Part 6 (1/2)

[Illustration: Fig 21]

One rid is otten to see what happened so he went hos

He shi+fted the battery clip along, starting at _c_ of Fig 22 At the nextlist of readings and hence of points on his proposed road

Minus 10 Volts and Plus 06 Mil-ampere ” 20 ” ” ” 04 ” ”

” 30 ” ” ” 02 ” ”

” 40 ” ” ” 01 ” ”

” 50 ” ” ” 00 ” ”

Then he showed the other23 how the Audion Characteristic would look

[Illustration: Fig 22]

There was considerable discussion after that and it appeared that different designs and makes of audions would have different characteristic curves They all had the sah different sets of points depending upon the design and upon the B-battery voltage It was several s later, however, before they found out what effects were due to the foret much better results with their radio sets

Now look at the audion characteristic Making the grid positive, that is going on the positive side of the zero volts in our er You rerid, when positive, helped call electrons away froer strearid calls electrons away from the filament It can't call them out of it; they have to come out themselves as I explained to you in the fifth letter

[Illustration: Fig 23]

You can see that as we rid more and more positive, that is, make it call louder and louder, a condition will be reached where it won't do it any good to call any louder, for it will already be getting all the electrons away frorid more positive after that will not increase the plate current any That's why the characteristic flattens off as you see at high values of grid voltage

The arrangerid voltage is sie by less than that of a single battery cell I want to show you a hich will

You'll find it very useful to know and it is easily understood for it is so letter

[Illustration: Fig 24]

Connect the cells as in Fig 24 to a fine wire About the middle of this wire connect the filarid If the grid is connected to _a_ in the figure there is applied to the grid circuit that part of the e th of wire between _o_ and _a_ The point _a_ is nearer the positive plate of the battery than is the point _o_ So the grid will be positive and the filaative

On the other hand, if the clip is connected at _b_ the grid will be negative with respect to the filaative depending on which side of _o_ we connect the clip How large the e rid depends, of course, upon how far away from _o_ the clip is connected

Suppose you took the clip in your hand and slid it along in contact with the wire, first froh _o_ to _b_ and so on back and forth You would be ative, wouldn't you? That is, you would be applying to the grid an e m f which increases to so to zero, _reverses_, and increases just as much, only to decrease to zero, where it started If you do this over and over again, taking always the sa on the grid circuit an ”_alternating eto happen in the plate circuit? When there is no e rid potential (possibilities) is zero, there is a definite current in the plate circuit That current we can find fro 23 for it is where the curve crosses Zero Volts As the grid becorid is ative the current falls below this value The current, _I_{B}_, then is reater and less than the current when _E_{C}_ is zero

Youwhat happens when an alternating eto be fundamental to our study of radio

[Footnote 3: A mil-ampere is a thousandth of an ampere just as a millimeter is a thousandth of a meter]

LETTER 10

CONDENSERS AND COILS

DEAR SON: