Old Time Radio Engineers

[Nowhere-Man]

Absolutely right; 100V will cause 5mA to flow in a 100k resistor.

Oops!
I have spotted a mistake in the calculations.
It aught to read 1mA and not 5mA.

Oops indeed - thanks for pointing that out! Clearly a brain-fart, but no idea how I missed it when I proof-read. I'll correct the original post to save confusion, but happy to leave this here to show that I'm human

Making simple maths mistakes is dead easy when you're typing. In the past I've made posts on websites and later discovered I'd made a blunder. Fortunately, sometimes nobody notices so I had time to go back and correct my mistake.

One interesting case is Rick McWhorter's book on All American Five Radios. Apparently it's riddled with errors in Ohms Law so Rick was savaged by critics on Amazon in the book reviews. At the time, I'd been tempted to join Amazon and add my own comment to defend Rick as it seemed clear to me they were mistakes of the absent minded variety. For example, the guy is at home with a house full of kids and his wife and typing his book on Windows. One of the kids spills his orange juice so that leads to a hasty calculation and later out it goes to print!!At any rate, there were some guys who were doing a degree in electronics and he basically slammed Rick McWhorter on the Amazon book review. It was pointed out the Ohms calculation had been arrived at by multiplication instead of division and, even worse, "sine wave" had been spelled as "sign wave". He was also slammed for talking of "positive bias" on a grid of a Triode. True, but I think we all know he meant "a negative bias that becomes more positive". Of course, I do agree it's a real pain if a writer doesn't have his book proof read.

I recall in another book I found a whole mains drop resistor circuit in an ACDC radio that was way off because the writer started out with 250 volts supply and then based the other resistances on 230 volts A.C.

[Nowhere-Man]

O.K. Mark, I just read your comments on voltage and series resistors - I'll probably print out the page here at the library and then stick it in my textbook for reference. I hope you understand I'm not being rude when I seem to delay responding directly to explanations because sometimes I have to do this later on. Let's say I get about 4 or 5 posts but only have an hour and bit, plus e-mails to sort through.... Anyway, thanks for your help and patience.

Hi NM,

No problem at all - I understand the time pressure at the library and everything.

It reminds me of the days before having broadband at home, where you'd set aside a couple of hours for the computer. First, dial up to download the messages and grab all the web pages you wanted to read. Then, once off-line, respond to all the emails and read all the web pages that you got earlier. Then dial up again to get the messages sent and follow any new thoughts. It was very different.

I held off getting broadband for as long as possible because I knew it would take over. And it certainly does. But of course, you can't be without it!

I do have mobile internet on anew Blackberry phone someone gifted me but I haven't topped it up yet. I think it's on EE but the lady who gave it me reckons I could put in a 3Phone Sim. However, for now, internet time has been hugely cut down. Maybe for a time it's a good thing. I feel lately like I'm in a Time Warp. For example, last night I was simply listening to Radio Five Live on a 1947 ACDC radio. It felt kind of weird listening to a political debate on a radio that would have been used to report about the construction of The Berlin Wall.

As to the book. I did come across a way to measure the inductance of a coil using an electric buzzer and a calibrated crystal radio. I wasn't sure where the book was going with the maths calculation, though. I know how to calculate a resonant frequency using Pi and division by 1000000, plus using square roots but, unfortunately, the book was vague and it helps if they give an illustrated example. Anyway, you use headphones to tune into the buzzing and that should give a calibration mark on the dial you can use perhaps with the fixed capacitor to work out the inductance. Sadly it gives too little detail.

[ppppenguin]

If you're publishing a book you owe it to your readers to do basic proof reading. It's not a like a forum post which is often done in haste. I don't know Mc Whorter's book but if it's as bad as you say then he deserved all the criticism he got.

Many GVR members will have a copy of Gerry Wells' autobiography**. This is a wonderful book, Gerry's voice leaps from the page. But it's marred slightly by numerous typographical errors. This is despite having been edited by a professional. It appears he edited for sense and continuity while keeping Gerry's unique voice intact but neglected to do the basic copy editing. Even a spill chucker wouldl have picked up many of the typos. In this case the reader isn't being mislead, unlike in McWhorter's book where an inexperienced reader might make serious mistakes as a result of what he's seen.

**Obsession: A life in Wireless. Copies should still be available at BVWS events and from the Vintage Wireless Museum.

[Mark Hennessy]

As to the book. I did come across a way to measure the inductance of a coil using an electric buzzer and a calibrated crystal radio. I wasn't sure where the book was going with the maths calculation, though. I know how to calculate a resonant frequency using Pi and division by 1000000, plus using square roots but, unfortunately, the book was vague and it helps if they give an illustrated example. Anyway, you use headphones to tune into the buzzing and that should give a calibration mark on the dial you can use perhaps with the fixed capacitor to work out the inductance. Sadly it gives too little detail.

Gosh - that sounds like a complicated way to do it!

Mind you, I can't think of an obvious way to do it with minimal test gear. A signal generator and a volt meter are a sensible minimum, but back then these would have been expensive tools. We're lucky that today, £10 or thereabouts gets one of those magic "test everything" component testers from China.

[Nowhere-Man]

If you're publishing a book you owe it to your readers to do basic proof reading. It's not a like a forum post which is often done in haste. I don't know Mc Whorter's book but if it's as bad as you say then he deserved all the criticism he got.

Many GVR members will have a copy of Gerry Wells' autobiography**. This is a wonderful book, Gerry's voice leaps from the page. But it's marred slightly by numerous typographical errors. This is despite having been edited by a professional. It appears he edited for sense and continuity while keeping Gerry's unique voice intact but neglected to do the basic copy editing. Even a spill chucker wouldl have picked up many of the typos. In this case the reader isn't being mislead, unlike in McWhorter's book where an inexperienced reader might make serious mistakes as a result of what he's seen.

**Obsession: A life in Wireless. Copies should still be available at BVWS events and from the Vintage Wireless Museum.

I believe I have found yet another mistake. My book Everyman's Radio is discussing capacitor values in a special chapter. In this maximum and minimum values are suggested for either H.T. filtering or R.F. bypass and so on. The writer then suggests 30 Micro-Microfarads as a limit figure but then writes 0.0003. Now, so far as I can gather, it should be 0.00003. The reason I say that is as follows:

If there are 1000000 picofarads in a microfarad, by the time you get to a thousandth of a microfarad, there ought to be just 1000 picofarads. So, 0.003 ought to be 3000 picofarads? And therefore, 0.0009 is as close as 900 picofarads and nearly 1000 picofarads 0.001. Consequently, 0.0001 = 100 picofarads and 0.00001 10 picofarads.

I think I got this correct, unless my brain is frazzled again!!

I don't think they had picofarads back then so perhaps easier to confuse digits.

Does this make sense?

[pwdrive]

http://www.unitconversion.org/electrosta...rsion.html

Lawrence.

[Nowhere-Man]

As to the book. I did come across a way to measure the inductance of a coil using an electric buzzer and a calibrated crystal radio. I wasn't sure where the book was going with the maths calculation, though. I know how to calculate a resonant frequency using Pi and division by 1000000, plus using square roots but, unfortunately, the book was vague and it helps if they give an illustrated example. Anyway, you use headphones to tune into the buzzing and that should give a calibration mark on the dial you can use perhaps with the fixed capacitor to work out the inductance. Sadly it gives too little detail.

Gosh - that sounds like a complicated way to do it!

Mind you, I can't think of an obvious way to do it with minimal test gear. A signal generator and a volt meter are a sensible minimum, but back then these would have been expensive tools. We're lucky that today, £10 or thereabouts gets one of those magic "test everything" component testers from China.

There is a great way to work out the voltage divider resistances without a current value. I tried it on my trusty calculator. If you have two large resistors and you know the total resistance but not the individual resistances of the divider, it can be done via voltage and proportion. Say the H.T. voltage is 100 D.C. and the anode voltage is 80. The voltage divider must supply the said anode from the source voltage. Simply divide the lesser voltage into the larger voltage. Then divide that acquired sum into the total resistance in Ohms of the divider which will allow two resistance values to be used.

In this book I notice there is a heck of a lot of transformer coupling. It must have been all the rage for a time.

[Nowhere-Man]

http://www.unitconversion.org/electrosta...rsion.html

Lawrence.

Looks like I'm right then. 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. This was gifted to me by a friend ages ago and runs on a small battery.

I tend to do it this way but need total peace and quiet to think it through:

1 Microfarad = 1000,000 picofarads.

0.5 Microfarad will be 500,000 picofarads. (half)

0.05 Microfarad will be 10 less so 50,000 picofarads.

0.005 should be just 5000 picofarads.

To make it easier after that point I just think of the thousandths as tenths of that value so a tenth of a 1000th will be 0.000(tenth)

P.S. I'm not a good mathematician. I do know people who are naturally gifted at maths but I'm not. I had to work hard on maths for radio work so I could at least have some idea but I use a calculator a lot.

[ppppenguin]

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.

[Herald1360]

I don't think they had picofarads back then so perhaps easier to confuse digits.

They did have micromicrofarads, though. I don't think they generally stopped using microfarads until you got below 100pF - point three noughts five (0.0005) uF was easy to deal with but when you got up to four noughts it wasn't too easy on the eye.

Putting in commas as 1/1000 separators might have helped but I've never seen it done to the right of the point. Maybe 'cos to make sense, the first comma would have to be after two noughts