What, was this in a newspaper or something? More people paying attention, wow! 
Goals re: features:
Simultaneous display of Vbe Ic and Ib
Switchable current ranges for Ic
Adjustable current for Ib (currently 2 ranges)
Test NPN, PNP and N & Pch. FETs
DC testing
AC testing looking like it will make the list thanks to the recent blessing of a free O'scope (thanks, God)
Protection for the panel meters is intended to be limited by the voltage of the supply... about 12V is all it will have to give, which with the current resistors is safe for a 1.99 (or 1.999) volt meter. That is a good point though. Perhaps the circuit just got a bit more complicated, I'll have to think about it some. Currently, there are some low-noise buffers planned to isolate the test from the meters. Clamping the output shouldn't be too hard.
As for selecting Vce, it sort-of just happens with this design and I'm hard-pressed to think why I would want to monitor it, seeing it's to be a direct relationship with the Ic reading.
peranders, jackinnj has it right with my motivations for building this unit.... DIYAudio is the name of the board... matched components baby. You do raise a different point tangentially: This is not going to be a tester to determine what a device is, as I don't plan on using unknown devices in my DIY Audio kit. Datasheets only get you so far. Then we need some actual numbers
Thanks guys, keep it coming. Jackinnj I'll have to peruse that article after work.
Goals re: features:
Simultaneous display of Vbe Ic and Ib
Switchable current ranges for Ic
Adjustable current for Ib (currently 2 ranges)
Test NPN, PNP and N & Pch. FETs
DC testing
AC testing looking like it will make the list thanks to the recent blessing of a free O'scope
(thanks, God)Protection for the panel meters is intended to be limited by the voltage of the supply... about 12V is all it will have to give, which with the current resistors is safe for a 1.99 (or 1.999) volt meter. That is a good point though. Perhaps the circuit just got a bit more complicated, I'll have to think about it some. Currently, there are some low-noise buffers planned to isolate the test from the meters. Clamping the output shouldn't be too hard.
As for selecting Vce, it sort-of just happens with this design and I'm hard-pressed to think why I would want to monitor it, seeing it's to be a direct relationship with the Ic reading.
peranders, jackinnj has it right with my motivations for building this unit.... DIYAudio is the name of the board... matched components baby. You do raise a different point tangentially: This is not going to be a tester to determine what a device is, as I don't plan on using unknown devices in my DIY Audio kit. Datasheets only get you so far. Then we need some actual numbers
Thanks guys, keep it coming. Jackinnj I'll have to peruse that article after work.
If you have made a good design no part have to be matched, possible the input stage. When you design you use worst case values of critical parameters. If the Hfe is 300 typical and min 150 you take 50-100 as a working value.Stocker said:
If you of some reason do want to match do it in the real stage. Mount a socket and change only one transistor. Note the offset (or whatever) on each transistor. Two transistors with the same offset are probably alike. Building a real transistor tester is a massive overkill. I had a curve tracer long time ago. It was very neat but it was more for checking possible broken transistors.
To each his own. Perhaps Pass would have a thing to say about optimal designs not requiring matched devices? There are several amplifiers I would like to build that require matching for low DC offset at the very least. Besides, aside from the effort, why *not* build it? It has already been a learning experience.
Hi,
Peranders,
your worst case is only considering lowest gain.
For some performance specs, a worst case would be when one Q is lowest gain and the other Q is highest gain.
The spread in parameters is the problem.
Stocker,
if you see a performance improvement by matching transistors come back and report your results. I suspect it will mirror the results achieved by many others.
As an aside D. Self published measured voltages and estimated currents on an LTP front end with almost matching transistors. He particularly drew our attention to input bias current and input offset and how it flowed to the output, but could not be corrected by NFB
Peranders,
your worst case is only considering lowest gain.
For some performance specs, a worst case would be when one Q is lowest gain and the other Q is highest gain.
The spread in parameters is the problem.
Stocker,
if you see a performance improvement by matching transistors come back and report your results. I suspect it will mirror the results achieved by many others.
As an aside D. Self published measured voltages and estimated currents on an LTP front end with almost matching transistors. He particularly drew our attention to input bias current and input offset and how it flowed to the output, but could not be corrected by NFB
Thanks for the encouragement guys. I stayed up and did some calculating last night; hopefully I will complete this thing within the year (note, this is the 2nd year of 'construction'! )
As for improvements, I am hoping there will be none: I aim to build my stuff one time (ha, as if it were possible) and build it as well as I can that once. You all may note from paragraph one of this post that I like to take my time... hopefully this contributes to the best result possible!
Thanks,
David
As for improvements, I am hoping there will be none: I aim to build my stuff one time (ha, as if it were possible) and build it as well as I can that once. You all may note from paragraph one of this post that I like to take my time... hopefully this contributes to the best result possible!
Thanks,
David
here's the Tester using the Measurement Computing USB-1208FS -- on a protoboard -- an LM317 was used to set collector current to 10mA -- for BJT's values of R can be adjusted between output and adjust to set the current from 100uA to 1A -- with the drop-down list. Sorry, I haven't yet completed the MU test for FETs.
I reworked the graphical user interface to be a lot simpler -- just press the button to switch between FET or BJT -- anyone who purchases one of these MCC devices and would like the code just send an email and I'll send a zip file back.
I reworked the graphical user interface to be a lot simpler -- just press the button to switch between FET or BJT -- anyone who purchases one of these MCC devices and would like the code just send an email and I'll send a zip file back.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Ah well, since you're watching, I'll update.
I have been pondering numbers and I am -->.<-- this close to putting parts together. I just need a few clear hours at a stretch with nothing else to do...with a job, wife, kids, dogs, house etc. you can see the hours are few/far between. I have been making slow progress though. The 3rd panel meter has been modified to fit the chassis. The wiring needs to be ironed out. I need to select the actual switches that I will use. I will make a temporary final schematic and wire up a test to see if the circuit is valid.
Big Brother is watching also.
Hello, Echelon.
I have been pondering numbers and I am -->.<-- this close to putting parts together. I just need a few clear hours at a stretch with nothing else to do...with a job, wife, kids, dogs, house etc. you can see the hours are few/far between. I have been making slow progress though. The 3rd panel meter has been modified to fit the chassis. The wiring needs to be ironed out. I need to select the actual switches that I will use. I will make a temporary final schematic and wire up a test to see if the circuit is valid.
Big Brother is watching also.
Hello, Echelon.
For those who care, here is another update. Next thing you know I will be a blogger...
I did the research I was needing for the switches and found out that I can use the nice small switches for the range selectors as long as they are not switched during high-current testing... no problem. I also impressed my wife (a little) twice. once by showing her how after I moved the internal stops, one switch is now 2p2t instead of 2p4t. Once by making the second transformer buzz when I energized it (heavy secondary wires).
I did some work for mounting the third meter, selected a switch for push-to-test (big, red, pokes out the side of the case) and selected a filter capacitor that is pretty hefty for high-current testing, but fits nicely between the transformers.
Still need to mount the sense resistors' PCB, mount the third meter finally, wire up the power supplies, wire in the switches, etc. Testing a few transistors will be the final way to decide what ranges and resistors I'll be using.
More to follow...
I did the research I was needing for the switches and found out that I can use the nice small switches for the range selectors as long as they are not switched during high-current testing... no problem. I also impressed my wife (a little) twice. once by showing her how after I moved the internal stops, one switch is now 2p2t instead of 2p4t. Once by making the second transformer buzz when I energized it (heavy secondary wires).
I did some work for mounting the third meter, selected a switch for push-to-test (big, red, pokes out the side of the case) and selected a filter capacitor that is pretty hefty for high-current testing, but fits nicely between the transformers.
Still need to mount the sense resistors' PCB, mount the third meter finally, wire up the power supplies, wire in the switches, etc. Testing a few transistors will be the final way to decide what ranges and resistors I'll be using.
More to follow...
I did not forget the suggestion of a regulated-temperature heatsink that was raised earlier. I have options for 75 and 45 degrees C and that all day long. Clamp a bar-clamp on a row of devices and let them soak for a few minutes, test them one after another. Sockets seem like a good idea.
Anyway, I took some time to play in the shop today. The DUT power supply is almost all wired up. Switches have begun to be wired and mounted. Mounted a bridge rectifier, made a bracket and mounted the capacitor as well. Redid the resistor board with 0.1% resistors where I could. Tidied up the internal wiring a bit. I so need to get a digital camera.
I also had an idea that seems great to me. I was going to have a switch to kill the capacitor to get some sort of AC test capability... But then I thought, why not have a jack to inject AC into the signal for the base voltage? like, say, from a function generator? Likely never to be used, but wouldnt' it be neat to be able to test the inputs for a sub amp at low frequency and for the highs amps at high frequency? Hmm...
With built-in BNC for the oscilloscope probes...
and a big D-sub for the voltage-outs incase I ever do get a data card for a computer interface...
/edit:
borrowing: Not so much.
I figure, a hundred dollar deposit to come and use it at my place with me watching like a hawk over your shoulder...
But seriously, a small side-business in matching transistors may be in the seminal stages right now.
Anyway, I took some time to play in the shop today. The DUT power supply is almost all wired up. Switches have begun to be wired and mounted. Mounted a bridge rectifier, made a bracket and mounted the capacitor as well. Redid the resistor board with 0.1% resistors where I could. Tidied up the internal wiring a bit. I so need to get a digital camera.
I also had an idea that seems great to me. I was going to have a switch to kill the capacitor to get some sort of AC test capability... But then I thought, why not have a jack to inject AC into the signal for the base voltage? like, say, from a function generator? Likely never to be used, but wouldnt' it be neat to be able to test the inputs for a sub amp at low frequency and for the highs amps at high frequency? Hmm...
With built-in BNC for the oscilloscope probes...
and a big D-sub for the voltage-outs incase I ever do get a data card for a computer interface...
/edit:
borrowing: Not so much.
I figure, a hundred dollar deposit to come and use it at my place with me watching like a hawk over your shoulder...
But seriously, a small side-business in matching transistors may be in the seminal stages right now.
Hi Ed,
I do them (and Mosfets) four at at time. I use a couple power supplies, or a data precision 8200 and supply if I have to match mosfets tightly. A temperature meter monitors the heatsink temp. It is a real pain in the butt.
I find that my Heathkit IT-18 provides pretty close bipolar power transistor matches. I've confirmed this at higher collector currents. I believe that low current matching is more important as the emitter resistors force current sharing at higher currents. That's unless the parts are not even close.
-Chris
I do them (and Mosfets) four at at time. I use a couple power supplies, or a data precision 8200 and supply if I have to match mosfets tightly. A temperature meter monitors the heatsink temp. It is a real pain in the butt.
I find that my Heathkit IT-18 provides pretty close bipolar power transistor matches. I've confirmed this at higher collector currents. I believe that low current matching is more important as the emitter resistors force current sharing at higher currents. That's unless the parts are not even close.
-Chris
Another update:
I did yet more work wiring switches in.
One big hold-up on this whole affair is that one of the meters was acting up, but all the parts are known-good. I pulled the meters (two on a perfboard panel) to work on them and thank God I did!
Apparently all the knocking around the shop has not been good for the power supply for the meters...
I plugged the thing in to test the switches and saw a little blue spark in the fuseholder. I didn't see anything wrong, the parts are all exceedingly inexpensive and so I plugged in a 2A fuse instead of the 3/4A fuse that blew. Well one of the wires got hot on that power board and it started to stink after a 3-second check-for-big-shorts-with-the-fuse test. I looked closer and still didn't see any problem. Thankfully for the next power-up I had the component side facing away from me because two of the 3-amp rectifiers blasted off the board and hammered into the top of an old o'scope on the floor. Sparks, fun.
So I dismounted the board and looked REEEEEEAlly close. those diodes were the positive-going half on a bridge rectifier setup. They went to a wire that was broken off a 0.1" contact and short to chassis ground.
Fixed the short, installed a generic 4A monolithic bridge rectifier and it was all happy again.
The meter was going wonky because one of the display segments was shorting to ground on the perfboard beside the contact. I think the next project will have actual PCBs because these are point-to-point and took forever and still I get this hassle. Anyway I fixed the short and then both meters worked (yay! ) but showed different voltages off the same voltage source. 
I scratched my head for a minute until I realized that I needed to calibrate the meters. One was good and the other was sitting with its 2Vref. at 1.83V. Tweaked that and they now read the same! w00t!
then I celebrated by playing with a white LED and some lithium batteries and called it a night.
/edit: can't type straight.
I did yet more work wiring switches in.
One big hold-up on this whole affair is that one of the meters was acting up, but all the parts are known-good. I pulled the meters (two on a perfboard panel) to work on them and thank God I did!
Apparently all the knocking around the shop has not been good for the power supply for the meters...
I plugged the thing in to test the switches and saw a little blue spark in the fuseholder. I didn't see anything wrong, the parts are all exceedingly inexpensive and so I plugged in a 2A fuse instead of the 3/4A fuse that blew. Well one of the wires got hot on that power board and it started to stink after a 3-second check-for-big-shorts-with-the-fuse test. I looked closer and still didn't see any problem. Thankfully for the next power-up I had the component side facing away from me because two of the 3-amp rectifiers blasted off the board and hammered into the top of an old o'scope on the floor. Sparks, fun.
So I dismounted the board and looked REEEEEEAlly close. those diodes were the positive-going half on a bridge rectifier setup. They went to a wire that was broken off a 0.1" contact and short to chassis ground.
Fixed the short, installed a generic 4A monolithic bridge rectifier and it was all happy again.
The meter was going wonky because one of the display segments was shorting to ground on the perfboard beside the contact. I think the next project will have actual PCBs because these are point-to-point and took forever and still I get this hassle. Anyway I fixed the short and then both meters worked (yay!
) but showed different voltages off the same voltage source. I scratched my head for a minute until I realized that I needed to calibrate the meters. One was good and the other was sitting with its 2Vref. at 1.83V. Tweaked that and they now read the same! w00t!
then I celebrated by playing with a white LED and some lithium batteries and called it a night.
/edit: can't type straight.
Stockman
If you ever get a data card with digital I/O you can run the base injection from one of the IO ports by toggling a bit and low-pass filtering -- that is -- toggle the bit at 1kHz, post filter with a simple RC filter -- should get something which will look like a sine wave.
You can also modulate the base drive with an analog output port -- just write a little code to augment the signal by sin(x) -- there are elegant ways of doing this (magical sine waves by Don Lancaster describes how) -- but there are also cheap and quick ones which work.
Jack
If you ever get a data card with digital I/O you can run the base injection from one of the IO ports by toggling a bit and low-pass filtering -- that is -- toggle the bit at 1kHz, post filter with a simple RC filter -- should get something which will look like a sine wave.
You can also modulate the base drive with an analog output port -- just write a little code to augment the signal by sin(x) -- there are elegant ways of doing this (magical sine waves by Don Lancaster describes how) -- but there are also cheap and quick ones which work.
Jack
I am thinking of having a switch position that will leave the base/gate drive open, that digital drive idea will make a nice auxilliary input for the distant future. Maybe a few projects from now I will be asking for input on a digital I/O DIY PC card...
First I have to get this thing built!
Made some progress on that last night. Mounted the third meter, fabricated brackets for its display. Wired it in. Troubleshot the noisy ground, got it down to 0.4mV, I think I can get that lower. With the input shorted to the ground pin on the meter it reads 0000, which is my target
The power supply for the meters is a standalone PCB with 5, 15, -15 volt regulated supplies neatly laid out; last night I started to include an LED 'on' indicator for each of the regualted outputs.
Still need to wire in the switches, can't do that until I know where they will go and for that I need the top/front cover and the switches mounted. For that I need the cover material which I need to get, but it will be free I am pretty sure. There is going to be some heat dissipation going on inside this thing so the biggest cover/chassis panels are to be perforated.
Oh yes, and please call me
David
(stockman is a bit close to home... I handle all the North American service parts ordering and most of the inventory management for my part of the company. )
First I have to get this thing built!
Made some progress on that last night. Mounted the third meter, fabricated brackets for its display. Wired it in. Troubleshot the noisy ground, got it down to 0.4mV, I think I can get that lower. With the input shorted to the ground pin on the meter it reads 0000, which is my target
The power supply for the meters is a standalone PCB with 5, 15, -15 volt regulated supplies neatly laid out; last night I started to include an LED 'on' indicator for each of the regualted outputs.
Still need to wire in the switches, can't do that until I know where they will go and for that I need the top/front cover and the switches mounted. For that I need the cover material which I need to get, but it will be free I am pretty sure. There is going to be some heat dissipation going on inside this thing so the biggest cover/chassis panels are to be perforated.
Oh yes, and please call me
David
(stockman is a bit close to home... I handle all the North American service parts ordering and most of the inventory management for my part of the company. )
More work...
Wired up the power supply indicators with some dim (3mA) red LEDs for each rail... +5V takes about a minute to go out after switch-off!
Final-mounted the display for the third meter
Laid out wires for some switches, selected red filters for the meters, started thinking seriously about layout on the front panel.
An engineer said to consider a series potentiometer for a coarse adjustment/fine adjustment thing. Sounds good to me except for having to pay for more pots! Ho well. "Nothing in haste, nothing ill done." who used to say that?
Something that just started to bother me: Some of the signal lines are going to be nearly a foot long (or more! ) and possibly in the near vicinity of some large amount of magnetic flux from the transformers... I guess I'll jump off that bridge when I get to it.
Wired up the power supply indicators with some dim (3mA) red LEDs for each rail... +5V takes about a minute to go out after switch-off!
Final-mounted the display for the third meter
Laid out wires for some switches, selected red filters for the meters, started thinking seriously about layout on the front panel.
An engineer said to consider a series potentiometer for a coarse adjustment/fine adjustment thing. Sounds good to me except for having to pay for more pots! Ho well. "Nothing in haste, nothing ill done." who used to say that?
Something that just started to bother me: Some of the signal lines are going to be nearly a foot long (or more! ) and possibly in the near vicinity of some large amount of magnetic flux from the transformers... I guess I'll jump off that bridge when I get to it.
I have cut the front panel so that the meters' displays poke through, it's starting to look like something! I made a tentative layout of the switches and pots on the top, now I need to get to making an actual test measurement to decide some final values and then this has about 3 hours' work left to go once the potentiometers arrive
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