# Modern Circuit Diagrams



## jaydeeare (Feb 5, 2008)

For the less young amongst us, how do you feel regarding the modern electronic circuit diagrams?

Having been brought up on valves in the 60's, to me they are just a lot of squares and rectangles with lines coming in and out of them, and make very little sense.

At least with the old diagrams with valves and transistors, they were a lot easier to read, and could understand what was happening.

Some years ago, I went for a job interview and a huge circuit was pushed in front of me. Pointing to a device, I was asked what such and such was doing. I asked for a Data Book, and was told, "What for? it's used here....here...here...etc." I told him I hadn't heard of that device before. I was then shown another 'square' and asked what that was doing. Same thing. I'm still waiting to hear if I got the job or not, and that was 27 years ago!


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## BobClay (Dec 14, 2007)

Have to admit the one on the right is more interesting than the one on the left ....

(Thumb)


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## Harrisman (Jul 13, 2006)

I have sailed with the so called 'electronic experts' and when anything went wrong they went into the cabinets and wanted to pull cards and try to be smart when in fact 99.9% of faults were not on anything electronic but on things like proximity switches, limit switches, electro pneumatic convertors etc. due to them being out in such a hot, humid and unfriendly environment.
I did a two week course course in Siemens in Germany and our lecturer who was brilliant said you really do not need to be an electronic 'expert' so long as you know what signal is going in and what should be coming out and if its not right change the card but that happens so rarely as the fault will be out with the nice air conditioned control room ... air conditioned for the electronic instrumentation and certainly not for the engineers as has been mentioned in many threads


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## benjidog (Oct 27, 2005)

"Black Box" design. Nobody is needs to to know what goes on inside apart from the designers. 

As Harrisman says - something goes in one end and comes out transformed in some way. Basically "magic happens" inside - and if it stops working you chuck the component away and put a new one in. Of course if the magic still doesn't happen you are no further forward. So you replace the whole thing of which this is a part and so on.

Same thing with cars, same thing with central heating boilers, same thing with computers. 

Maintenance these days amounts to "God knows what it does but the electronic diagnostics say it is buggered so replace it."


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## trotterdotpom (Apr 29, 2005)

Not everything has been miniaturised. I remember multi-vibrator circuits being contained in a area of a square inch. Nowadays I see single vibrators 10 inches long - what's gone wrong there?

John T.


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## Bill Greig (Jul 4, 2006)

Miniaturised! Tell me about it, in here we use mostly surface mount components. 0805 package is small, 0603 is half that size and 0402 is even smaller, I can't see the little b***ers now, sneeze at the wrong time and half the components disappear! Where's my glasses.


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## mikeg (Aug 24, 2006)

trotterdotpom said:


> Not everything has been miniaturised. I remember multi-vibrator circuits being contained in a area of a square inch. Nowadays I see single vibrators 10 inches long - what's gone wrong there?
> 
> John T.


Thats because its a relaxation oscillator (Jester)


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## K urgess (Aug 14, 2006)

Even when computer engineering in the "good old days..." it was always a matter of checking if the steam was going in and if so was the right sort coming out of a board.
In order to be super efficient, the board (foolscap paper size or larger), was swapped out so that the customer was producing the correct steam as quickly as possible.
Unfortunately the replaced board then had to be fixed at component level. Fortunately the chips were mostly 74 series with the odd specialist big black multi-leg thrown in. It was pretty simple even for a dinosaur trained on valve gear in the mists of time.
Just get used to boards made up of lots of little black boxes and then get presented with a big black box that did the same job.
Dinosaur time again. (Sad)
Look at your current gigabytes of memory and compare with the attached.
First one too big for an A4 scanner bed and a whole 4,000 bytes of memory.
We didn't get oscilloscopes we got microscopes. [=P]
Second one shows how battered it's got from 30 years of knocking around various houses.
My second childhood is full of valve gear and clocks.(==D)


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## Shipbuilder (Jun 30, 2005)

I keep my brain honed to a razors edge between building model ships with building vintage-style radios. Here is a recent one using two EF91s. The strange looking device on the left with a brass brush on top is my own version of reaction where an RF choke is physically rotated against the lower end of the aerial coil. The aerial and reaction coils are a combination of 100uH & 47uH miniature RF chokes inside empty 1 1/4 inch glass cartidge fuses.
It often takes quite a lot of effort to get them to work as not only has the circuit to be correct, but the layout and wiring has to be made in such a way that nothing interacts incorrectly with anything else. A single wire misplaced can stop the whole thing working!

Quite pointless of course, but gives me endless hours of enjoyment!

Bob


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## jaydeeare (Feb 5, 2008)

Ahhhhh!! Real electronics!

Thanks for your insights and recollections 

Valves always taught one big lesson - being careful!


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## BobClay (Dec 14, 2007)

You can always tell valve men, they tremble a lot. 

You just don't get that with 5 volts.

(Jester)


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## jaydeeare (Feb 5, 2008)

BobClay said:


> You can always tell valve men, they tremble a lot.
> 
> You just don't get that with 5 volts.
> 
> (Jester)


They also roll their sleeves up and remove watches, rings etc. before going anywhere near anything electronic or electric!


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## K urgess (Aug 14, 2006)

jaydeeare said:


> They also roll their sleeves up and remove watches, rings etc. before going anywhere near anything electronic or electric!


Only after some salutory lessons and practical demonstrations of the conductivity of the human body. [=P]


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## surfaceblow (Jan 16, 2008)

Don't forget about grounding themselves before playing with the chips. 

I also had a early light sensitive chip that was programed to average the gas pressure for a LNG Plant burner management system. The curious peeled the tape off the chip and looked inside the chip with his flash light. 

The replacement chip did not have the same program as the original. There was no time delay and after resetting the counter to zero there was a error message since you could not divide by zero. Every 13 hours or so the gas plant would trip. Requiring to restart the gas compressor and relighting the gas burners.


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## jaydeeare (Feb 5, 2008)

Marconi Sahib said:


> Only after some salutory lessons and practical demonstrations of the conductivity of the human body. [=P]


Nice way to describe a belt!


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## andysk (Jun 16, 2005)

benjidog said:


> "Black Box" design. Nobody is needs to to know what goes on inside ....... Basically "magic happens" inside .......


I once worked for a guy who used to have a box in every system block diagram marked with the letters "SMH".

These diagrams were shown around, sent around, projected and explained to all and sundry, from apprentices to big cheeses, and only one person in about 5 years ever asked what the letters stood for !


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## Vital Sparks (Sep 19, 2007)

I once came across a radar fitted with a "bucket and thimble" integrator consisting of a relay which was being pulsed so that it's contacts were switching a very small capacitor to dump it's charge into a very large capacitor. To avoid surface current leakage this circuit had to be in a very dry environment and so was inside a hermetically sealed box but the major failure mode was found to be moisture ingress. This was caused by curious people taking the lid off and the solution was to fit a transparent lid.


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## Naytikos (Oct 20, 2008)

I agree that these days it is nigh-on impossible to tell what a circuit does simply by looking at the circuit diagram; even if the ICs are labelled, one cannot carry a comprehensive list of IC functions by type number in the head. Another problem is that, because components are now very cheap, designers tend to incorporate more of them.
In the early days of inert gas systems, on one ship I was asked to 'make it work' when a failure lamp illuminated and none of the fans or motors would start. Behind the control panel I found three PCBs with around half a dozen ICs on each, lots of wires connected to them and absolutely no labels at all. The ICs had been coated with paint and so could not be identified! Needless to say there was no manual.
With a 6-week passage PG- Europoort ahead I took the boards and very very carefully removed the paint with paint-stripper, stopping when the numbers became visible. I then 'reverse-engineered' them, tracing out the circuit of each board. At Capetown I had the relevant spares sent out with the stores and effected repair.
From Rotterdam I sent a fair copy of the final circuit diagram to the manufacturers of the IG system with a letter explaining the fault. Never did get a reply, though!


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## BobClay (Dec 14, 2007)

> From Rotterdam I sent a fair copy of the final circuit diagram to the manufacturers of the IG system with a letter explaining the fault.


I like the idea of someone out in the field sending in their own diagram to the manufacturer, with no doubt a small note saying 'By the way, this is how it works.'

Nice one.

(Thumb)


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## jaydeeare (Feb 5, 2008)

Naytikos said:


> I then 'reverse-engineered' them, tracing out the circuit of each board.
> From Rotterdam I sent a fair copy of the final circuit diagram to the manufacturers of the IG system with a letter explaining the fault. Never did get a reply, though!


You were fortunate it wasn't a multi-layer board with vias under the chips!


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## Naytikos (Oct 20, 2008)

Multi-layered boards hadn't been invented then!


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## CrazySparks (Apr 21, 2008)

Fascinating thread.
I was trained on both valves and chips in the mid 70's (Apollo receivers, etc) and valve auto-alarms with Eccles-Jordan flip-flops, as well as radars with discrete components astables!
In 84 I returned to studies and was astounded to see these damn' circuit diagrams with hairy boxes and tiny labels!.Trouble is, try drawing a really complex digital circuit line by line- the thing'd be useless.! Anyway, the problem was mainly solved by drawing data and address buses and abandoning individual connecting lines.

I went backwards on my first trip - had a electro-mechanical auto-alarm - maybe the older sparkies hated valves and preferred cogs?!!! Heh Heh!!!


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## jaydeeare (Feb 5, 2008)

At one of my first interviews coming out of the RAF, I was asked what sort of equipment I was working on. I told him it was 90% valve based. Once he picked himself off the floor.... well needless to say, I didn't get the job.

Yep! That last radar I worked on put out power in MW and the was water and air cooled with a 75 ton head!

Definately no discreet components in that lot!


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## Jeffers (Jan 4, 2006)

I remember that when I came ashore from the MN I did a government training course in "Radio & Television Servicing". It was 10 months full time and I enjoyed it immensely. Part of the course was to build a radio receiver (valve operated!) from scratch. I took great pride in laying all my wiring out in nice straight lines so that the interior "works" looked nice and tidy. Of course it didn't work very well, getting into all sorts of feedback loops as my bits of wire all picked up each others signals! Got it working eventually but it didn't look as pretty.
Built one or two things with ICs and transistors in later times but never quite got the same buzz as seeing the valves light up and sound starting to come from the speaker of that old radio.


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## David Williams (Sep 27, 2008)

*Job Interviews*

Hi Johnny.
I dont think that I would have had that job.
Todays jargon is way over my head.I was 
lost in the days of valves and fuse wire??

Dave Williams(R583900)


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## jaydeeare (Feb 5, 2008)

daishop1 said:


> Hi Johnny.
> I dont think that I would have had that job.
> Todays jargon is way over my head.I was
> lost in the days of valves and fuse wire??
> ...


My 'real' electronics days are over - thankfully. I don't need to delve into circuitry anymore. My usual way of fault finding with discrete components was to make notes of waveforms, levels and voltages when I found a board that worked, then used this as a comparison, plus a bit of 'logical guesswork'!

Fixed a lot of faults that way, but making notes on failure modes and the fix did for most of the rest.

Someone once told me if a fuse blows, stick in a bigger fuse. If that blows, use a bigger one and so on until something begins to glow, then replace that component. BY the time it comes back from repair, you'll probably be on another job, then it's someone elses problem! Never did follow that 'advice'.


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## BobClay (Dec 14, 2007)

> Someone once told me if a fuse blows, stick in a bigger fuse. If that blows, use a bigger one


A six inch nail is usually good ... :sweat: .... that is until the thermo-nuclear explosion.


[=P]


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## Naytikos (Oct 20, 2008)

I heard of that technique whilst at college and tried it out a few times. The most spectacular was on an Argonaut VHF, newly installed on a Bank boat shortly after I joined. It worked right after installation in Hamburg but then wasn't used until arriving at the Hook pilot station when the skipper thought we should try out the new-fangled communication device. It blew a fuse as soon as the PTT button was pressed. After 3 fuses I opened the cabinet and checked voltages. All were OK and, lo and behold, the fuse didn't blow and it worked. Put the cover back on and the next time it was used the fuse blew again. I got the message and put in a small nail, (6-inch wouldn't fit!). Pushed the PTT and heard a bang from the radio-room the other side of the bulkhead. 
For those unfamiliar with the Argonaut, it has three PCBs with lots of valves in B7G and B9A holders mounted thereon, in a shallow cabinet about 3 feet high, mounted on the bulkhead. The cover comes off the front leaving a back-plate with the PCBs and a PSU at the bottom. A row of terminals on a rail provide the power distribution. One of the joints on this had an excess of solder in a spike which had been touching the inside of the cover - immediately obvious because of the new large burn-mark.
That was easy to fix, however this was when I learnt to repair PCB tracks as several inches were now missing from the back of one of them!


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## Ron Stringer (Mar 15, 2005)

*Argonaut VHF*

You may recall that the Argonaut had a transceiver unit (containing the power supply unit as you describe) connected to one or more control units by means of multi-core cables - and I mean multi, each containing 25 or more cores. These core were distinguished by colour, having base colours and one or more coloured stripes. If there was to be more than one control unit, a switching box was first connected by multicores to the transceiver and then the required quantity of control units (maximum 3) were connected to the switching box, of course using further multicores. The cables were hard-wired into the control units during manufacture, with 'tails' at the free end to be connected to the transceiver or switching box, as required.

I was asked to go to a new fitting to help the installation engineer who was having problems making the Argonaut VHF work prior to the ship going on trials. When I arrived in the wheelhouse, my colleague was at the end of his tether because the set was doing the oddest things. I listened carefully to his list of symptoms and description of what he had done and the results that he had observed.

With sailing time only a couple of hours away we set-to to find the fault. Switching between control units to try and find some common factor was not productive, in fact that was even more confusing. So, following my usual habits I decided to start with the basics and measure the outputs of the power supply. I got out the handbook and identified the terminals and checked all the voltages. No problems there. However I did notice that one of the positive outputs had a black wire connected to it. That didn't seem right so I asked the other guy for the installation wiring diagram so that I could check that connection.

He looked at me in a puzzled way and asked if I meant the drawings that had been sent down for the ship's do***ent folder. I wasn't so sure about that and said, ''I don't know, show them to me.'' He got the folder out of a drawer in the radio room and shook the drawings out onto the deck. Having found the IWD, I unfolded it and started checking the connections on the transceiver terminal strip. Not one of them matched the drawing. So I opened up all the control units and the switching box, to find the same situation.

By now throughly confused I asked my colleague how he had arranged the wiring and why was it different from the drawing. He said that this was the first time he had installed an Argonaut and didn't appreciate that the cores had to be connected in any special way. He hadn't used the drawing but had just taken the first core to hand and connected it to terminal 1, another core to terminal 2, and so on until all cores had been used.

Panic stations, we set to disconnecting all the units and reconnecting them in accordance with the drawing. We tore the drawing into two pieces so that we could each have a list of the connections and, working as fast a possible completed the job as she let go and started down the Tyne. We switched on and nothing went bang. So we called the Tyne pilots and got an immediate response. Another call to Cullercoats and all was well. Having checked from all the control units, we were done and got off in the pilot boat beyond the Tyne piers.

Can't think that the solid state replacement for the Argonaut would have been quite so forgiving about being wired up randomly. (Never had to put it to the test).


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## K urgess (Aug 14, 2006)

You've probably got more computing power in your mobile phone than there is in the first picture attached. 
The print may be unreadable so the CPU was operating at a whole 900,000 cps (almost 1MHz). Storage on magnetic media like tapes or rack mounted disks (they say 80 or 160Mb but the ones I saw were only 11 or 23Mb with a removeable platter for storage) and the external storage module could cope with a whole 300Mb. Don't be fooled by the lovely green monitors which are displaying a VDU character test and a game called Hanoi. All using character graphics rather than pixel graphics.
At the bottom is a memory board with a staggering maximum of 256K of memory. Since they were 19" racks the board is 10" wide by 15" long. (EEK)
The point being that these were quite easy to work on and fault find. No multi-layer boards in those days and tracks you could solder.
Somewhere I have a picture of one of these set up in my front room. All £10,000's worth.
Just shows they thought a lot of themselves when the front of the advertising brochure has the headline "The last time it was penicillin".
The next attached is what came along in about 1982. Originally a Heathkit unit (TRS-80?) that came in about 1978 these final ones had gained Digico PCBs and 8Mb Winchester drives. Built around Z80 CPUs and peripherals with a standard backplane, that had no components other than terminating resistors, and slots for 6 boards. CPU, VDU, floppy controller, RAM, PROM, Serial/Parallel, Buffer boards in combination depending on application.
The drawings (all ammonia blueprints) were mind boggling and the next attachment shows the easy bit in one quarter. The last one is the next quarter and why most of the boards went back to the factory for repair. To keep us on the road rather than in the workshop we weren't expected to repair unless we had some spare time or the fault was simple. It ended up with the workshop sending me boards for repair when they got more complicated and closer to today's PCs.
I've still got these drawings because I still have one of these beasts in the loft that actually works (if I kick it in the right place). (Sad)


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## mikeg (Aug 24, 2006)

Marconi Sahib said:


> You've probably got more computing power in your mobile phone than there is in the first picture attached.
> The print may be unreadable so the CPU was operating at a whole 900,000 cps (almost 1MHz). Storage on magnetic media like tapes or rack mounted disks (they say 80 or 160Mb but the ones I saw were only 11 or 23Mb with a removeable platter for storage) and the external storage module could cope with a whole 300Mb. Don't be fooled by the lovely green monitors which are displaying a VDU character test and a game called Hanoi. All using character graphics rather than pixel graphics.
> At the bottom is a memory board with a staggering maximum of 256K of memory. Since they were 19" racks the board is 18" wide by 24" long. (EEK)
> The point being that these were quite easy to work on and fault find. No multi-layer boards in those days and tracks you could solder.
> ...


Hi Kris,

The TRS80 sadly wasn't a Heathkit, it was sold by Tandy or Radio Shack as it is in the States. That picture looks a lot like the later series of the TRS80. I've got an original first generation TRS80 in my loft. The keyboard was later upgraded to have a numeric keypad and later I added an expansion interface for more memory that the green monitor sat upon! I started off by loading programmes on cassette tape but that never worked well so in frustration I upgraded to two floppy disc drives..which cost a fortune then even by todays standards. That machine taught me basic machine language as well as 'Basic' itself. 
I believe it all still works but the last time I plugged it all together was about 5 years ago. It earn't the nickname of Trash80 mainly due to the first generation being very unreliable.
I'm hanging on to it hoping one day it may be worth a bit as a curiousity piece (==D)


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## K urgess (Aug 14, 2006)

Sorry, Mike. Wrong number. Grey matter needed stirring. Thanks for that.
This was the one it was based on - http://www.pc-history.org/heath.htm
I think Digico changed it to Z80s because it was easier to get at the time and probably cheaper.
The operating system of choice at the time was CP/M until DOS type systems were developed. Which may be another reason for the Z80 CPU. Intel chips had a different instruction set.
I always thought it was a bit like the VHS/Betamax battle and what we see today with the various Blu-ray type video systems. Bill Gates won in the end.
PC-DOS, DR-DOS, MS-DOS, etc., etc.
Believe me, it ain't gonna become valuable. Even the Digico museum at Bletchley Park, who I believe haven't got one, don't want mine. (Sad)
http://www.digico-computers.com/

Kris


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## jaydeeare (Feb 5, 2008)

The first computer I ever had any dealings with was the commodore PET (http://www.commodore.ca/products/pet/commodore_pet.htm).

First one I ever actually bought was a Commodore 64. I learnt programming on this and never looked back since. Best buy I ever made. Bought a second had printer (MP-80 I think it was), then Mini Office 2. With these I learned the basics of spreadsheets and word processing. Came in very handy for future jobs.


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## BobClay (Dec 14, 2007)

I've still got an Oric around here somewhere (6502). I gave the ZX80 kit built machine to a young lad I knew who went off to form a pop group called ALTERN8. 

I doubt the ZX80 had anything to do with that (at least I hope not).

I sailed with a Chief Engineer once who decided to try and write a stock storage program on his Spectrum (which in itself defies all understanding). I think he'd got a couple of dozen lines of code in when the lecky downed him looking for an earth.

He might not have appreciated it, but that lecky did him a big favour.


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## BobClay (Dec 14, 2007)

I'm looking for a comment now from those who still do a bit of fault finding down to component level. I'm only looking for a comment, I've got the fault, but I am curious to how modern circuitry is done, which shows how much out of touch I am with it.

My job doesn't call for much of that, hell with computers these days you pump it or dump it. The caretaker at school asked me to look at his TFT monitor (3 months out of the guarantee).

Symptom .... no power ... completely dead. The hardest part is getting into it (talk about a bloody chinese puzzle). So, finally remove power board and find a soldered in mains fuse.. blown. A full wave bridge rectifier, one diode shorted out. All is well but:

Haven't got a diagram, so sketched out the circuitry as best I could. This is how they do it ... mains voltage is applied via the fuse direct to the bridge rectifier. No intervening transformer ! This is followed by a 450v electrolytic capacitor for smoothing, and the resultant DC voltage slapped straight onto the voltage regulation electronics.

What I'm asking is.... this is more like a valve scenario that solid state electronics. DC voltages at 100's of volts applied direct to the regulatory circuit (from which I presume the low voltage stuff for the display circuity is derived).

Is this normal ? ..... if so, boy am I out of touch. 

I can get a replacement rectifier .... and a bloody soldered in fuse (what a naff idea !) ..... and inline circuit testing as best I can with the meter suggests nothing further on has gone down. The shorted out diode on the bridge (which is rated to 650 volts) went down and pulled the fuse is my assumption.

I can't wait to get back to 'pump it and dump it'.

(Whaaa)


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## donald h (Aug 24, 2005)

As a baby electrician in the RN in the early 1970s, one of my jobs was working on the gunnery control Medium Range System Mark 3. A large double compartment housed the main frame computer and other wizardry where all the various inputs from external sources throughout the ship were fed into banks of synchros and servos controlled by rows of valve drawer units.
This system chuntered away constantly but gave a computed output solution which was then fed away to further banks of valve drawer units which ultimately controlled movement of the main ship`s guns fore and aft and pointed them in the right direction, allowing for own ship`s movement, speed, target`s range, speed, height, direction, whether coming towards, going away or crossing, wind speed and direction, shell ballistics and a host of other influences.
Every single valve in the system had to be removed for planned maintenance on a regular basis, taken up to the workshop facility and individually bench tested. Anyone who has had to do all this will know that it wasn`t just a case of checking all the base prongs, but also the heaters and then the overall performance. It was a long drawn out job when you had upwards of thirty or forty valves to check.
I for one was quite glad that technology did advance for that reason alone!! By the time I left the RN, the same control system was contained inside a cabinet about the size of a fridge.
regards, Donald


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## BobClay (Dec 14, 2007)

> Plenty on the net on how they hackle.


Thanks. I have a handle on it now. I suppose that means even though it's solid state, beware of teethpopping DC voltages !

(EEK)


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## Naytikos (Oct 20, 2008)

Personally I think that whoever invented switched-mode PSUs should have been strangled at birth. A reasonable idea when they work, but absolute murder to fault-find without a cct diagram. Reminds me of the loop-circuits in the Hermes/Argos; now there's another inventor who should not have been permitted to reach old age.


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## K urgess (Aug 14, 2006)

Can you imagine the result of no switched mode power supplies? (EEK)
Carting around a large box of an analogue PSU for your laptop or having a big carbuncle on the back of your flatscreen monitor to house the very warm transformer.
I can't remember the last time I saw a "normal" power supply, even in industrial enclosures.
I did my radar ticket on the Hermes/Argus. No problems, just a bit complicated, is all. [=P]


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## BobClay (Dec 14, 2007)

That may be so. But they are not reliable. Of the hundred or so laptops I've been dealing with in recent years I'd say 30 percent of the power supplies have failed. I have just spent over £800 at work replacing failed laptop PSU's so I'm not exactly impressed by the convenience in size.

The monitor I'm currently trying to get a bridge rectifier for is 15 months old ! .... and let's be honest ... had the user submitted it for repair, the probability is it would have been written off. He'd have been charged a couple of hours labour just for taking it apart and putting it back together, let alone the repair. 

All very well going for small and convenient, but at the expense of reliability...I'm not so sure it's a good deal.


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## K urgess (Aug 14, 2006)

Being a bit of a dinosaur, I hate things I can't get into and at least attempt to fix.
A lot of the laptop supplies are a load of carp. At fifty quid plus apiece they appear to be another of the age-old computer rip-off ideas. Designed with a bathtub curve covering 12 months at the most,
My son's laptop PSU has just failed and he bought a replacement. I bet a pount to a pinch of sh.... that all it was in the old one was that bloody soldered in fuse. It proved totally impossible to get into. (Cloud)
There again the tower PC PSUs are amazing how they continue to work even when choked with dust. [=P]


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## BobClay (Dec 14, 2007)

I'll second that a thousand times over. Bloody laptops are the bain of my life. Awful to work on, vulnerable to even the smallest of shocks, and let's be honest, pretty p1ss poor performance compared to even a moderately priced desktop.

But of course they are convenient, I have one, and when I used to teach they were without doubt very handy. It's mostly an ornament now.


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## sparkie2182 (May 12, 2007)

a friend of mine has a second hand electrical goods shop and does great business in laptops.

many are u/s.........usually power supply.......many are just store bought with the buyer thinking they have comparable performance to a desktop.


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## K urgess (Aug 14, 2006)

I used to take laptops out and use them in car parks, factories and airports programming PLCs. 
I wouldn't take my current Acer out in the car let alone into any sort of cold weather. [=P]
It normally just gets used when I want to look something up or watch a DVD away from the PC.
I have a Sony Vaio that's quite old and an IBM Thinkpad that's not quite so old and you can see the reduction in robustness as you compare the three.
My daughter's MacBook on the other hand is a completely different kettle of fish. 
I suppose quality comes with quantity, of money that is. [=P]


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## BobClay (Dec 14, 2007)

mmm I'd have to second that too. My old laptop is a Sony Vaio, and in all fairness it's never let me down, but like you say, it does feel a bit more substantial that some of the new Dells and Toshibas I work on in the job. It's a bit slow, but very handy for wandering around the school checking the signal strength of our wireless coverage.

I'm on the second power supply (I've had it about 5/6 years). But everything else is original. I've only seen a couple of MacBooks (some of the richer teachers have bought their own), and yes they do seem better made. But as you say, they are a bit pricey. I don't know anything about their reliability.


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## BobClay (Dec 14, 2007)

After more years than I care to remember I got de-soldering and soldering on the powerboard for the school caretaker's monitor today and popped in the bridge rectifier. Couln't get the axial solder-in fuse I needed, so codged in a normal cartridge fuse with a bit of 'on the fly' soldering. Good old Oceanspan type repair ..... (*)) 

Nice to see the monitor strike up afterward (the nightmare of putting it back together again, fiendish types those Chinese). Makes a change from failed hard drives/RAM chips/corrupted Windows registries/network problems and all the other parephenalia we get day in day out. 

And I managed it with only a couple of small burns from the iron :sweat: 

Ah well ... back to reality....


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## K urgess (Aug 14, 2006)

A definite feeling of satisfaction, eh Bob. (Thumb)

The old skills are the best skills.


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## jaydeeare (Feb 5, 2008)

Can't beat a bit of improvisation either.


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## BobClay (Dec 14, 2007)

mmmmm .... I must admit I was a bit curious about that 807 lurking in the back of the flat screen monitor ..... .... but I thought 'it's glowing, so leave it alone...'


(Smoke)


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## Naytikos (Oct 20, 2008)

I've not had much to do with lap-tops, but isn't that 807 the source of illumination for the display?


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## mikeg (Aug 24, 2006)

The 807 is far too good just as a source of illumination  Let's have a bit of respect for this _venerable veteran valve_.
(Smoke)


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## K urgess (Aug 14, 2006)

The 807 must be one of those little things the manufacturers add to turn the bathtub curve into more of a "U" curve.
Guaranteed early failure and replacement.
It probably only clicks in at the same time as the cooling fan so that you don't notice. [=P]


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## BobClay (Dec 14, 2007)

Luv the name though ..... 'Beam Tetrode.'

Sounds like something out of Star Trek.

[=P]


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## K urgess (Aug 14, 2006)

Specially designed to get summat for nowt. (?HUH)
Weren't they the ones that had a negative resistance curve in the characteristics.(EEK)
Also known as a "kinkless tetrode" according to Danielson & Mayoh.[=P]
But weren't 807s just straight tetrodes?


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## trotterdotpom (Apr 29, 2005)

Of course, Bob, how could you pass through a "space charge" without a beam tetrode? Recently I heard that Mr Sulu married another bloke, but I like to think he saved his "secondary emission" for Lt Uhura.

John T.


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## trotterdotpom (Apr 29, 2005)

Pretty sure they were beam tetrodes, Fubar. Mind you, until recently I thought Mr Sule was a straight tetrode - he turned out to be anything but "kinkless".

John T.


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## Gareth Jones (Jul 13, 2007)

I was once told that the Americans produced large quantities of unwanted 807's in the 50's, and that this was the reason that Marconi's designed them into the Oceanspan - they were dead cheap !


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## K urgess (Aug 14, 2006)

You're right, JT. (Thumb)
Danielson & Mayoh don't mention them being beamers in their description of the Oceanspan but Pinnacle's "Pocket Chart for the Service Engineer" (EEK) lists them as output beam tetrodes priced at £1.5.0d.
Oceanspan VI had 5 807s, 3 EF50s (usually red canned ex WD or AM) and the good old STV280/80.


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## BobClay (Dec 14, 2007)

As I remember it the tetrode valve had the negative resistance curve due to seconday emission. The beam tetrode overcame that problem by concentrating the current into a beam using cathode connected plates.


"I'm sorry Captain, but the dilithium crystal has melted, and we havenae got a spare.... and the 807's have come out in sympathy."

"Are you telling me Scotty that a huge stellar battle cruiser is dead in space because of a bloody 807.."

"Aye Captain, that's about the cut of it."

"Ya fired ya useless git."

[=P]


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## jaydeeare (Feb 5, 2008)

Marconi Sahib said:


> Oceanspan VI had 5 807s, 3 EF50s (usually red canned ex WD or AM) and the good old STV280/80.


If they were ex WD/AM, they would probably have had a CV Number - CV Common Valve. Any idea what it was?


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## K urgess (Aug 14, 2006)

EF50 = VR91 (AM 10E/92) = CV1091 (Thumb)


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## wireless man (Jun 16, 2008)

Is the kinkless tetrode valve the same as the high gain pentode valve used in German aicraft Knickebein receivers in the last conflict.
Sorry just wondered


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## mikeg (Aug 24, 2006)

Marconi Sahib said:


> The 807 must be one of those little things the manufacturers add to turn the bathtub curve into more of a "U" curve.
> Guaranteed early failure and replacement.
> It probably only clicks in at the same time as the cooling fan so that you don't notice. [=P]


The 807 despite its earlier failings lives on - google '807 amplifier' and you'll find a keen following by the audio fraternity and surprisingly the valves last well in that environment when they didn't at sea as RF output and modulators etc (or was that down to the circuit design - I wonder......)


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## Naytikos (Oct 20, 2008)

Everyone seems to have a fragment of this story; fascinating.
The version I heard was that, indeed Marconi's had a warehouse full of 
EF50s left after the war and, as has been mentioned, could get US surplus 807s. This version also has it that the Oceanspan was actually a development of a wartime aircraft Tx. 
It always puzzled me that they used a mix of British and American valves/tubes; cheap availability has to be the likely answer. "Here's some components, now design a transmitter to use them up", or something like that.


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## Gareth Jones (Jul 13, 2007)

Naytikos said:


> Everyone seems to have a fragment of this story; fascinating.
> The version I heard was that, indeed Marconi's had a warehouse full of
> EF50s left after the war and, as has been mentioned, could get US surplus 807s. This version also has it that the Oceanspan was actually a development of a wartime aircraft Tx.
> It always puzzled me that they used a mix of British and American valves/tubes; cheap availability has to be the likely answer. "Here's some components, now design a transmitter to use them up", or something like that.


 This is very interesting, and hints at something I've always wondered about - The famous RAF T1154 wartime transmitter ( as used on Lancaster Bombers) had Identical knobs to the Oceanspan, same colours even. Yet the T1154 didn't use 807's.


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## jaydeeare (Feb 5, 2008)

Marconi Sahib said:


> EF50 = VR91 (AM 10E/92) = CV1091 (Thumb)


Thanks!

CV1091 rings a bell with me. it ws in general use just about everywhere!

Also the CV303 (I think) which was a Power Triode in Power Suppies with the anode cap at the top of the valve. Very prone to microphoning. Most of the time, a quick turn on the screw of the cap would do the trick - usually found by giving it a tap and watching the O/P dance around like the clappers!


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## mikeg (Aug 24, 2006)

I remember the ubiquitious CV1091 well. The story was that the original EF50 when used in RAF aircraft vibrated out of its base so the screw down cap to valve base was developed by the RAF. Can't imagine how it perform in the air cos they didn't last long on the ground. Also was used in radars, tellys..you name it, its been there (==D)


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## BOB GARROCH (Oct 10, 2008)

If you want to see how Star trek communicated, Google "Motorola Mesh". I always wondered how Scotty could check his warpdrive from his handheld device and how did they communicate on other planets. Mesh is the answer the most amazing communcations system ever invented. I am busy installing a system in a mine in SA


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