Part 13 (1/2)

”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.”