to estimate the current capability of the secondaries.
It relies on the fact that most transformers regulate within approx. 10-15% through their current range.
You need a pile of large resistors.
1. Measure the no-load voltage of the secondary.
2. Keep adding load resistors until the voltage is seen to drop by 10%.
3. Use Ohm's law to detrermine the current when the voltage is seen to drop by this 10%.
This is by no means absolute but it is useful if you have no idea what the secondary current is.
If you have multiple secondarys you have to do all of them simultaneously.
It relies on the fact that most transformers regulate within approx. 10-15% through their current range.
You need a pile of large resistors.
1. Measure the no-load voltage of the secondary.
2. Keep adding load resistors until the voltage is seen to drop by 10%.
3. Use Ohm's law to detrermine the current when the voltage is seen to drop by this 10%.
This is by no means absolute but it is useful if you have no idea what the secondary current is.
If you have multiple secondarys you have to do all of them simultaneously.
10% is not a typical value for a toroid transformer regulation.
Some are as low as 4% and some are as high as 30%.
Do not test to 10% drop. That could severely overload the transformer leading to internal damage that cannot be repaired.
No the 'amperage' or current inputs of your DMM is for DC only. Transformers only work with AC.
In-circuit current measurement is for advanced users. Best to calculate the current from the measured voltage across a known resistance I= V/R. Clamp-on AC current meters are safer and much user friendly, but the common instruments often don't have the lower resolution for hobbyist work.
You probably want to estimate the power or VA of your transformer?
Post weight and dimensions along with each windings open circuit AC voltage and DC resistance. More windings and taps mean more uncertainty with guessing so we must determine internal wire thickness too.
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Thank you very much, dear friends for the replies!😉
Before proceeding, please, let me explain the real situation to you
Actually, I'm asking you the question about the amperage because I've to buy a new trasformer (trafo) in order to replace the old one that you see in the picture, above.
In fact (unfortunately) I don't own that original tranformer anymore (I gave it to friend, thinking I didn't use my old amplifier anymore😡😡😡).
Now I've regretted throwing away that transformer and I'd like so much to get my old amplifier back on track.
So, in order to get it, I've to buy a new transformer for the amp.
For this reason...I ask you this important question:how many ampere should a trasformer have to feed excellently a vintage small amplifier with these features?:
-25 watt RMS at 4 ohm/ 40 watt MAX at 4 ohm
-2 analogic vu-meters with 2 lamps
-pre-phono RIIA (it needs 15 volt)
-1 lamp to indicate that the amplifier is on.
-absorbed power by the amplifier: 100 VA
-secondary output of the transformer: 16,5-0-16,5 volt
You can see the amp section in the pictures below.
A part of the amp section, the 3 little lamps, the pre-phono RIIA and the vu-meters there're no other active components requiring power supply.
So, I know the new transformer should have the following features:
18-0-18 volt (could 20-0-20 volt be excessive?)
120 VA but, as I already said, I don't know a correct amperage value.
So could you reccommend an optimal amperage value for this amplifier?
Well guys, that's all!
Please help me!🙂😉
Thank you for your precious kindness
Best regards
P.S.: I was forgetting an important detail:
even if I no longer have the original transformer of the amplifier, I asked you how to measure the amperage with a multimeter, because the friend to whom I gave the transformer could do it.
However, I think it is too difficult also for him and, for this reason, I prefer to follow your advices.
Before proceeding, please, let me explain the real situation to you
Actually, I'm asking you the question about the amperage because I've to buy a new trasformer (trafo) in order to replace the old one that you see in the picture, above.
In fact (unfortunately) I don't own that original tranformer anymore (I gave it to friend, thinking I didn't use my old amplifier anymore😡😡😡).
Now I've regretted throwing away that transformer and I'd like so much to get my old amplifier back on track.
So, in order to get it, I've to buy a new transformer for the amp.
For this reason...I ask you this important question:how many ampere should a trasformer have to feed excellently a vintage small amplifier with these features?:
-25 watt RMS at 4 ohm/ 40 watt MAX at 4 ohm
-2 analogic vu-meters with 2 lamps
-pre-phono RIIA (it needs 15 volt)
-1 lamp to indicate that the amplifier is on.
-absorbed power by the amplifier: 100 VA
-secondary output of the transformer: 16,5-0-16,5 volt
You can see the amp section in the pictures below.
A part of the amp section, the 3 little lamps, the pre-phono RIIA and the vu-meters there're no other active components requiring power supply.
So, I know the new transformer should have the following features:
18-0-18 volt (could 20-0-20 volt be excessive?)
120 VA but, as I already said, I don't know a correct amperage value.
So could you reccommend an optimal amperage value for this amplifier?
Well guys, that's all!
Please help me!🙂😉
Thank you for your precious kindness
Best regards
P.S.: I was forgetting an important detail:
even if I no longer have the original transformer of the amplifier, I asked you how to measure the amperage with a multimeter, because the friend to whom I gave the transformer could do it.
However, I think it is too difficult also for him and, for this reason, I prefer to follow your advices.
Attachments
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Since this is a replacement transformer , why don't you contact the OEM for parts availability, schematic and parts list. The number one requirement that the replacement parts should fit in the space allowed. A custom solution may be beyond expensive, and the DIY approach will be at best a hack job with possibly 2 standard parts to get any additional windings for lamps etc. Otherwise Id look at the largest capacitors for the WV DC rating and work it backward for an AC voltage estimate. The size that can fit the old space will determine the VA, or amps. the line fuse rating will be another clue for allowable max power. If you can fit a 100VA part that should be more than enough.
Hi Infinia!
Thank you for your reply, first of all!
Unfortunately it's impossible to find schematic and parts list.
However, I'd like to follow a DIY approach for this project even if it will be an expensive solution.
In fact for me it will be more an up-grade of this amplifier than a simple repair.
I also wanted to tell you that there is a lot of space inside for the insertion of a bigger transformer.
Of course, I'll replace also every capacitor on the circuit board.
With regard to the lamps, I know they're 18 volt lamps.
So what do you reccomend to buy?
Thank you!
Regards
Thank you for your reply, first of all!
Unfortunately it's impossible to find schematic and parts list.
However, I'd like to follow a DIY approach for this project even if it will be an expensive solution.
In fact for me it will be more an up-grade of this amplifier than a simple repair.
I also wanted to tell you that there is a lot of space inside for the insertion of a bigger transformer.
Of course, I'll replace also every capacitor on the circuit board.
With regard to the lamps, I know they're 18 volt lamps.
So what do you reccomend to buy?
Thank you!
Regards
What more do you need to know?
100VA at 33V is 3 Amps. You want 16-0-16 or 32CT at 3 Amps.
This is entirely ample for two 8 Ohm loads. At 4 Ohm stereo it won't work FULL power all day all month without getting hot; this is totally fine for speech/music hi-fi work where the 25W/40W happens less than 1% of the time. Indeed the 40W@4r spec implies the rails sag at that test condition.
You can often rough-guesstimate the current by measuring the winding resistance. However for this part the total secondary resistance is likely under 1 Ohm. Few common ohm-meters will read this properly. Some that seem to do so silently lie.
I'm sorry don't know what vendors are in Europe for transformers. Probably ebay or another member can suggest a reasonable source E.g. low shipping cost.
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This is the way you should have started your enquiry.
And you have given your own answer.
120VA.
That's what you need to order. Do not specify amperes.
Specify primary voltage, secondary voltage, secondary VA and any auxilialry secondaries if required.
230:dual 16.5Vac, 120VA.
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Woooow!!!!😉
You can't imagine how your replies helped me!
I'd like to ask you the explanation of something that annoys me so much:
when I used this amplifier, I noticed that the intensity of the lights behind the two vu-meters were not stable.
The two lamps shine to music and I do not like it at all.
This problem is more evident when I increase the volume of the amplifier.
What could be the cause of this problem?
I don't have deep electronic knowledge, but I had read (I don't remember where) that this problem could depend on the rectifier bridges, because they don't provide enough amperage to the circuit.
In this case, in my amplifier, there are two pairs of rectifier diodes: GP15G.
You can see these 4 diodes in the picture above, between the two big pink capacitors.
Since I have to change all the capacitors on the circuit board, I'd like to replace those rectifier diodes too, using more robust components.
What do you say?
Thank you once again for your irreplaceable support and, of course, for your kindness!😉🙂😉
Best regards
You can't imagine how your replies helped me!
I'd like to ask you the explanation of something that annoys me so much:
when I used this amplifier, I noticed that the intensity of the lights behind the two vu-meters were not stable.
The two lamps shine to music and I do not like it at all.
This problem is more evident when I increase the volume of the amplifier.
What could be the cause of this problem?
I don't have deep electronic knowledge, but I had read (I don't remember where) that this problem could depend on the rectifier bridges, because they don't provide enough amperage to the circuit.
In this case, in my amplifier, there are two pairs of rectifier diodes: GP15G.
You can see these 4 diodes in the picture above, between the two big pink capacitors.
Since I have to change all the capacitors on the circuit board, I'd like to replace those rectifier diodes too, using more robust components.
What do you say?
Thank you once again for your irreplaceable support and, of course, for your kindness!😉🙂😉
Best regards
have you found a transformer? replace it then test.
Hard to say anything w/o schematics, right? You could trace out the wiring on the lamps, I reckon a lot of folks would redesign it for white or blue LEDs.
Most good technicians, are not fond of shotgun parts replacement , you may find you've broken something else not related, then it's difficult to troubleshoot stuff at that point esp. w/o test equipment and schematics.
Hard to say anything w/o schematics, right? You could trace out the wiring on the lamps, I reckon a lot of folks would redesign it for white or blue LEDs.
Most good technicians, are not fond of shotgun parts replacement , you may find you've broken something else not related, then it's difficult to troubleshoot stuff at that point esp. w/o test equipment and schematics.
Hi Infinia!
Thank you for your reply!
I haven't yet found the transformer.
Regarding to the vu-meters question, you're absolutely right...unfortunately, as I alredy said, it's impossible to find the schematic of this amplifier.
The only thing I can say to you is that the whole vu-meters electronic components are on the amp circuit board: in fact if you look at the amp picture (in the previous page) you can notice that, between the two fuses, there's a white connector with five colored cables (yellow/black/ two pink and last one is purple)...those cables from the amp circuit board go straight to the two lamps and vu-meters.
I know that this detail about the vu-meters cables is not a big help...🙁
However, if you have some advice to solve the lamps problem...(even if it quite impossible, I presume)...I'm here waiting for you!😉
Thank you for your interest, Infinia!🙂
Best regards
Thank you for your reply!
I haven't yet found the transformer.
Regarding to the vu-meters question, you're absolutely right...unfortunately, as I alredy said, it's impossible to find the schematic of this amplifier.
The only thing I can say to you is that the whole vu-meters electronic components are on the amp circuit board: in fact if you look at the amp picture (in the previous page) you can notice that, between the two fuses, there's a white connector with five colored cables (yellow/black/ two pink and last one is purple)...those cables from the amp circuit board go straight to the two lamps and vu-meters.
I know that this detail about the vu-meters cables is not a big help...🙁
However, if you have some advice to solve the lamps problem...(even if it quite impossible, I presume)...I'm here waiting for you!😉
Thank you for your interest, Infinia!🙂
Best regards
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