A Handy Headphone Matching Unit

[pwdrive]

I don't think anyone's pouring cold water on Spark's achievement, his practical skills look pretty good to me, model ships and all, what has been pointed out and quite rightly so is the downside of using the type of transformer that was used, that led to a bit of "theoretical" about transformer matching/impedance etc, nowt wrong with that either.

Lawrence.

[Terry]

With me, it is no longer an obsession, and I only gain pleasure from experimentation, trial and error, and the theory can "go hang!"     I can go for weeks or months without even thinking about radio.  

I don't think anyone who posts here does anything in this field other than for pleasure, so I'm with you on that.

However, a lot of the information in this thread may well be of use to someone else of limited technical knowledge who is considering doing something similar.

"In any closed circuit of constant temperature, the ratio of voltage applied, to the current set up by that voltage is constant.   That constant is known as the resistance of the circuit!"  

I think the version I was taught is easier to understand: "When the temperature is constant, the potential difference across the ends of a resistance is proportional to the current flowing through it"

I would guess that this version precedes yours as it seems to have been written before the names of Volt, Ampere and Ohm were defined and adopted.

Many learn Ohm's law without the first part relating to temperature - or choose to ignore it - which they can later find very puzzling!

[Sparks]

Terry,
I think my version of Ohm's Law was written for my particular college (Wray Castle) in 1958 when it opened as a radio training school.    I joined in spring 1959.     They may have thought up that Ohm's Law version themselves, or got it from a textbook - don't know!
Anyone trying to build practical radio receiver without any knowledge these days may well burn their headphones out      The first circuit I ever built, showed the headphones connected between the anode and HT positive.   It came from a very old textbook   (The HT was only 22.5V because that was the highest voltage batty I could afford).      I knew nothing about matching, but in my case, it didn't matter, because my headphones (ex RAF surplus) were the standard 4,000 Ohm types, and worked fine.    As headphones all seem to be low impedance these days, it may burn them out if they don't use a matching transformer!    
I really wonder if any young people try building valve sets, or even transistor sets, these days.     I have produced  a few instructional downloads, but there is very little interest in them.    Although one or two that did get them, had no trouble in getting them to work.  
I would have liked to have written a practical radio construction book, but abandoned the idea because of a general lack of interest.     Repairing valve radios is not much of a challenge for me, and I am not into cabinet restoration - only interested in the "works."       I have hopes of finding an old valve radio embedded in the mud of the River Ribble, and if I did, I would retrieve it, and make it work again.   In the 50s, I was often finding old radios in the river, and that is what sparked my interest in the first place!
We are the same age, apart from a few weeks!  
Bob  

[Crackle]

"When the temperature is constant, the potential difference across the ends of a resistance is proportional to the current flowing through it"

Or more simply put, and as my dad taught me when I was about 9.
"Rest equals coffin under earth."

(r=resistance, c=current, e=electromotive force or volts)

Mike

[Terry]

A neat trick I learned somewhere was, if you use E for voltage, I for current and R for resistance and put them into a triangle in alphabetical order, deleting the unknown automatically leaves the correct formula for calculating it!

If you prefer V for voltage, VIR as in Vulcanised India Rubber works too.

More recently you could have used VCR as in Video Cassette Recorder - but they were only a pipe dream when I learned the original (at school, if my memory is right).