Old Time Electrical Engineering

[Sir Nibble]

As a first year university project we were given the circuit diagram for a multimeter and asked to calculate the values for all the resistors. Once our calculations had been checked we were given the kit of parts and told to go away and build it - a first lesson in soldering for many of my fellow students. We then had to do various tests to determine the accuracy of the different ranges.

 

I kept it for years, until leaving it for too long on a damp unoccupied boat led to internal corrosion and it stopped working.

University!? I did that in tech college.

[Keeping Up]

Well, in my post #3 I was offering my AVO 8 free of charge, having twice on this forum offered it for just £5 to people who said they wanted one and got no response whatsoever. I even tried it on eBay a couple of years ago with no reserve, and got no bids at all. If they are fetching good money again maybe I'll try eBay a second time, but as a man of my word I'll stand by my original offer to the OP (which seems to have been ignored) for 24 hours first.

 

Allan G3XJO

[WotEver]

Well, in my post #3 I was offering my AVO 8 free of charge, having twice on this forum offered it for just £5 to people who said they wanted one and got no response whatsoever. I even tried it on eBay a couple of years ago with no reserve, and got no bids at all. If they are fetching good money again maybe I'll try eBay a second time, but as a man of my word I'll stand by my original offer to the OP (which seems to have been ignored) for 24 hours first.

 

Allan G3XJO

Nice one, Allan. I too noticed that OP appears to have ignored your kind offer.

[16csvt]

Mirrored scales, shunts and multipliers.

Takes me back more years than I care to remember!

 

Now, I've used a mirror galvo, where the pointer is a reflected beam of light, so the pointer could be as long or as short as one wished, with nil mass / inertia to boot.

I don't recall a ballistic galvo.

I'm intrigued.

 

Regards

 

Kevin

[dmr]

Mirrored scales, shunts and multipliers.

Takes me back more years than I care to remember!

 

Now, I've used a mirror galvo, where the pointer is a reflected beam of light, so the pointer could be as long or as short as one wished, with nil mass / inertia to boot.

I don't recall a ballistic galvo.

I'm intrigued.

 

Regards

 

Kevin

 

Essentially a standard meter movement but without the return spring .. whilst a current flows the pointer keeps advancing, so measures charge..

Interesting as it could also be viewed as an amp-hour meter. I remember it was quite hefty so maybe it had a bit of inertial mass, but then again a few years ago all instruments were a bit on the heavy side.

 

Keeping up..... As for AVOs, I think the exact model can have an influence on price so do check before you give stuff away, I think the 7 was the valuable one.

Had a Christmas "meeting" with ex work mates last week and we discussed the stuff some of us have hoarded (Nagra Tape Recorders in particular) and I proposed that prices of some old stuff are now actually falling.... once stuff gets to an age where the people who used to use it are dead (or at least too old to collect stuff), then the price will fall. Few youngsters want to collect things they have no connection with. When work folded we sold a lot of stuff on eBay especially instrumentation tape recorders, and these almost all went to blokes in their 50's and 60's.

 

.............Dave

[Chewbacka]

I had a vague memory from my physics teacher telling us about the ballistic galvo, but I could not remember But I could google it. Fascinating and clever how analogue methods were developed to measure stuff.

[dmr]

I had a vague memory from my physics teacher telling us about the ballistic galvo, but I could not remember But I could google it. Fascinating and clever how analogue methods were developed to measure stuff.

 

I 'spose the ultimate was the analogue computer. They never really caught on though, maybe the games weren't good enough, or maybe its cus they didn't do facebook.

 

..............Dave

[cuthound]

Anyone remember using a valve voltmeter? They had a very high input resistance, so influenced the circuit they were connected to less, giving a more accurate reading.

 

I also remember using the first digital Avo in the early 70's, red display and piano keys (like early cassette tape recorders) to select function and range.

 

Until we moved recently I still had the decade resistance box made at school during physics and metalwork lessons.

[jonesthenuke]

I realised a few years ago, when the likes of Ebay was first starting, that old electrical instruments were getting rarer but could still be found. The brass, wood construction etc is attractive in both an aesthetic sense and technically.

 

For AC and DC measurements you want one of these, state of the art 100 years ago and probably only owned by universitys and National Standards organisations

 

http://eolstoragewe.blob.core.windows.net/wm-418498-cmsimages/MuseumImage/Image63_350.jpg

 

Its about 3 feet long and currently resides under the bed. Bought for less that you apparently pay now for an AVO 8

 

PS AVOs were originally the "Automatic Coil Winding Co" (ISTR) and I have and AVO8 of the vintage too somewhere.

[WotEver]

I also remember using the first digital Avo in the early 70's, red display and piano keys (like early cassette tape recorders) to select function and range.

I remember them well. They were only for bench work though. We used to use Avo 8's while working our way through banks of 6ft racks of analogue boards to make ginormous flight simulators.

[billh]

Anyone remember using a valve voltmeter? They had a very high input resistance, so influenced the circuit they were connected to less, giving a more accurate reading.

 

I also remember using the first digital Avo in the early 70's, red display and piano keys (like early cassette tape recorders) to select function and range.

 

Until we moved recently I still had the decade resistance box made at school during physics and metalwork lessons.

Still occasionally use a Marconi VVM, seventies vintage. I have a couple of wood cased Salford Electrical Instruments (GEC) VVMs dated from 30's or 40s, unrestored but must be quite rare now. Also a brass cased (black painted) Philips with Ct8 type valves and German? writing in it.

On the DVM theme, I have a Solartron voltmeter from about 1960 which has a digital readout , the display is done by switching lamps at the back and projecting the numbers through a stencil onto a panel on the screen. Hybrid technology with ME1400 electrometer valves in the front end- not strictly digital except for the display! All this stuff is huge compared with current technology.

Bill

[cuthound]

All this stuff is huge compared with current technology.

Bill

Yes, I remember having to take a van load of instrumentation to commission generators, UPS' etc. By the time I retired you only needed a small toolbox to carry all the instrumentation (half of which interfaced with a laptop to record or display).

[FORTUNATA]

Any ammeter with a resistance of 100 ohms belongs in the bin because it certainly not an ammeter.

!00 Ohms is very often quoted in the book for the ammeter. However, I can tell you the schematic is mind-bogglyingly confusing. After a good deal of time last night spent baffled by the explanations, I concluded the writer of the book is guilty of being vague and missing out details. Where he says, "left hand socket" it's probably on the right hand side (the schematic of the meter is going to be opposite if it's turned face over).

 

It got a good deal worse when he recommends using a 1.5 battery to set resistance wire so it reads exactly 0.005 amp and then quotes 250 Ohms (I got 300 Ohms but assume he implies maybe 50 Ohms for the meter??) If so, why not elaborate? Personally, having finally deduced he's simply using various lengths of resistance wire as shunts between the meter terminals via a socket and plug circuit, surely It's easier just to work it all out mathematically and buy the exact resistors?

 

At that point my brains were "frazzled"

 

 

I won't be building this meter but am using it as a guide as to how they made stuff like that. One gripe is it maxes at 200 volts. Really I need up to 500 volts.

 

All of this can be seen in light of the good old ammeter shunt, favoured by boaters for decades. I was thinking of various possible ways to make a shunt that will read up to 200 amps. Commercial ones tend to be around 75 or 100 millivolts.

 

 

 

 

 

 

[FORTUNATA]

Anyone remember using a valve voltmeter? They had a very high input resistance, so influenced the circuit they were connected to less, giving a more accurate reading.

 

I also remember using the first digital Avo in the early 70's, red display and piano keys (like early cassette tape recorders) to select function and range.

 

Until we moved recently I still had the decade resistance box made at school during physics and metalwork lessons.

There is a simple schematic for a valve tester which is a lot easier to make than the meter. The only question I had was where do you get the valve holders from as there were so many types, 7 pin, 5 pin Octals and so on.

 

I did make myself a dim bulb tester last year which I found to be awesome. I've even heard these can be converted into car battery chargers. At first I didn't think my dim bulb tester worked till one day I plugged something in that had a slight leak and, bingo, the dim-bulb tester glowed orange. It simply soaks up any small short circuit, takes heat away from the appliance and lets you know there is fault. It turned out to be a tiny bit of wire insulation I needed to tape.

 

 

[IanD]

Any ammeter with a resistance of 100 ohms belongs in the bin because it certainly not an ammeter.

Yes it is if it has 100uA full scale, this means a voltage drop of 10mV across the 100ohm coil.

 

One of our university practicals in 1978 was to build and calibrate a multimeter, which I've still got. The amps settings put smaller and smaller resistors in parallel with the 100uA meter, always maintaining 10mV voltage drop at full scale -- so 1 ohms for 10mA, 0.1ohms for 100mA and so on. The volts settings put bigger and bigger resistors in series with the meter, always maintaining 100uA current for full-scale -- 10kohm for 1V, 100kohm for 10V and so on. This would be a "10kohm/V" meter, higher quality (more sensitive) meters would need less current -- I think the AVO 8 was 20kohm/V, in other words the basic meter had a 50uA full-scale.

[BruceinSanity]

We're onto p2 and no one's mentioned the Post Office box which I vaguely recall from school physics lessons.

 

Any former users out there?

 

https://en.m.wikipedia.org/wiki/Post_Office_Box_(electricity)

[Batavia]

 

Essentially a standard meter movement but without the return spring .. whilst a current flows the pointer keeps advancing, so measures charge..

Interesting as it could also be viewed as an amp-hour meter. I remember it was quite hefty so maybe it had a bit of inertial mass, but then again a few years ago all instruments were a bit on the heavy side.

 

The moving part of a ballistic galvanometer has a much higher moment of intertia than an ordinary galvanometer and without the spring, the deflection is a short-term time integral of current -so it essentially measures charge.

 

I can vaguely recall using it in physics experiments during the late 1960s, doing something with flipping coils in magnetic fields. I will see if I can find my copy of GAG Bennett's "Electricity & Modern Physics" textbook, which might explain everything (or possibly not - but it was an improvement on Mackenzie's "A Second Course In *******" - anyone remember them?).

 

Someone mentioned analogue computers. In the early 1970s, I built a task-specific one, with 800 op amps and 100 analogue multipliers. It was much faster for solving sets of differential equations that trying to do it digitally on the CDC 7600 but clearly the end of an era!

 

Chris G

[FORTUNATA]

Yes it is if it has 100uA full scale, this means a voltage drop of 10mV across the 100ohm coil.

 

One of our university practicals in 1978 was to build and calibrate a multimeter, which I've still got. The amps settings put smaller and smaller resistors in parallel with the 100uA meter, always maintaining 10mV voltage drop at full scale -- so 1 ohms for 10mA, 0.1ohms for 100mA and so on. The volts settings put bigger and bigger resistors in series with the meter, always maintaining 100uA current for full-scale -- 10kohm for 1V, 100kohm for 10V and so on. This would be a "10kohm/V" meter, higher quality (more sensitive) meters would need less current -- I think the AVO 8 was 20kohm/V, in other words the basic meter had a 50uA full-scale.

By the start of the Forties it seems 10 Milliamps was pretty common. Sometimes 30 Milliamps. Cost was a major consideration. According to my book, not all homes yet had A.C. supply. Not all supplies were at 50 Hertz either. The big HT batteries were around 120 volts D.C. It was considered any test with a draw of 30 Milliamps was a costly affair. Batteries had to be recharged periodically. The DIY meters may have used just 5 Milliamps full deflection. Usual resistances were 1000 R, 10000 R and 100,000 R.

 

Resistances were also tested with a battery and an ammeter. You could simply get the resistance in Ohms through Ohms law. They had to take care not to apply full voltage at first in case the resistor was very low and below value.

 

It's good fun reading old engineering books. I may get some more from E-Bay. I liked the simplistic capacitor test which was to simply bridge terminals with a screwdriver for a second. I can verify you do get a very big spark and it does make you jump.

 

 

 

 

[dmr]

Someone mentioned analogue computers. In the early 1970s, I built a task-specific one, with 800 op amps and 100 analogue multipliers. It was much faster for solving sets of differential equations that trying to do it digitally on the CDC 7600 but clearly the end of an era!

 

Chris G

 

Yup that was me.

Final year project at uni and worth 40% of the finals (a good hands-on degree). I had spent ages building loads of electronics to control a huge DC motor. Right at the end my supervisor said "you really should do a computer model too" . I had visions of hours of Fortran on the mainframe, or struggling with the departmental PDP8, and must have looked a bit downcast. He said "Don't worry, there;s an old analog computer downstairs, you'll get the whole job done in an afternoon". He was correct!

 

..............Dave

[Stevec]

Fortunata post 38: "I was thinking of various possible ways to make a shunt that will read up to 200 amps. Commercial ones tend to be around 75 or 100 millivolts."

 

How about this design from Jerry Radcliffe N8KLX in June 2012 in the QST magazine.

 

Use a bolt with six nuts (3 on each end. Outer nuts connect battery to load, Inner nuts connect leads for meter.

 

To calibrate the shunt us a battery or PSU - a suitable load and a meter that can measure amps

 

1.Connect the meter in series with the load and note the amps

2. substitute the shunt for the meter.

3. Put the meter onto the milivolt scale and place across shunt.

4.Adjust the distance between the nuts to get milivolts same figure as amps noted in step 1

 

note accuracy effected by temperature rise if high currents - so suitable size of nuts & bolts needed

 

Stevec

[Batavia]

 

the departmental PDP8

Ah! a PDP8 - the most perfect small computer, especially the model with the wood-effect Formica doors. The world started to go to pot when DEC brought out the PDP11 (but the PDP9 and PDP15 were interesting machines)!

 

I still have my copies of "Introduction to Programming" and "The Small Computer Handbook", published by DEC c.1969 and which must have been given away by them in the tens of thousands. Anyone need some Assembler written for a PDP8 or a PDP15?

 

Chris G

[Chewbacka]

Ah! a PDP8 - the most perfect small computer, especially the model with the wood-effect Formica doors. The world started to go to pot when DEC brought out the PDP11 (but the PDP9 and PDP15 were interesting machines)!

 

I still have my copies of "Introduction to Programming" and "The Small Computer Handbook", published by DEC c.1969 and which must have been given away by them in the tens of thousands. Anyone need some Assembler written for a PDP8 or a PDP15?

 

Chris G

I remember having to buy a replacement core memory board (ferrite cores) for a PDP11 (think it was 11) it cost about £2k and needed 2 hands to lift it. This was for an early 'pick & place' machine. Beautiful workmanship and I still remember looking at all the little ferrite cores in an array.

[keble]

On the DVM theme, I have a Solartron voltmeter from about 1960 which has a digital readout , the display is done by switching lamps at the back and projecting the numbers through a stencil onto a panel on the screen. Hybrid technology with ME1400 electrometer valves in the front end- not strictly digital except for the display! All this stuff is huge compared with current technology.

Bill

Solartron, there's a blast from the past! Great Nixie tube displays.

Trying to remember other test equipment companies: Keithley and HP which are still going.

What others?

[billh]

Solartron, there's a blast from the past! Great Nixie tube displays.

Trying to remember other test equipment companies: Keithley and HP which are still going.

What others?

A quick look in my stores:

 

Cambridge Instruments- (thermo couple bridge)

Fluke- multimeter

Wayne Kerr bridge ( no jokes please)

STC engine analyser

Heathkit Daystrom signal generator

Bradley Electronics - precision voltage source

Racal-Dana frequency meter

Muirhead- frequency analyser

Marconi Instruments- various

Advance Electronics- signal generator

Farnell- PSUs

Tektronix

Telequipment -o'scope

Griffin & George -scalar

Airmec - stabilised PSU

Samwell & Hutton -TV wobbulator (!!!)

Evershed & Vignoles-meters

 

 

 

Some of this gear is 1950s Ferranti Bloodhound Missile testing stuff , do you remember that and the scandal associated with it?

Bill

[Chalky]

I have a collection of electrical manuals called "Modern Electrical Installations". It's in 5 volumes and its dated 1897 - yes 1897. One volume deals with items like how to make cables with lead and bitumen insulation. Another has items such as using a tank of water as a resistance to dim lights. There's another volume that deals with steam engines so you can run your generator!

Most / all of the kit mentioned earlier was just a pipe dream.

Ah! a PDP8 - the most perfect small computer, especially the model with the wood-effect Formica doors. The world started to go to pot when DEC brought out the PDP11 (but the PDP9 and PDP15 were interesting machines)!

 

I still have my copies of "Introduction to Programming" and "The Small Computer Handbook", published by DEC c.1969 and which must have been given away by them in the tens of thousands. Anyone need some Assembler written for a PDP8 or a PDP15?

 

Chris G

I still have my Microtan 65 from 1978. One of the last rack based home computers. I started programming on Nascom 2s and learned Fortran and Pascal on the Harris mainframe at college. Fortunately Harris no longer make computers.