Test Equipment Sub-Forum

[Richard P]

Has been very handy over the past 34 yrs. to confirm cap leakage at the tested capacitor`s rated working voltage within the tester`s HV testing range.

I didn't think about high voltage cap testing with a power supply since I have a Heathkit C3 that works OK for that, but now that you mention it, my HP 6920B outputs accurate voltages (AC & DC) up to 1000V . . . I'll have to give that a try next time i want to test some caps. The Keithley 196 will pair well with it for microamp current measurement I think.

 

[painttoad]

I know that they rebrand some BK precision equipment, like BK 1655 AC power supply . Maybe they rebranded one of BK's frequency counters?

i will look into that. thank you.

i saw someone online thought it might be rebranded Tabor but i could not find anything.

 

[Bill Ferris]

I didn't think about high voltage cap testing with a power supply since I have a Heathkit C3 that works OK for that, but now that you mention it, my HP 6920B outputs accurate voltages (AC & DC) up to 1000V . . . I'll have to give that a try next time i want to test some caps. The Keithley 196 will pair well with it for microamp current measurement I think.

When I`m at my other bench I occasionally use my Heathkit variable HV bench power supply for some cap impromptu checking/reforming with a 10k 2 watt resistor connected in series that I can measure the voltage across it with my very sensitive Fluke 45 for leakage current.
But the Heathkit HV PS`s max voltage output is around a little over 400 v.

 

[arts]

When I`m at my other bench I occasionally use my Heathkit variable HV bench power supply for some cap impromptu checking/reforming with a 10k 2 watt resistor connected in series that I can measure the voltage across it with my very sensitive Fluke 45 for leakage current.
But the Heathkit HV PS`s max voltage output is around a little over 400 v.

I've often used my bench HV supplies for re-forming caps before installation. No real reason to do this, as they are usually fresh stock. But, somewhere in the sands of time I had once read that this was recommended practice, perhaps as per Nichicon. So long as we don't neglect to install an appropriate series resistor. And verify the rating of every single cap coming out of a bulk pack....Boy, was that loud, smelly and very surprising

 

[Bill Ferris]

I've often used my bench HV supplies for re-forming caps before installation. No real reason to do this, as they are usually fresh stock. But, somewhere in the sands of time I had once read that this was recommended practice, perhaps as per Nichicon. So long as we don't neglect to install an appropriate series resistor. And verify the rating of every single cap coming out of a bulk pack....Boy, was that loud, smelly and very surprising

Undesirable "Party Poppers" with their oily nasty chemical smell and conductive tape spewed all over the area !

 

[arts]

Undesirable "Party Poppers" with their oily nasty chemical smell and conductive tape spewed all over the area !

Does that smell ever linger? Took forever to die out. As my buddy Ron always said, "stupidity should be painful"

 

[fucanay]

I am a very competent paint by numbers restore/recap/repair guy. I am detailed, study tons of threads on AK, research for weeks/months before ordering parts (and their orientations) and turning on my soldering iron (which I am very good with), etc. But what I lack is the ability to work my way around a signal path on a schematic and the ability to probe that path with an oscilloscope. I just don't have that knowledge yet as I am completely self taught from the fine folks on this and other forums.

So, maybe this is the right place for this question. I've been thinking I need to learn some of these skills and I have a project that I believe is suitable, a low powered Pioneer SX-550 receiver with distortion in the right channel. I want to learn where the fault is, not just replace parts until it's fixed. But I am not going to go out and spend hundreds of dollars on equipment I don't know how to use, but I have been thinking of spending the ~$40 on a cheap handheld Oscilloscope from Amazon to learn on. I understand that this isn't up to the standards of some you. The question is, will this cheap scope do the job at all? If so, what would those of you that know a lot more than me recommend that I learn to be able to follow the schematic through the signal path until I find which transistor is causing the distortion.

So I guess this is a multifaceted question. Will that cheap scope do what I need it to and can anyone recommend a resource to learn how to trace an audio signal through a circuit? Specifically through a transistor. Thanks in advance.

 

[painttoad]

can anyone recommend a resource to learn how to trace an audio signal through a circuit?

as an example, look at this schematic, it shows the signal path thru. some schematics do, some don't but once you study a few, it's not hard to figure it out.

Elektrotanya for electronics experts

Electronics forum for electronics experts to repair defective appliance.

elektrotanya.com

 

[arts]

I am a very competent paint by numbers restore/recap/repair guy. I am detailed, study tons of threads on AK, research for weeks/months before ordering parts (and their orientations) and turning on my soldering iron (which I am very good with), etc. But what I lack is the ability to work my way around a signal path on a schematic and the ability to probe that path with an oscilloscope. I just don't have that knowledge yet as I am completely self taught from the fine folks on this and other forums.

So, maybe this is the right place for this question. I've been thinking I need to learn some of these skills and I have a project that I believe is suitable, a low powered Pioneer SX-550 receiver with distortion in the right channel. I want to learn where the fault is, not just replace parts until it's fixed. But I am not going to go out and spend hundreds of dollars on equipment I don't know how to use, but I have been thinking of spending the ~$40 on a cheap handheld Oscilloscope from Amazon to learn on. I understand that this isn't up to the standards of some you. The question is, will this cheap scope do the job at all? If so, what would those of you that know a lot more than me recommend that I learn to be able to follow the schematic through the signal path until I find which transistor is causing the distortion.

So I guess this is a multifaceted question. Will that cheap scope do what I need it to and can anyone recommend a resource to learn how to trace an audio signal through a circuit? Specifically through a transistor. Thanks in advance.

Unless the signal is extremely distorted, generally more than 10%, an oscilloscope will be almost useless for this type of work.

The fastest (and easiest!) way to track down where the distortion is starting is with a signal tracer. And they're usually a lot less expensive than a scope. Just follow the signal through the unit; your ears will pick up lower levels of distortion than a scope ever will.

I still use an ancient Heathkit IT-12 signal tracer. It ain't fancy, high-tech or pretty, but it really is a great tool for this type of work

Interweb pic;

 

[fucanay]

Unless the signal is extremely distorted, generally more than 10%, an oscilloscope will be almost useless for this type of work.

The fastest (and easiest!) way to track down where the distortion is starting is with a signal tracer. And they're usually a lot less expensive than a scope. Just follow the signal through the unit; your ears will pick up lower levels of distortion than a scope ever will.

I still use an ancient Heathkit IT-12 signal tracer. It ain't fancy, high-tech or pretty, but it really is a great tool for this type of work

Interweb pic;

View attachment 3163852

Thanks! That's a whole other piece of gear I don't know anything about. Off to study I go!

as an example, look at this schematic, it shows the signal path thru. some schematics do, some don't but once you study a few, it's not hard to figure it out.

Elektrotanya for electronics experts

Electronics forum for electronics experts to repair defective appliance.

elektrotanya.com

Thanks for that. I've got it downloaded and will be looking at it for a bit.

 

[arts]

But what I lack is the ability to work my way around a signal path on a schematic and the ability to probe that path with an oscilloscope. I just don't have that knowledge yet as I am completely self taught from the fine folks on this and other forums.

Divide and conquer. By looking at the unit and the schematic, you can break things apart into smaller sections, and then analyze each one individually.

What sections do you have in a receiver? Well, you've got a power supply. That's easy, just verify that all of the voltages are there and correct. Done deal.

Then there's the power amp, line-stage preamp (usually with the tone controls and most of the input switching) a phono stage and a tuner. Once you've figured out where the ins and outs are for each of those sections, just listen in at those points in order to localize the problem.

To make things less distracting, run the unit into a dummy load (at a reasonable level) so that all you hear is what you are probing with the signal tracer.

Once you've localized it to a particular section, you can start getting down to the nitty gritty.


EDIT: re signal tracers. They made these for decades, in tube types and solid state models, and in both kit form and ready-made. There are also lots of DIY versions around on the interweb too, if you'd rather roll your own.

 

[fucanay]

Divide and conquer. By looking at the unit and the schematic, you can break things apart into smaller sections, and then analyze each one individually.

What sections do you have in a receiver? Well, you've got a power supply. That's easy, just verify that all of the voltages are there and correct. Done deal.

Then there's the power amp, line-stage preamp (usually with the tone controls and most of the input switching) a phono stage and a tuner. Once you've figured out where the ins and outs are for each of those sections, just listen in at those points in order to localize the problem.

To make things less distracting, run the unit into a dummy load (at a reasonable level) so that all you hear is what you are probing with the signal tracer.

Once you've localized it to a particular section, you can start getting down to the nitty gritty.


EDIT: re signal tracers. They made these for decades, in tube types and solid state models, and in both kit form and ready-made. There are also lots of DIY versions around on the interweb too, if you'd rather roll your own.

That is fantastic. I have been looking at the schematic as a whole and not breaking it into sections. Checking the in and out of each section is a natural starting point and I'm embarrassed that I didn't think of that already. But that's why we should ask questions.

 

[Dana65]

Awesome forum !
It's now my go-to

 

[fucanay]

To make things less distracting, run the unit into a dummy load (at a reasonable level) so that all you hear is what you are probing with the signal tracer.

I've been looking into dummy loads a little as I don't have one. The distortion I'm chasing down starts pretty early on the volume dial. Is it good enough to hook a 100W 8ohm resistor to the speaker outputs, like the ones pictured below?

EDIT: re signal tracers. There are also lots of DIY versions around on the interweb too, if you'd rather roll your own.

I was thinking about building a simple one that uses a small guitar amp for the sound. My understanding is that I need to make a Y cable with a probe on the positive side and a ground alligator clamp on the other side, a high volt capacitor in the middle the cable on the positive side, the end and a guitar jack on the other end.

Like the one in this video:

Does that all sound reasonable? I'm really only doing a couple of smaller amps between 15 and 60 watts and have no interest in getting into the far more complicated monster amps. I know this isn't to the standards of a lot of the people on here and it may make a few cringe, but for some of us, the frequency of use of the tools doesn't justify the features and cost of the professional equipment.

 

[arts]

I've been looking into dummy loads a little as I don't have one. The distortion I'm chasing down starts pretty early on the volume dial. Is it good enough to hook a 100W 8ohm resistor to the speaker outputs, like the ones pictured below?

View attachment 3164186

I was thinking about building a simple one that uses a small guitar amp for the sound. My understanding is that I need to make a Y cable with a probe on the positive side and a ground alligator clamp on the other side, a high volt capacitor in the middle the cable on the positive side, the end and a guitar jack on the other end.

Like the one in this video:

Does that all sound reasonable? I'm really only doing a couple of smaller amps between 15 and 60 watts and have no interest in getting into the far more complicated monster amps. I know this isn't to the standards of a lot of the people on here and it may make a few cringe, but for some of us, the frequency of use of the tools doesn't justify the features and cost of the professional equipment.

Those resistors should be just fine, and shouldn't cost a lot of money.
If you are working on solid state only, you can use a single resistor per channel without fear.
If you are working on tube equipment, you should always use two resistors in parallel, just in case one goes "open". This is because running a tube amp at high levels without a load can cause damage.

Virtually any amplifier can serve as a signal tracer. Using a small guitar amp they way you are describing is a great idea, and and can save you some bucks if you already have one. But (and there's always a "but") most guitar amps have a LOT of gain occurring BEFORE the volume control, so it can be very easy to overload the input stage if you try feeding line-level signals into a pickup-level input stage. You may have to pad the input level from the probe to prevent distortion. You could even wire in a pot (after the capacitor!) to have a variable input level.

Don't worry about the standards of other people. And thankfully, there aren't too many jugheads like that on AK. Quite frankly, you don't need a thousand buck temperature-controlled soldering station or a test bench that looks like (or costs as much as..) the NASA remote control for the space shuttle. I'll take a smart guy who can learn, innovate and overcome over some mook with a fat wallet every day of the week

 

[fucanay]

Those resistors should be just fine, and shouldn't cost a lot of money.
If you are working on solid state only, you can use a single resistor per channel without fear.
If you are working on tube equipment, you should always use two resistors in parallel, just in case one goes "open". This is because running a tube amp at high levels without a load can cause damage.

Virtually any amplifier can serve as a signal tracer. Using a small guitar amp they way you are describing is a great idea, and and can save you some bucks if you already have one. But (and there's always a "but") most guitar amps have a LOT of gain occurring BEFORE the volume control, so it can be very easy to overload the input stage if you try feeding line-level signals into a pickup-level input stage. You may have to pad the input level from the probe to prevent distortion. You could even wire in a pot (after the capacitor!) to have a variable input level.

Don't worry about the standards of other people. And thankfully, there aren't too many jugheads like that on AK. Quite frankly, you don't need a thousand buck temperature-controlled soldering station or a test bench that looks like (or costs as much as..) the NASA remote control for the space shuttle. I'll take a smart guy who can learn, innovate and overcome over some mook with a fat wallet every day of the week

Thanks a ton. I'll look into adding a pad to the probe I build to get the signal down a little. I do have a Radial ReAmp box which is a passive transformer line level to guitar level converter. Maybe I should use an XLR cable instead of the guitar cable and just use this to lower the signal to the right level. Does that seem right? Is there anything in that boxes specs that make this a bad idea?

This exchange helps me greatly and hopefully some other people that come along in the future that don't have big bucks to spend on the equipment either. In an earlier time in my life I amassed quite a lot of musical instrument gear, so the guitar amp and reamp box I just happen to have here already.

 

[arts]

I would skip the ReAmp. It's not designed to do what you need to do. Just go with the modified guitar cable probe.

"In an earlier time in my life I amassed quite a lot of musical instrument gear"
Oh lord, I collected enough equipment to backline most world tours, but have begun thinning the herd for a few years now. For vintage Ampeg's, I'm almost down to a dozen

 

[Cubdriver]

I've been looking into dummy loads a little as I don't have one. The distortion I'm chasing down starts pretty early on the volume dial. Is it good enough to hook a 100W 8ohm resistor to the speaker outputs, like the ones pictured below?

View attachment 3164186

A very important thing to keep in mind regarding those power resistors that I haven’t seen mentioned in these past few posts is that to dissipate their full rated power they MUST BE on a heat sink - that’s the purpose of the flat flanges with the mounting holes. If there’s no data sheet available for them to clarify the requirements, I’d suggest looking up similar ones on Digi Key or Mouser and looking at their data sheets - they should get you close enough for horseshoes and hand grenades. Without heat sinking, their power handling abilities will be much less.

-Pat

 

[Cubdriver]

As a for instance, this should get you to a data sheet for a similar model from Ohmite - note that without a heat sink, the power handling drops from 100 W to 30 W.

Ohmite HS100 8R F resistor data sheet

-Pat

 

[fucanay]

A very important thing to keep in mind regarding those power resistors that I haven’t seen mentioned in these past few posts is that to dissipate their full rated power they MUST BE on a heat sink - that’s the purpose of the flat flanges with the mounting holes. If there’s no data sheet available for them to clarify the requirements, I’d suggest looking up similar ones on Digi Key or Mouser and looking at their data sheets - they should get you close enough for horseshoes and hand grenades. Without heat sinking, their power handling abilities will be much less.

-Pat

I will definitely mount it to something to help dissipate the heat with some thermal compound, but I’m likely only going to get to maybe 25 watts before I get to the point of distortion. I am never going to get these amps up to full volume during my tests. But that is really good advice for anyone that comes along and reads this in the future for a different application.