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pointers to transistor (semiconductor) curve tracer circuits/projects

Started by Unknown October 28, 2018
I find myself in a situation where I am repairing some high end audio amps and cassette decks that have house numbered semiconductors, mainly transistors as well as JDEC p/n that are NLA.

I have found a few transistors that are dead and need to be replaced.  Fortunately, they are in parts of the amp where the other channel has an identical transistor.
Having one transistor as a base will allow me to match something close to the original.

I have made (in the past)  the typical transistor curve tracer that shows the curves on a scope - cute but not precise enough for my intentions. I am more interested in a lab type instrument. 

Basically what I am looking for is a curve tracer that has a micro attached to it that have some A/D's on them that can record the data of interest (e.g. Ib (vb), Vce, etc.  
I've considered an arduino based approach but they have the limitations of  5V max on the input for the A/Ds and don't want to scale it.
I've looked for old Heathkit and Tek curve tracers that I could augment with a micro but they seem to be very scarce, in addition to having transistors in them that are NLA.
I could design one myself but in all honesty, I'd prefer to find something where someone has 'plowed the ground' and at the very most, I'd have to augment it with a micro.  Yea, I am a bit lazy - the intent was to fix the amp, not develop a curve tracer....
Thanks in advance
J



On Sun, 28 Oct 2018 17:46:44 -0700 (PDT), jjhudak4@gmail.com wrote:

>I find myself in a situation where I am repairing some high end audio amps and cassette decks that have house numbered semiconductors, mainly transistors as well as JDEC p/n that are NLA. > >I have found a few transistors that are dead and need to be replaced. Fortunately, they are in parts of the amp where the other channel has an identical transistor. >Having one transistor as a base will allow me to match something close to the original. > >I have made (in the past) the typical transistor curve tracer that shows the curves on a scope - cute but not precise enough for my intentions. I am more interested in a lab type instrument. > >Basically what I am looking for is a curve tracer that has a micro attached to it that have some A/D's on them that can record the data of interest (e.g. Ib (vb), Vce, etc. >I've considered an arduino based approach but they have the limitations of 5V max on the input for the A/Ds and don't want to scale it. >I've looked for old Heathkit and Tek curve tracers that I could augment with a micro but they seem to be very scarce, in addition to having transistors in them that are NLA. >I could design one myself but in all honesty, I'd prefer to find something where someone has 'plowed the ground' and at the very most, I'd have to augment it with a micro. Yea, I am a bit lazy - the intent was to fix the amp, not develop a curve tracer.... >Thanks in advance >J > >
Do you generally have schematics? That should be enough to pick a replacement part. A curve tracer tells you nothing about thermal properties, namely power handling capacity. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On 10/28/2018 08:56 PM, John Larkin wrote:
> On Sun, 28 Oct 2018 17:46:44 -0700 (PDT), jjhudak4@gmail.com wrote: > >> I find myself in a situation where I am repairing some high end audio amps and cassette decks that have house numbered semiconductors, mainly transistors as well as JDEC p/n that are NLA. >> >> I have found a few transistors that are dead and need to be replaced. Fortunately, they are in parts of the amp where the other channel has an identical transistor. >> Having one transistor as a base will allow me to match something close to the original. >> >> I have made (in the past) the typical transistor curve tracer that shows the curves on a scope - cute but not precise enough for my intentions. I am more interested in a lab type instrument. >> >> Basically what I am looking for is a curve tracer that has a micro attached to it that have some A/D's on them that can record the data of interest (e.g. Ib (vb), Vce, etc. >> I've considered an arduino based approach but they have the limitations of 5V max on the input for the A/Ds and don't want to scale it. >> I've looked for old Heathkit and Tek curve tracers that I could augment with a micro but they seem to be very scarce, in addition to having transistors in them that are NLA. >> I could design one myself but in all honesty, I'd prefer to find something where someone has 'plowed the ground' and at the very most, I'd have to augment it with a micro. Yea, I am a bit lazy - the intent was to fix the amp, not develop a curve tracer.... >> Thanks in advance >> J >> >> > > Do you generally have schematics? That should be enough to pick a > replacement part. > > A curve tracer tells you nothing about thermal properties, namely > power handling capacity. > >
for "high end" audio amps and cassette decks the parameters you'd also want to know the noise specifications a curve tracer won't tell you that either. But outside of critical sections like phono preamps that were designed for very low noise the exact specifications of small signal transistors in TO-92 package in audio equipment is kinda noncritical, the jellybean transistor they went with in a particular design is often whatever what was on sale at the time. I like the BC550C/BC560C as generic audio small signal transistor replacements
I got a transistor spec book here that goes so old the first number in it is 2A. It doesn't give curves but really, do you need that ? Why would hfe in the linear range be that critical that you can't do it with a decent generator n shit ? Technically you could do it without a scope, and accurately. 

I mean, this "intent to fix the amp", what kind of amp ? An instrumentation amp with about 500VA output designed for varied, nonlinear and and highly reactive loads ? 

The only transistors that are critical like that are those used in a current sharing scheme, especially if they didn't want alot of Re on them. 

If it is analog current sharing then you really just need to match them at somewhere near their maximum current like 70%, that'll make them share when it counts. Who cares when it is operating at 5% output ? I think you are overthinking this, if I am wrong say so, and of course do tell why...

Incidentally, they obviously discontinued that 2A. I don't know how we'll get by. Fifty volts ! 120mW, 8mA !, Icbo 2mA, hfe 3. that means that the Vceo might be as high as hfe times Icbo, 2 X 3. So the operating range could be from 6 - 8 mA collector current...

Hell, 2mA @ 40V ? Umm, 20K ohms ? I mean not really but it seems your source resistance better be lower than that, at least to DC. A transformer ! Now where's that Triad-Utrad book at ? All these damn tubes around. Now look ! The other day I couldn't find an ion trap to save my life. Then kids better keep off my grass or I'll give them an (_|_)full of rock salt outta old betsy here. Shoots just as straight as she did in the war between the states she does.
On 10/28/2018 08:46 PM, jjhudak4@gmail.com wrote:
> I find myself in a situation where I am repairing some high end audio amps and cassette decks that have house numbered semiconductors, mainly transistors as well as JDEC p/n that are NLA. > > I have found a few transistors that are dead and need to be replaced. Fortunately, they are in parts of the amp where the other channel has an identical transistor. > Having one transistor as a base will allow me to match something close to the original. > > I have made (in the past) the typical transistor curve tracer that shows the curves on a scope - cute but not precise enough for my intentions. I am more interested in a lab type instrument. > > Basically what I am looking for is a curve tracer that has a micro attached to it that have some A/D's on them that can record the data of interest (e.g. Ib (vb), Vce, etc. > I've considered an arduino based approach but they have the limitations of 5V max on the input for the A/Ds and don't want to scale it. > I've looked for old Heathkit and Tek curve tracers that I could augment with a micro but they seem to be very scarce, in addition to having transistors in them that are NLA. > I could design one myself but in all honesty, I'd prefer to find something where someone has 'plowed the ground' and at the very most, I'd have to augment it with a micro. Yea, I am a bit lazy - the intent was to fix the amp, not develop a curve tracer.... > Thanks in advance > J >
My possibly-biased-by-youth opinion is that the transistor curve tracer is a mostly obsolete instrument from a time when transistors were expensive and manufacturing tolerances sucked balls and duff/under-performing parts were commonplace, that's not year of our Lord 2018, discrete transistors are cheap and quality is excellent. Like maybe if you needed to well-characterize RF or microwave amp transistors to get all the relevant information about their parameters that they often don't include on datasheets, for large-scale manufacture, maybe useful, an arduion/AVR based design will probably not be able to do that however. But just for audio circuits like why do this, the schematics/service manuals for just about everything ever sold are available online and I can't recall ever not being able to find an appropriate substitution cross-reference with a bit of searching
On 10/28/2018 09:26 PM, bitrex wrote:
> On 10/28/2018 08:46 PM, jjhudak4@gmail.com wrote: >> I find myself in a situation where I am repairing some high end audio >> amps and cassette decks that have house numbered semiconductors, >> mainly transistors as well as JDEC p/n that are NLA. >> >> I have found a few transistors that are dead and need to be replaced. >> Fortunately, they are in parts of the amp where the other channel has >> an identical transistor. >> Having one transistor as a base will allow me to match something close >> to the original. >> >> I have made (in the past)  the typical transistor curve tracer that >> shows the curves on a scope - cute but not precise enough for my >> intentions. I am more interested in a lab type instrument. >> >> Basically what I am looking for is a curve tracer that has a micro >> attached to it that have some A/D's on them that can record the data >> of interest (e.g. Ib (vb), Vce, etc. >> I've considered an arduino based approach but they have the >> limitations of  5V max on the input for the A/Ds and don't want to >> scale it. >> I've looked for old Heathkit and Tek curve tracers that I could >> augment with a micro but they seem to be very scarce, in addition to >> having transistors in them that are NLA. >> I could design one myself but in all honesty, I'd prefer to find >> something where someone has 'plowed the ground' and at the very most, >> I'd have to augment it with a micro.  Yea, I am a bit lazy - the >> intent was to fix the amp, not develop a curve tracer.... >> Thanks in advance >> J >> > > My possibly-biased-by-youth
"youth", in quotes I'm just shy of 40
>""youth", in quotes I'm just shy of 40 "
Wow, that explains why you're not conservative. You will be in about ten years, and don't worry, it doesn't hurt.
jjhu...@gmail.com wrote:
> > > I find myself in a situation where I am repairing some high end > audio amps and cassette decks that have house numbered semiconductors, > mainly transistors as well as JDEC p/n that are NLA. >
** It's " JEDEC " = Joint Electron Device Engineering Council. The full specs for JEDEC semis are always published and Google can search that for you. Also this page has a few more clues. https://www.elexp.com/Images/Reading_Transistor_Markings.pdf
> I have found a few transistors that are dead and need to be replaced. > Fortunately, they are in parts of the amp where the other channel has > an identic transistor. > Having one transistor as a base will allow me to match something close > to the original. > > I have made (in the past) the typical transistor curve tracer that shows > the curves on a scope - cute but not precise enough for my intentions. > I am more interested in a lab type instrument. >
** You are wasting your time, that is no way to even get close. I have a LOT of experience with substituting transistors found in all brands of hi-fi and pro audio electronics. There are plenty of clues to be found & used in choosing suitable replacements for obsolete and code numbered parts. Sometimes devices need to be Vbe and/or Hfe matched - circuit topology is the big clue there. Hint: watch out for TO3 devices that seem like ordinary power transistors but are in fact Darlingtons. ..... Phil
On Sun, 28 Oct 2018 18:33:48 -0700 (PDT), jurb6006@gmail.com wrote:

>>""youth", in quotes I'm just shy of 40 " > >Wow, that explains why you're not conservative. You will be in about ten years, and don't worry, it doesn't hurt.
Nope. Not smart enough to learn.
On 10/28/2018 09:33 PM, jurb6006@gmail.com wrote:
>> ""youth", in quotes I'm just shy of 40" > > Wow, that explains why you're not conservative. You will be in about ten years, and don't worry, it doesn't hurt. >
I'm probably too long-time New Englander for that I'm afraid, why in the world would I join a party so beloved by these whackjob "Real America" holy-roller evangelicals? scumbag scam-artists the lot of 'em and anyone who panders to them