Thanks Hugh for the story, and thanks for the schematic! Quite interesting. There is a little strangeness: the wave clipper darlington transistor Q1 is marked as 1854-0611, equivalent to the standard darlington 2N6055. But why there is a simple 2N3055 in the picture? Some sort of version update fail? Thanks Cheers Luca iw2lje
Il giorno sabato 9 febbraio 2019, Rice, Hugh (IPH Writing Systems) < [email protected]> ha scritto: > I grew up on Silicon Valley (Santa Clara Valley, California), graduating > from High School in 1980. My home town is Cupertino, also the home of > Apple Computer. During my formative teen years in the 1970s, HP was THE > company in the valley, the elder statesmen of Hi-Tech. (Apple was just a > small upstart business for computer geeks, and their headquarters were just > down Bubb Road from my HS.) The reputation of HP as a great company was > untouchable. Both in the quality of the products, and as a the best place > to work. Being from Silicon Valley, I choose to study electrical > engineering (rather than my natural inclination towards mechanical > engineering, having done a lot of work on cars and bicycles), hoping to > come back to the area to work when I graduated. I had fantasies of > working for HP in my college summers as a “SEED” student, but was never > able to make the right connections. A HP job upon graduation with a BSEE > was like winning the lottery, especially for a Silicon Valley Kid. > > Home for Christmas during my senior year, I was visiting a friend from > church, and her dad (Charles Adams) asked me how my job search was going, > and if I had considered working for HP. “I’d LOVE to work for HP. I just > can’t crack in and get an interview.” He said they had an opening for a > new grad EE, and asked if I would be interested in considering it. “Uh, > yes!” A few days later, I was in the Precision Frequency Sources > Production Engineering area, doing the all day rounds of a classic HP > interview. I did well enough that they offered me a job the next day, and > I went back to school for my final semester with a HP job in hand. A > certifiable miracle. It didn’t get any better than this. > > I asked Charles what I could do to prepare for the job, and he mailed me a > 5061A Operating and Service Manual to review. It was incomprehensible. > But I could tell that the 5061A was something pretty special, because all > the circuit diagrams and theory of operation descriptions had things in > them that even the grad students I knew couldn’t understand. And I had a > job at HP! Working on Atomic Clocks! (Whatever they were.) > > As you know from past postings, my job was part of the 5061A to 5061B > development team. The first task I was assigned to was to freshen up A2 > Battery Charger Assembly. The purpose of this circuit was to keep the 20 > cell NiCad backup battery ready to supply power in emergencies. The must > fix issue was a gigantic mica capacitor used in a RC timing circuit, which > was both expensive and unprocurable. I think my mentor, Roberto, > encouraged me to look over the whole circuit, and sift out all the other > old parts that would a problem in the near future. (All that code 4 part > stuff.) > > So I studied the circuit like only a new grad can do. Brand new > engineers are nearly worthless, and no one has any reason to talk to them > or distract them. This was before the internet, cell phones, email (at my > location), and any other distraction. I had hours and hours of > uninterrupted time. The circuit was strikingly complex for a battery > charger. But you have to remember by frame of reference. HP was the > best electrical engineering company in the world. Their products were > awesome. Surely every circuit in every product was the result of deep > expertise from brilliant engineers, and every resistor, capacitor and > transistor had a sacred purpose. So I kept digging until I understood > every aspect of the circuit. > > The “brilliant” designer had decided that the battery charger needed to be > a two-level system. A fast charge to replenish the battery quickly after > a power failure, and then a lower “trickle” charge to keep it topped off > long term. But how long to do the fast charge? Well, if we time the > discharge time, we can then use that to set the fast charge time. Battery > power for 20 minutes? Fast charge 20 minutes at a similar rate. In > addition, the charger assembly had a drop-out relay circuit, so if the > battery voltage got too low, the relay would trip to disconnect the battery > protect it from over discharge. (Oh yes, the relay used was also > impossible to procure, being some ridiculous double pole, double throw, > part unique to the 5061A). Add another circuit to flash the front panel > light when the back-up battery was supplying power. And then the charge > current regulator itself, which of course was a transistor level fully > discrete design with dozens of components. > > But it gets better: The discharge, recharge timing circuit used the most > complex counter IC available from the TI TTL catalog. A pre-settable, > programable, up-down counter. There may have been two counters, for 8 > bits of resolution. To make it better, the counters were pre-set to a > specific but obscure number, that had them exactly count down to zero > after about 90 minutes, when using the timing rate set by the RC circuit > with the aforementioned giant unprocurable Mica capacitor. > > I wish I could find a circuit diagram of the 5061A, to fully relive the > experience and share it with you all. > > OK, now that I finally had the circuit figured out, what do I do? I > think Roberto recommended that I read the “GE Battery Book”, since GE was > the supplier of the Ni-CAD battery pack, to give me background on > rechargeable batteries. I bought a new copy, and read the whole thing > cover to cover in a couple of days. All kinds of information on charging > at the “C” rate (a 1Amp Hour battery “C” factor is 1 Amp) for fast > charging, and 0.1C for trickle charging (full charge in 10 hours), and how > trickle charging is best for the batteries, and so forth. > > As I’m reading the GE book, I’m slowing realizing that the 5061A battery > charger is pretty complicated, for what appears to be a fairly simple > task. As I chat with Roberto more about it, it becomes clear that the > circuit is perhaps a bit over complicated. But wait, aren’t HP engineers > the best in the world, and every circuit they design the best possible > implementation known to man? The idolization I had developed from my > Silicon Valley roots, and all the praise from my university professors and > peers is starting to loose its luster. This battery charger wasn’t a > great design. I wasn’t even a good design. It was a ridiculously > complicated, expensive, idiotic design that never should have made it > through any sensible design review. I never did learn who did the work. > I don’t think they worked at Santa Clara Division any more. Probably a > good thing. > > This was actually a blessing in disguise. Only a few months into my HP > career I learned the priceless lesson that inherited work isn’t always good > work. I also learned to really understand the task that needed to be done, > before you set out to do it. Like learn how batteries work before > designing chargers. And then I had the opportunity to design a completely > new circuit from scratch. > > I had a new goal: Make a good, simple, reliable battery charger, but it > had to be backwards compatible to the 5061A. HP didn’t want to support > the old design any more (huge mica capacitors and crazy relays), and the > new circuit needed to be a replacement assembly too. This presented > another priceless lesson: real work design is often constrained, and not > clean sheet like those university projects. > > I’m still proud of the final battery charger design. So proud that > attached the 5061B circuit diagram if you want to be impressed. 😊 I > ditched the timing circuits altogether, and just went a simple trickle > charger. If a 5061B application has a power outage of 30+ minutes, how > likely are they going to have another long power outage within the next few > hours? Not very. The new circuit used standard, inexpensive, robust > components in the whole design. There are other clever (to me) aspects, > and you can discover them on your own if you are interested. > > One last story on this. My first prototype of the circuit was hand > soldered together on proto-board material. That generic PCB with grids of > 0.10” pitch holes all over it. Roberto told me to go to the 5061A > production line tech’s, and have them try out the new circuit. Picture a > brand new engineer who looks about 17 years old, with this rats nest of a > proto circuit for them to test. I recall one of the Tech’s, Ray, putting > on safety glasses before he put it in a test 5061A and powered it up. They > never wore safety glasses. I don’t think it worked on the first try. > But I recall that the problem was something simple to resolve. > > Over the next few years, HPs iconic reputation would continue to loose > it’s luster in my eyes, as I learned that mortal people worked there, and > that real business had real problems. But there were also a lot of > really good engineers and technicians there, and they would help you if you > asked. > > It was a fantastic start to a 35 year (and counting) career at HP. > > Happy Chinese New Year from Singapore, > > Hugh Rice > > > > > > > > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
