Thursday, June 6, 2013

The "Little Howler"

It wasn't long after the early adventures with my first crystal set that my adventures in electronics took a quantum leap. Our family had moved to the small West Texas town of Coleman for a job my dad had in construction. While I was there, I had begun reading everything in sight that had to do with radio. The favored publication was The Radio-Tv Experimenter, not only for the construction projects but also because it included in the back portions of White's Radio Log that had lists of radio stations.

I had already begun dismantling old radios and organizing parts, all in hopes of having the parts to build one of the projects, But there never seemed to be more than about half of the right values of capacitors and resistors and none of the tube types or power supply materials. My folks were not to pleased about the idea of a nine year old working with high voltages either.

As luck would have it, I had been sending off for all kinds of free stuff from the coupons in the radio magazines I was reading, and one of the freebies was the then famous Allied Radio catalog, with over three hundred pagers of things to drool over and want. I didn't know it at the time, but my dad was also paging through it and Santa Claus that year brought me the Knight-kit Twelve-in-One kit: a breadboard outfit with which you could build twelve different projects, all centered around one tube and run by a twelve volt power supply. No high voltage ( the single tube was a 12K5 designed for use in car radios with only 12 volts on the plate).

The first part of the project had to do with mounting all of the parts and assembling the power supply, which was then enclosed in a metal cover. The 12K5, power transformer, rectifiers and power supply filter capacitors were all under the cane metal cover. Then all of the other individual parts that would be used in any project were mounted between solder lugs on long terminal strips, with each project wired by placing jumpers among the various lugs on the terminal strips.

The decision on which project to build first was easy. It would be the radio receiver as I wanted to see if it would pick up more than the crystal set I had used at our old home. I did not have an antenna up at the new rented house for it and it was sitting unused.

Running all the jumpers for the project took a couple of evenings. My soldering technique was not fully developed and things went a little slow. My dad checked my connections and had me do several of them over. I did not have a soldering gun in those days and was using his old soldering iron.

Finally came the time for the trial. This was the first of many such moments, when the little pause takes place. There is a moment when one mentally reviews everything that has been done and thinks a moment about the consequences. There is that short pause where the finger won't quite push the button, turn the switch, or in this case plug in the a.c. Cord because there was no power switch.

I did not know it at the time, but this would be the first of many such pauses in my life when powering up a new device or bringing one back up that had been repaired. That would range from small projects to audio mixing consoles in radio stations to 30-kilowatt transmitters. It is a moment of truth when the verdict will come in on what has been done, either in the form of proper operation or a puff of smoke, of a clank of relays and the proper hum of transformers and the roar of blowers or the “bang, slam” of contactors slapping back off or the shotgun sound of a huge arc and then the “slam bang”. With some of the big transmitters in years to come there would be the strong urge to get a long stick to push the “plate start” switch from another room, as if all of the potential power would leap out of the button and strike me down in retribution for some mistake made!

In this case there was no sound at all when the a.c. cord was plugged in. There was no click or a relay, no pop in the headphones, not even a hum from the transformer. The only indication that something was happening was the light of the tube that gradually faded up and shining through the vent holes in the metal cover over the power supply. But I hardly noticed because I was looking everywhere for tell tale smoke that would have signaled some fatal wiring error.

The next step was to attach an antenna to what now appeared to officially be a receiver. Only a short piece of wire was supplied with the kit for I recall less than 20 feet of very kinky stuff...It was strung out the kitchen door under the overhang of the house.

Then it was time to put on the headphones. I was not sure what, if anything, I would hear. The local radio station in Coleman, Texas was a 250 watt daytimer and it being after dark, would not be there for the big test. From my experience with the crystal set I was not expecting much out of a single tube, simple radio. I put the familiar old Bell headphones on.

The kit instructions said to turn the regeneration control ( the only potentiometer on the little circuit board) until I heard a “plop” in the headphones. Plop? I rotated the pot back and forth several times, not sure whether I had heard the plop or not, just a bit of a hiss. I left it about three quarters open and read the next step: “Tune the tuning capacitor until you hear a whistle or a station.”

OK, that was understandable. The tuning capacitor on this kit was not a regular “plate meshing” type, but a compression mica type mounted on an L-bracket. To go from minimum to maximum capacitance, you rotated the shaft many, many times as a screw going in and out moved the plates further apart or closer together with mica sheets in between the plates.

My left hand as shaking a bit as I reached out and began rotating the tuning knob. There were a few faint whistles, but as I continued to turn, I came across a louder one with what sounded like voice mixed under it. I looked back at the instructions and saw that it said to turn the regeneration control counterclockwise until the whistle stopped and voice or music could be heard.

That was done, and the station was audible! And the good news, for me at least, is that the volume was much louder than what I was used to hearing from the crystal set. I listened for the station ID, though the announcer voice sounded somewhat familiar. It was KRLD in Dallas, over 150 miles away! And this was without the big antenna I had for the crystal set at my old home! This was a new era!

Tuning a regenerative receiver is an art. It requires a soft touch, slow, deliberate movement and and patience. It requires a feeling for how the detector is reacting to the difference in signal strength, how close and how strong the adjacent signal is. With the little receiver, it was a matter of running the regeneration control up until the detector was in oscillation with each station appearing as a whistle.

Then when the whistle was centered with the tuning control to an almost zero-beat, it was a matter of backing off the regeneration until the whistle just stopped and hearing the audio of the AM signal. There being no additional audio amplification, the audio was sometimes a bit low and if the signal was too weak, it would not be audible. It was still better than the crystal set, and the selectivity was much better, too. The sensitivity and selectivity was the best when the regeneration was set as close as possible to the oscillation point without going into howling. That's where the “art” in tuning the set came in!

Unfortunately I was not keeping a detailed log at the time this project was completed, so I am not certain what all I was able to hear with it, other than trusting memory. It seems the major clear channel ( little letter, not the company!) stations were logged along with a number of Mexican stations that I could not identify at the time.

A few years later, this same receiver was used for DX-ing during a stay with my grandmother one weekend with wire strung around her kitchen. By then, the skills of tuning a regenerative receiver had been honed to an edge. Also identifying the stations was made easier because I had become familiar with the broadcast band and was able to identify and log stations on almost every clear channel and many of the regional frequencies in one night's listening. I do have records of that night's tuning and they are documentation on just what can be done with a very simple receiver. In fact, except for volume and only being able to drive a headphone, just about everything was logged that could be heard on my then main receiver, a Watterson All American Five with longwire antenna at home.

It is too bad that I had not been keeping a detailed log earlier.

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