Old Time Radio Engineers

[Terry]

... I typed in 30 Picofarads and it was 0.00003 but the book has a zero less. Not that I try and catch these people out but I tend to automatically run any digit through my pocket calculator so I know where I'm at ...

All these zeros confuse me too and it's far too easy to make an error.  Anyone for 0.000000000003F? I really couldn't tell you without careful counting what that's meant to be ...

Small print on a printed page can be bad enough but on the screen is even worse! I think I have seen the use of spaces to break the series of zeroes into blocks of three - that, at least, would remove a lot of the confusion.

I prefer, though, to start from the smallest value and work up. Correctly done, this produces clear, unambiguous figures with no zeroes to the right of the decimal point and no more than two to the left.

Thus, using preferred values, picofarads are generally used for 1 - 820ρF then nanofarads for 1 - 820nF and microfarads for anything larger. I say generally because, whilst I would write, say, 4.7nF (or, for maximum clarity 4n7) others might prefer 4,700ρF - which is equally clear.

... I tend to use units that minimise the number of zeros though 100nF is a notable exception as 0.1uF has fewer zeros.  Or scientific notation, usually with the exponent as a multiple of 3. If you're writing without superscripts then 30x10^-12F is easily seen as 30pF. Or as you'd enter it on many scientific calculators: 30E-12.

Surely it is easier to write the formula out first, translating pico, nano, micro, kilo and mega into the appropriate exponents as many of these will cancel out leaving a much simpler calculation before you even pick up a calculator?

[ppppenguin]

Surely it is easier to write the formula out first, translating pico, nano, micro, kilo and mega into the appropriate exponents as many of these will cancel out leaving a much simpler calculation before you even pick up a calculator?

Which is what I often do.

[pwdrive]

Me too, never been too good with numbers, did my C&G formulas no problem 1/2piFC, 2piFL etc, it was all the zero's that got me, no calculators as such back then just log tables so I scrubbed out the zeros to the right of the decimal point for C, L etc and scrubbed out an equal amount of zeros to the left of the decimal point for F in cycles etc, made it easier for me.

Somehow I ended up in the A stream at Secondary Modern, lord knows how, consistently bottom in English and not much further off in maths.

Lawrence.

[Nowhere-Man]

All these zeros confuse me too and it's far too easy to make an error. Anyone for 0.000000000003F? I really couldn't tell you without careful counting what that's meant to be.

That's why I tend to use units that minimise the number of zeros though 100nF is a notable exception as 0.1uF has fewer zeros.  Or scientific notation, usually with the exponent as a multiple of 3. If you're writing without superscripts then 30x10^-12F is easily seen as 30pF. Or as you'd enter it on many scientific calculators: 30E-12.

I've often been forced to use an online calculator when in Maplins as I can't work it out without being in total quiet with my calculator. I do have a habit of using large decimal numbers because they work well for multiplication. Of course, my maths is really pretty basic and I only swatted up on it very recently.

I think it does go to show that when you write a book, there is every chance of making mistakes. Rick McWhorter unfortunately had dozens of typos which he'd have spotted if he'd double checked. Last night it seems I found yet another possible error in my Forties book - this time possibly a circuit issue.

I will get back to you all with a question I have on maths. I'll have to photograph the page. There is an equation for the inductance measurement and it has me baffled. It's a simple algebra sum but there is no example to guide me. Normally if they give an example I can figure it out.

I quite like the idea of learning the old ways of doing stuff with milliameters but won't be a martyr to the cause either. In some cases I'll be forced to just use a modern device. Hilarious by the way to see the drawings in the book of the hand-drills! Even calculations as to costs of running the radio by mains (hungry thirties).

[Nowhere-Man]

It's been quite a good learning experience this book. It's more about trying to get an idea how the engineers had to work in that era when society was less industrialised. It seems money and cost was a significant factor and some engineers made their own all-purpose test meters using cigar boxes, sockets and home-made test prods.

Put simply, as I understand it, the way they had to think was like this: If you have a current meter that has a max of 10 milliamps and you want to test that a 1000 Ohm resistor really is 1000 Ohms, you have to start by multiplying the current by the resistance to get the voltage you'll be using. At that point they tended to grab a grid bias battery or an H.T. battery. The idea would be to make a circuit with the battery, meter and resistor to measure current. However, if the resistor happened to be very low due to a fault you didn't know at the time, and you applied the full battery voltage straight away, the current would go way over the limit and screw the meter. So, they simply tried first with, say, 1.5 volt and calculated what the expected current ought to be (if the resistance was 1000 Ohms). Obviously if you thought the resistor was O.K., applied full voltage but it was actually only 100 Ohms and not 1000 ohms, you could get problems as devices weren't fused.

So, basically, it's kind of fun to take a look at how people worked back then. No electric drills or digital testing gear. They even tested variable, moving vane condensers with a light bulb.

[Crackle]

It's been quite a good learning experience this book. It's more about trying to get an idea how the engineers had to work in that era when society was less industrialised. It seems money and cost was a significant factor and some engineers made their own all-purpose test meters using cigar boxes, sockets and home-made test prods.

Sounds like what a lot of school boys probably did back in the 60's, and earlier, if they had hardly any pocket money to buy the items they needed for their electronics experiments and hobby.
Mike

[Nowhere-Man]

I wish this guy who wrote the book was a bit more specific in stuff he explains. I've been trying to work out the DIY All-Purpose-Test-Meter schematic. It has about 8 sockets each side for current or for voltage. What throws me is he is he isn't quite specific enough for me to follow which is annoying. Such as, "Run the test lead through the black ebonite socket" and I'm thinking, "What 'test lead?' and what 'black ebonite sockets?' Maybe he refers to the leads from the ammeter but I'd prefer it to be spelled out so I know exactly where I'm at. I've always lacked the ability to summarise and generalise so I tend to need really specific explanations and I dislike it when something is just pulled out of the hat.

At any rate, I'll carry on and fight the good fight. The writer boasts that his meter is a lot more economical than other test meters as it only used 5 Milliamps whereas the commercial ones of the era often used 30 Milliamps. This latter was thought to be expensive in electrics and battery supply. These people had no concept of being able to use digital meter with a small battery.

So far as I can fathom the whole device relies on resistors that are shunted and those in series for voltage. I've never used my calculator so much as recently. That is, I spent some time adding up the meter resistor with the shunt resistor to get the parallel digit value. Sure, I've done this before in text books but not with any actual goal.

You could call this a bit of a rest from the soldering although I still have a tuning mechanism to string and a cabinet to restore.