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fewer through-hole transistors available
On 17/02/17 09:03, Dave Platt wrote:
I was repairing a piece of old equipment, and needed a replacement RF transistor. Checking at Digi-Key, I found very thin pickings, so i checked a few other distributors, and found the same situation. They seemed to have a modest choice of SMT transistors, but REALLY thin variety in T0-92 and similar plastic packages. Not a good sign, as we have a lot of 30 - 40 year old nuclear instrumentation here. Yup. The last five years or so have been dire times for through-hole semiconductors. A lot of the popular parts are now gone, past the end of the "lifetime buy" cycle from their original manufacturers. I've been trying to stock up my own (hobbyist-level) supplies of useful TO-92 transistors... Why? You're not doing production if 100 is lifetime. If it's for prototyping, why not just learn to prototype in SMT? It's not that hard. A lot of RF things are easier because stuff is physically smaller. |
fewer through-hole transistors available
I was repairing a piece of old equipment, and needed a replacement RF
transistor. Checking at Digi-Key, I found very thin pickings, so i checked a few other distributors, and found the same situation. They seemed to have a modest choice of SMT transistors, but REALLY thin variety in T0-92 and similar plastic packages. Not a good sign, as we have a lot of 30 - 40 year old nuclear instrumentation here. Another issue is the circuit is a differential NPN pair set up as a one- shot. So, it was running about 23 mA through one transistor at idle, and all of these on-at-idle transistors have failed. (The other transistors in the pairs seem fine.) The part actually in the unit is an FMT1190, which certainly seems like it should have been able to handle that current long- term. After replacing it with the best thing I could find, the transistor only has about 2V C-E, so the power dissipation is less than 50 mW, shouldn't have burned them out. I'm wondering if somehow the startup condition exceeded the base ratings. Anyway, I'll replace the transistors and burn it in for a while and see if it gives any more trouble. Jon |
fewer through-hole transistors available
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fewer through-hole transistors available
On Thursday, February 16, 2017 at 2:57:41 PM UTC-5, Jon Elson wrote:
I was repairing a piece of old equipment, and needed a replacement RF transistor. Checking at Digi-Key, I found very thin pickings, so i checked a few other distributors, and found the same situation. They seemed to have a modest choice of SMT transistors, but REALLY thin variety in T0-92 and similar plastic packages. N I have found that but-for a very few specialized transistors, most of the general purpose types are now lumped into a much smaller universe of replacement types. I have never had any problems, ultimately, with finding replacements - and I keep a variety of testers and checkers to make sure they will do - but they are not necessarily to OEM spec. Usually much better. Then, I am a hobbyist dealing in onesie-twosies. So I can afford to go up a couple of notches if necessary. Peter Wieck Melrose Park, PA |
fewer through-hole transistors available
Ralph Mowery wrote:
I worked in industry and had a lot of older instruments. Some were a real pain to work on and the factory did not support them any more. We, as the repair shop, told management they were just going to have to bite the bullet and update them. Well, this is modular signal processing modules, we have a wall of probably 400 of them of all different types. The companies that made this stuff in the 1970s are mostly out of the business, and most of the modules we have have no currently manufactured replacement. So, we don't have a lot of choice. Some modules have been so troublesome we have, indeed, retired them. Jon |
fewer through-hole transistors available
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fewer through-hole transistors available
Jon,
You have spoken of generic issues and some specs for a replacement. What was the original part number? Perhaps there are existing substitutions available. Dan |
fewer through-hole transistors available
I was repairing a piece of old equipment, and needed a replacement RF
transistor. Checking at Digi-Key, I found very thin pickings, so i checked a few other distributors, and found the same situation. They seemed to have a modest choice of SMT transistors, but REALLY thin variety in T0-92 and similar plastic packages. Not a good sign, as we have a lot of 30 - 40 year old nuclear instrumentation here. Yup. The last five years or so have been dire times for through-hole semiconductors. A lot of the popular parts are now gone, past the end of the "lifetime buy" cycle from their original manufacturers. I've been trying to stock up my own (hobbyist-level) supplies of useful TO-92 transistors - a mix of general-purpose jellybeans, RF amps, JFETs, and low-noise audio parts - whenever I can. I figure that a bag of 100 of any particular type constitutes a "lifetime buy" for me. For parts that have only recently gone obsolete, you might want to check with Rochester Electronics. They seem to have a pretty good stock of a lot of parts that Digi-Key and Mouser have dropped. There's a $100 line-order minimum, but it might be worth selecting a few useful parts and investing some $$ in a lifetime stock. Another issue is the circuit is a differential NPN pair set up as a one- shot. So, it was running about 23 mA through one transistor at idle, and all of these on-at-idle transistors have failed. (The other transistors in the pairs seem fine.) The part actually in the unit is an FMT1190, which certainly seems like it should have been able to handle that current long- term. After replacing it with the best thing I could find, the transistor only has about 2V C-E, so the power dissipation is less than 50 mW, shouldn't have burned them out. I'm wondering if somehow the startup condition exceeded the base ratings. Maybe a short inverse spike condition during powerup, which reverse-biases the base and makes it avalanche? Or, is there any chance that when the one-shot fires, the transitions are slow enough that the transistor passes outside of its SOA while turning on or off? |
fewer through-hole transistors available
In article om,
Clifford Heath wrote: I've been trying to stock up my own (hobbyist-level) supplies of useful TO-92 transistors... Why? You're not doing production if 100 is lifetime. If it's for prototyping, why not just learn to prototype in SMT? It's not that hard. A lot of RF things are easier because stuff is physically smaller. I do more prototyping in SMT these days when I'm puttering with a new design of any complexity... have even put together a toaster-oven- based setup with a ramp-and-soak controller. For repairing older audio equipment and RF test gear which was designed with through-hole parts, or for doing Manhattan-style prototypes, I still find it easier to stick with through-hole components. |
fewer through-hole transistors available
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fewer through-hole transistors available
Dave Platt wrote:
Maybe a short inverse spike condition during powerup, which reverse-biases the base and makes it avalanche? Analyzing the bias supply for the base, I can't really SEE how it could get a reverse voltage spike. I certainly thought about this on power-up. OHHH, wait! Maybe it could be on power DOWN! There is a bias network on the base with a capacitor to ground, and the supply to the emitters is connected to a reference supply that might dump VERY quickly when power is cut off. That could maybe put about -6 V bias on the base when the emitter supply drains back toward zero. I could probably stick a diode there to limit the reverse bias. Or, is there any chance that when the one-shot fires, the transitions are slow enough that the transistor passes outside of its SOA while turning on or off? Well, maybe. But, it is only 23 mA, and differential pairs are usually pretty benign when they transition. We just got this module out of a pile of stuff, it is the only one we have, and we have no history on it. It might have sat in some setup for 30 years powered on. Or, it might have experienced some kind of transient failure of the power supply that powered it in the past. This one-shot can't go over 100 ns, and the transition should be REALLY sharp, just a couple of ns. So, the only way to know if it will be reliable is to test it a bit. Thanks, Jon |
fewer through-hole transistors available
An A430 crosses to an NTE 161 which is a UHF-VHF amp. Since the FMT1190 is an RF-IF AMP, this should work as well. I know that these are available (NTE160).
While I am not a fan of NTE devices, they will work in a pinch. Give this a try. If you can't find one, let me know. I have some in stock. Dan |
fewer through-hole transistors available
In article ,
Jon Elson wrote: Analyzing the bias supply for the base, I can't really SEE how it could get a reverse voltage spike. I certainly thought about this on power-up. OHHH, wait! Maybe it could be on power DOWN! There is a bias network on the base with a capacitor to ground, and the supply to the emitters is connected to a reference supply that might dump VERY quickly when power is cut off. That could maybe put about -6 V bias on the base when the emitter supply drains back toward zero. I could probably stick a diode there to limit the reverse bias. Probably a good idea, and (assuming that the diode's capacitance when biased-off isn't a problem) it should be good cheap protection. Thinking about it... I wonder whether those poor old transistors might not just have been Plumb Tuckered Out? A friend of mine has told stories about the early generations of Fairchild transistors - the mushroom-shaped ones with a plastic case - and said that a lot of them he'd dealt with had failed over the years as a result of problems with the encapsulations. Apparently the plastic didn't seal to the leads very well, allowed oxygen to infiltrate, and the internal wire-bonds or metallization would oxidize and fail over time. Possibly this is something which might have affected those old parts of yours, with the (modest) amount of heat in the "on at idle" transistors having the effect of accelerating the aging process. |
fewer through-hole transistors available
On 02/16/2017 02:57 PM, Jon Elson wrote:
I was repairing a piece of old equipment, and needed a replacement RF transistor. Checking at Digi-Key, I found very thin pickings, so i checked a few other distributors, and found the same situation. They seemed to have a modest choice of SMT transistors, but REALLY thin variety in T0-92 and similar plastic packages. Not a good sign, as we have a lot of 30 - 40 year old nuclear instrumentation here. Another issue is the circuit is a differential NPN pair set up as a one- shot. So, it was running about 23 mA through one transistor at idle, and all of these on-at-idle transistors have failed. (The other transistors in the pairs seem fine.) The part actually in the unit is an FMT1190, which certainly seems like it should have been able to handle that current long- term. After replacing it with the best thing I could find, the transistor only has about 2V C-E, so the power dissipation is less than 50 mW, shouldn't have burned them out. I'm wondering if somehow the startup condition exceeded the base ratings. Anyway, I'll replace the transistors and burn it in for a while and see if it gives any more trouble. Jon A whole lot of TO92s went away in the last couple of years. I bought several thousand as a lifetime prototyping supply. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
fewer through-hole transistors available
On 02/16/2017 12:46 PM, Clifford Heath wrote:
On 17/02/17 09:03, Dave Platt wrote: I was repairing a piece of old equipment, and needed a replacement RF transistor. Checking at Digi-Key, I found very thin pickings, so i checked a few other distributors, and found the same situation. They seemed to have a modest choice of SMT transistors, but REALLY thin variety in T0-92 and similar plastic packages. Not a good sign, as we have a lot of 30 - 40 year old nuclear instrumentation here. Yup. The last five years or so have been dire times for through-hole semiconductors. A lot of the popular parts are now gone, past the end of the "lifetime buy" cycle from their original manufacturers. I've been trying to stock up my own (hobbyist-level) supplies of useful TO-92 transistors... Why? You're not doing production if 100 is lifetime. If it's for prototyping, why not just learn to prototype in SMT? It's not that hard. A lot of RF things are easier because stuff is physically smaller. SMT prototyping is about a factor of 10 slower than dead bug using through-hole parts. Every DIP package gets you a bunch of nice strong standoffs. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
fewer through-hole transistors available
Dave Platt wrote:
Thinking about it... I wonder whether those poor old transistors might not just have been Plumb Tuckered Out? Yes, that is another possibility I considered. If the module had been in use for a long time, with no cooling, these are the highest power dissipation of all the signal transistors in the unit. Always on at 23 mA. I repaired an HP synthesizer that had about 400 Germanium transistors in it, and about a dozen had failed. I replaced them with Silicon transistors and then sold it on eBay before any more units went out. Jon |
fewer through-hole transistors available
On 02/17/2017 02:31 PM, Michael Black wrote:
On Fri, 17 Feb 2017, Jon Elson wrote: Dave Platt wrote: Thinking about it... I wonder whether those poor old transistors might not just have been Plumb Tuckered Out? Yes, that is another possibility I considered. If the module had been in use for a long time, with no cooling, these are the highest power dissipation of all the signal transistors in the unit. Always on at 23 mA. I repaired an HP synthesizer that had about 400 Germanium transistors in it, and about a dozen had failed. I replaced them with Silicon transistors and then sold it on eBay before any more units went out. I thought germanium transistors in general had a tendency to go bad over time. They'd start leaking. Maybe manufacturing improved over time, but then at some point, silicon took over completely, except for a handful of uses. So you can't easily get replacements, because few germanium devices are made now. Michael Point contact devices especially. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
fewer through-hole transistors available
On Fri, 17 Feb 2017, Jon Elson wrote:
Dave Platt wrote: Thinking about it... I wonder whether those poor old transistors might not just have been Plumb Tuckered Out? Yes, that is another possibility I considered. If the module had been in use for a long time, with no cooling, these are the highest power dissipation of all the signal transistors in the unit. Always on at 23 mA. I repaired an HP synthesizer that had about 400 Germanium transistors in it, and about a dozen had failed. I replaced them with Silicon transistors and then sold it on eBay before any more units went out. I thought germanium transistors in general had a tendency to go bad over time. They'd start leaking. Maybe manufacturing improved over time, but then at some point, silicon took over completely, except for a handful of uses. So you can't easily get replacements, because few germanium devices are made now. Michael |
fewer through-hole transistors available
"Jon Elson" wrote in message ... wrote: I have found that but-for a very few specialized transistors, most of the general purpose types are now lumped into a much smaller universe of replacement types. I have never had any problems, ultimately, with finding replacements - and I keep a variety of testers and checkers to make sure they will do - but they are not necessarily to OEM spec. Usually much better. This particular one was an NPN with an ft of 1400 MHz and 1.2 pF Cob. So, definitely, a 2N2222 would not cut it. Once a neigbour broke the TO92 RF transistor in their wireless doorbell button. Nothing anywhere near in my junk box, so I salvaged the SMD RF transistor from a scrap mobile phone and put it on "stilts". It worked well enough, but it turns out a few other people along the street had the same doorbell on the same code setting................ |
fewer through-hole transistors available
"Jon Elson" wrote in message ... wrote: Jon, You have spoken of generic issues and some specs for a replacement. What was the original part number? Perhaps there are existing substitutions available. Dan The part on the board was a Fairchild FMT1190. The part on the schematic was an A430, which I can't even find a datasheet for. Was it PNP - could start with 2SA.... |
fewer through-hole transistors available
"Phil Hobbs" wrote in message ... On 02/16/2017 12:46 PM, Clifford Heath wrote: On 17/02/17 09:03, Dave Platt wrote: I was repairing a piece of old equipment, and needed a replacement RF transistor. Checking at Digi-Key, I found very thin pickings, so i checked a few other distributors, and found the same situation. They seemed to have a modest choice of SMT transistors, but REALLY thin variety in T0-92 and similar plastic packages. Not a good sign, as we have a lot of 30 - 40 year old nuclear instrumentation here. Yup. The last five years or so have been dire times for through-hole semiconductors. A lot of the popular parts are now gone, past the end of the "lifetime buy" cycle from their original manufacturers. I've been trying to stock up my own (hobbyist-level) supplies of useful TO-92 transistors... Why? You're not doing production if 100 is lifetime. If it's for prototyping, why not just learn to prototype in SMT? It's not that hard. A lot of RF things are easier because stuff is physically smaller. SMT prototyping is about a factor of 10 slower than dead bug using through-hole parts. Every DIP package gets you a bunch of nice strong standoffs. I regularly include SMD parts in dead-bug prototypes. With a bit of thought and planning they can reduce wire links instead of increasing them, they also tend toward adding rigidity to the assembly. |
fewer through-hole transistors available
"Michael Black" wrote in message news:alpine.LNX.2.02.1702171429360.15904@darkstar. example.org... On Fri, 17 Feb 2017, Jon Elson wrote: Dave Platt wrote: Thinking about it... I wonder whether those poor old transistors might not just have been Plumb Tuckered Out? Yes, that is another possibility I considered. If the module had been in use for a long time, with no cooling, these are the highest power dissipation of all the signal transistors in the unit. Always on at 23 mA. I repaired an HP synthesizer that had about 400 Germanium transistors in it, and about a dozen had failed. I replaced them with Silicon transistors and then sold it on eBay before any more units went out. I thought germanium transistors in general had a tendency to go bad over time. They'd start leaking. Maybe manufacturing improved over time, but then at some point, silicon took over completely, except for a handful of uses. So you can't easily get replacements, because few germanium devices are made now. In the very early days, germanium transistors were epoxy potted - it wasn't very moisture proof. They've been much better since hermetically sealed metal cans. If you're used to silicon, the leakage on germanium devices is going to seem pretty dire anyway. |
fewer through-hole transistors available
"Phil Hobbs" wrote in message ... On 02/16/2017 02:57 PM, Jon Elson wrote: I was repairing a piece of old equipment, and needed a replacement RF transistor. Checking at Digi-Key, I found very thin pickings, so i checked a few other distributors, and found the same situation. They seemed to have a modest choice of SMT transistors, but REALLY thin variety in T0-92 and similar plastic packages. Not a good sign, as we have a lot of 30 - 40 year old nuclear instrumentation here. Another issue is the circuit is a differential NPN pair set up as a one- shot. So, it was running about 23 mA through one transistor at idle, and all of these on-at-idle transistors have failed. (The other transistors in the pairs seem fine.) The part actually in the unit is an FMT1190, which certainly seems like it should have been able to handle that current long- term. After replacing it with the best thing I could find, the transistor only has about 2V C-E, so the power dissipation is less than 50 mW, shouldn't have burned them out. I'm wondering if somehow the startup condition exceeded the base ratings. Anyway, I'll replace the transistors and burn it in for a while and see if it gives any more trouble. Jon A whole lot of TO92s went away in the last couple of years. I bought several thousand as a lifetime prototyping supply. What I've harvested from scrap gear should last some time yet. |
fewer through-hole transistors available
On 02/17/2017 03:55 PM, Benderthe.evilrobot wrote:
"Phil Hobbs" wrote in message ... On 02/16/2017 12:46 PM, Clifford Heath wrote: On 17/02/17 09:03, Dave Platt wrote: I was repairing a piece of old equipment, and needed a replacement RF transistor. Checking at Digi-Key, I found very thin pickings, so i checked a few other distributors, and found the same situation. They seemed to have a modest choice of SMT transistors, but REALLY thin variety in T0-92 and similar plastic packages. Not a good sign, as we have a lot of 30 - 40 year old nuclear instrumentation here. Yup. The last five years or so have been dire times for through-hole semiconductors. A lot of the popular parts are now gone, past the end of the "lifetime buy" cycle from their original manufacturers. I've been trying to stock up my own (hobbyist-level) supplies of useful TO-92 transistors... Why? You're not doing production if 100 is lifetime. If it's for prototyping, why not just learn to prototype in SMT? It's not that hard. A lot of RF things are easier because stuff is physically smaller. SMT prototyping is about a factor of 10 slower than dead bug using through-hole parts. Every DIP package gets you a bunch of nice strong standoffs. I regularly include SMD parts in dead-bug prototypes. With a bit of thought and planning they can reduce wire links instead of increasing them, they also tend toward adding rigidity to the assembly. Sure, me too. I disagree about rigidity though. RN60C resistors are pretty rigid. ;) I've recently done a mid-air proto using 0402s--like five in a row in mid air--but that was a 100-ps sampler, so it was worth the trouble. Ordinary dead bug is good to 1 GHz or so, and it's a lot easier. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.neth |
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