The Radio Boys at Mountain Pass Part 13

"We're more interested in receiving sets just at present," said Joe.

"Let's take a look at that end of the outfit."

"Anything you like," said Thompson, readily. "That panel is located on this side of the room."

"I suppose you use a regenerative circuit, don't you?" asked Bob.

"Oh, yes," answered the other. "That helps out a lot in increasing the strength of the incoming sounds."

"I suppose you use a tickler coil in the plate circuit, don't you?"

ventured Joe.

"No, in this set we use a variometer in the plate circuit instead,"

said Thompson.

"Speaking of regenerative circuits, have you heard about Armstrong's new invention?" asked Bob.

The operator shook his head. "Can't say that I have," he said. "It must be something very recent, isn't it?"

"Yes, I believe it is," said Bob. "I read about it the other day in one of the latest radio magazines."

"Do you remember how it worked?" asked Thompson, eagerly. "I wish you'd tell me about it, if you do."

"I'll do my best," promised Bob. "The main idea seems to be to make one tube do as much as three tubes did before. Armstrong found that the limit of amplification had been reached when the negative charge in the tube approaches the positive charge. By experimenting he found that it was possible to increase the negative charge temporarily, for something like one twenty-thousandth of a second, I think it was. This is far above the positive for that tiny fraction of a second, and yet the average negative charge is lower. It is this increase that makes the enormous amplification possible, and lets the operator discard two vacuum tubes."

"Sounds good," said Thompson. "Do you suppose you could draw me a rough sketch of the circuit?"

"Let's have a pencil and some paper, and I'll make a try at it," said Bob. "I doped it out at the time, but likely I've forgotten it since then."

Nevertheless, with the friendly aid of the eraser on the end of the pencil, he sketched a circuit that the experienced professional had no difficulty in understanding.

"You see," explained Bob, "with this hook up you use the regular Armstrong regenerative circuit, with the second tube connected so that it acts as an automatic switch, cutting in or out a few turns of the secondary coil. The plate circuit of the second tube is connected to the plate of the detector tube through both capacity and inductance."

"I get you," nodded the operator. "According to your sketch the plate and grid of the second tube are coupled inductively, causing variation in the positive resistance of the tuned circuit."

"That's the idea exactly," agreed Bob. "You see, this is done by means of the oscillating tube, the grid circuit being connected through the tuned circuit of the amplifying tube."

"Say, that looks pretty good to me!" exclaimed Thompson. "I wonder how Armstrong ever came to dope that out. I've been trying to get something of the kind for a long time, but I never seemed to get quite the right combination."

"Well, better luck next time," said Bob, sympathetically. "There are a lot of people working at radio problems, and it seems to be a pretty close race between the inventors. Something new is being discovered almost every day."

"If you fellows are building sets, you're just as likely to make some important discovery as anybody else," said Thompson. "That super-regenerative circuit is a corker, though. I'm going to keep that sketch you made, if you don't mind, and see if I can make a small set along those lines. I have lots of spare time just at present."

"It will repay you for your trouble, all right," remarked Joe. "We're figuring on doing the same thing when we get back home."

Jimmy had tried faithfully to follow the technicalities of the recent conversation, but his was an easy-going nature, disinclined to delve deeply into the intricate mysteries of science. Herbert was somewhat the same way, and they two wandered about the station, laughing and joking, while Bob and Joe and the young wireless man argued the merits of different equipments and hook-ups.

"Say!" exclaimed Jimmy, at length, "I hate to break up the party, but don't you think it's about time that we thought of getting back to the hotel? Remember we've got a long way to go, and it's four-thirty already."

"Gee!" said Bob, glancing in surprise at his watch. "I guess Jimmy is right for once in his life. We'll have to hustle along now, but we'll drop in here often while we are at Mountain Pa.s.s--unless you put up a 'no admittance' sign."

"No danger of that," laughed the other. "The oftener you come, the better I'll like it. This is a lonely place, as you can see for yourselves."

The radio boys shook hands with Bert Thompson, and after thanking him for the trouble he had taken to show them the station, they started back for the hotel at a brisk pace.

The days were growing very short, and it was after dark when they reached the hotel. Very warm and comfortable it looked as they approached it, windows lighted and throwing cheerful beams over the white snow outside. A red glow filled the windows of the living room, and the boys knew that a big wood fire was roaring and crackling in the big fireplace. As they drew close, a tempting aroma of cookery reached them, and caused them to hasten their steps.

They had barely time to get freshened up before the dinner bell rang, and in a short time they were making havoc with as fine a meal as any of them ever tasted.

When they told about their visit to the radio station, Edna and Ruth Salper, the daughters of the Wall Street broker they had met in the snowstorm, were among the most interested of the listeners.

"We find it so dull over at our house we are glad to come over here for meals and to visit," said Ruth Salper.

"I suppose being in the woods in winter is rather dull," returned Joe, politely.

"Did you boys really know enough about radio to talk all afternoon with the man in charge of the government station?" inquired Edna, curiously.

"Why not?" asked Bob. "Don't you think radio is a broad enough subject to talk about for an entire afternoon?"

"Oh, I suppose it is," she admitted. "But why don't you share some of your fun with us?"

CHAPTER XIII

PRESSED INTO SERVICE

"Just what do you mean?" asked Bob. "Do you want to talk radio with us all tomorrow afternoon?" he went on, with an irritating grin.

"No, of course I don't, stupid," she exclaimed. "But why can't you bring your old wireless things into the hotel parlor and let us all hear some music? We'd be ever so grateful if you would."

The radio boys looked doubtfully at each other.

"We'd do it, fast enough," said Bob. "But we didn't bring a loud speaker with us, and without that n.o.body could hear much unless he had a set of telephone receivers."

"Oh, dear!" she exclaimed. "I just knew you'd make some excuse or other."

"A loud speaker is something that looks like an old-fas.h.i.+oned phonograph horn, isn't it?" asked Ruth, the younger sister, before any of the radio boys could refute the older girl's accusation.

"Well, yes, it looks like that; but the details are different,"

replied Bob.

"Yes, but if you had a phonograph horn, couldn't you fix it up so that the music would be loud enough for us all to hear it?" persisted Ruth.

"Good for you, Ruth!" exclaimed her sister. "I know what you mean.

You're thinking of that old phonograph they used to have in this hotel, before they got the big new cabinet machine."

"If Edna and I get that horn for you, it will be easy for such experts as you boys are to make a--a what-you-may-call-it--loud speaker--out of it, won't it?" asked Ruth, demurely.