-DECEMBER 2008-
-The Way We Were:
The Early Years of Electronics
-Sponsors: Antique
Electronic Supply, Calao Systems
-The Circuit
Cellar Reader: A Proven Doer
The Way We Were: The Early Years of Electronics
Reginald Neale
In 1953, when I started my career in
electronics, transistors were still laboratory-based curiosities. Vacuum tubes
were big business. In addition to the OEM demand created by radio and TV set
sales, there was a huge replacement market. Just like incandescent lamp filaments,
tube filaments eventually burn out. Slow chemical
changes and mechanical stresses from thermal cycling gradually degrade
performance or cause internal shorts. That’s why tubes are socketed
devices.
Photo 1
Today’s TV service industry is mostly limited
to swapping modules. It was a lot different at the height of the tube era, when
every village had a TV repair shop. The repairman made house calls, carrying a
big tube caddy with the most commonly needed tubes and tools, including a basic
tester like the one shown in Photo 1. When a tube was plugged into one of the
sockets, an intact filament caused the neon indicator in the center to go out.
The “interlock” power cord connector on the removable back of the TV set
supplied 115-V AC power for the tester. The occasional set that couldn’t be
repaired in the customer’s home would have to go back to the shop, where the
repairman would diagnose problems down to the component level.
Common radio/TV tubes had filament voltages
of 6.3 or 12.6 V, at 300 or 150 mA, respectively.
Almost 2 W per tube just to get enough electron emission from the cathode, and
you hadn’t done any useful work yet. Power tubes used even more. No wonder the
filaments were also called “heaters.”
You might think that since the glow of the filament
is usually visible through the tube’s glass envelope, a filament tester would
be unnecessary. Well, some tubes had metal jackets. In some radios and
televisions, tubes had hard-to-remove external metal shields. Some tubes had
opaque parts that made visual inspection difficult. But the biggest reason was
economics. To save money, many radio/TV manufacturers built sets without power
transformers. Tube filaments were wired in series across the AC power line.
Millions of sets were produced with this cost-cutting strategy. When one tube
burned out, they all went dark. You had to guess which one was really dead.
The next step up is an emission tester, which
tests the tube as a diode, with all the electrodes in the tube except the
cathode connected together. A “good” reading is a necessary but insufficient
test result. It tests the filament and the cathode emission, but it doesn’t
test for the ability to amplify. More expensive mutual conductance testers like
the one in Photo 2 feed the tube a signal and display BAD/FAIR/GOOD output
performance on an analog meter. A set of lever and switch settings for each
tube type are accessed from a long roll chart. The narrow window with the list
of settings is visible at the bottom. The most expensive testers measured
actual transconductance in millimhos, and also had
the capacity to check for high-resistance shorts between electrodes. Hickok and
Precision Apparatus Co. were the most respected names.
It’s interesting to think about how you might
update a general-purpose tube tester for 2009. In fact, there are specialized
tube testers available today for the audiophile market; but they only test a
small number of types used in high-end audio equipment, with prices to match. A
general-purpose tester would still need all the sockets, but you could use an
LCD to confirm your selection and to display the test result. You’d need enough
memory for a LUT with thousands of entries, and a way to update it easily. A
multilayer menu could get rid of most of the knobs and switches. Use some
programmable power supplies for the filament and electrode bias voltages. An
embedded controller could manage the application, while simultaneously
providing a variable signal source and synchronous detector. Add some discrete
semis to switch resistor networks for establishing electrode voltages. It seems
very doable, but the price, once adjusted for inflation, probably wouldn’t be
any better than the 1950s version. The size and weight might be decreased a
little. The main advantages might be improved flexibility and reliability.
Finally, vacuum tubes were the building
blocks of the first electronic digital computer, ENIAC. Figure 1 is the diagram
of a flip-flop, which could store one binary bit. It used a single twin-triode
tube, a handful of discrete components, and 2 or 3 W of power. In the 60-plus
years since then, there have been amazing exponential improvements in the size,
speed, and power requirements of computer hardware. T. J. Rodgers of Cypress
Semiconductor notes that if automotive technology had followed the same
trajectory, today you would able to buy a Chevy for a penny and it would get
10,000 miles per gallon.
There were also vacuum tube analog computers. That’s a whole
different story that’s better suited for another installment.
About the author:
Reginald Neale is well into his golden years, but prefers to take his
retirement in installments, a few months at a time. He has long been afflicted
with a reluctance to discard anything exotic, wonderful, curious, weird, or of
exceptional quality. You can share information about electronic engineering
history with him at reg_neale@yahoo.com
(use CC in subject line).
Antique Electronic Supply
Antique Electronic Supply is your source for vacuum tubes, carrying the largest
supply of new old stock and current production in the world. We carry it all
for vacuum tube equipment as well as Jensen speakers and parts for guitars,
organs and keyboards. Please visit our secure website at http://www.tubesandmore.com/.
CALAO Embedded Computer Board
USB-A9260-C02
Embedded Computer with USB form-factor (36 x 85 mm),
ATMEL AT91SAM9260 @ 180MHz,
256MB NAND Flash (8bits),
64MB SDRAM (32bits @ 90MHz),
Ethernet 10/100,
2 USB Host,
USB Device,
USB Debug (Serial DBGU + JTAG + Power Supply).
All our boards come with Linux pre-installed.
http://www.calao-systems.com
Think
You Have a Great EQ Challenge of Your Own?
E-mail your best EQ question and
answer to eq@circuitcellar.com. The best EQs will be published by
Circuit Cellar. Authors of the top four EQ picks will receive an Atmel In-Circuit
Emulator mk-II.* All published EQs will earn the author a Certificate of
Appreciation from Circuit Cellar.
Problem: One way to measure small time delays is to do it in terms of the phase shift of a sine wave signal. For example, if you modulate the beam with an 83-MHz sine wave, which has a wavelength of approximately 3.6 m, one degree of phase shift represents about 1 cm of distance.
However, measuring phase shifts accurately at high frequencies has its own set of problems. How can this be mitigated?
Solution: The phase shift measurement problem can be made easier by shifting the two signals down to a lower frequency by mixing them with a second signal whose frequency is extremely close to the original signal frequency. For example, if the signal frequency w1 is 83 MHz and the mixing frequency w2 is 82.9 MHz, the difference frequency is just 100 kHz.
How does this help, exactly? The transmitted signal is
The received signal, delayed by time Dt, is
The delay can also be expressed as a phase angle f, where f = w1Dt.
The transmit mixer output, after filtering, is
The receive mixer output, after filtering, is
Rearranging terms, you get the following:
In other words, the phase angle introduced by the time delay is preserved through the mixing process even though the output frequency of the mixers is several orders of magnitudes lower. This makes sense intuitively if you consider that if the two high-frequency signals slip past each other by one full cycle, the beat frequency outputs of the mixers must do the same thing.
The time delay Dt¢ represented by this phase angle has been multiplied by the ratio of the original signal frequency to the mixer output frequency, making it much easier to measure.
Additional information on this topic can be found at www.uow.edu.au/eng/phys/200labs/phys205/spdoflght.pdf.
*EQ award of Atmel In-Circuit Emulator mk-II: recipient responsible for any applicable duties and taxes. No cash alternative. Awards will be made at sole discretion of Circuit Cellar editorial staff. By submitting an EQ Q&A, Circuit Cellar is granted the right to publish the submitted material and the author’s name. Submissions must be original (not published in print or online previously). Offer valid through 3/31/09.
The Circuit Cellar
Reader: A Proven Doer
Sean Donnelly,
Publisher
There are several highpoints throughout the year that make me proud of Circuit Cellar’s audience. Of course, I feel this way with every edition of the print magazine we publish. When you consider that more than half of each issue comes from Circuit Cellar reader submissions, and you take into account the quality of those submissions, this sense of pride in the Circuit Cellar design community is well justified.
This is certainly true of the recent USB Starter Board evaluation program Circuit Cellar administered on behalf of Microchip Technology. I was most impressed with the detail, resourcefulness and insight presented by the vast majority of Circuit Cellar participants. Evaluators didn’t just try to make an LED blink to satisfy a basic duty and make off with a freebie starter kit. They opened up these sample products to every possible real-world challenge they could find. To top it off, participants went well beyond critiquing the samples; they provided innovative solutions. This is of particular value when a company is giving Circuit Cellar readers an exclusive first look at a Starter Kit that’s still in development. The Circuit Cellar impact on future product design has the potential of being quite extraordinary.
The variety of input was incredible. I saw evaluators reworking documentation and applying their own organizational wish lists they accumulated over the years. One resourceful designer even went as far as editing a tutorial movie to provide pacing and emphasis to meet his needs. As I pored over these evaluations, it became clear that participants were truly concerned about providing the best possible start-up experience for the larger design community. It’s a behind-the-scenes contribution that’s worthy of praise.
For a more public contribution, I encourage readers to consider an article submission to Circuit Cellar’s print magazine. Circuit Cellar has published application articles from an incredible range of designers—from expert authors to engineering students. The common denominator is the great engineering behind the project discussed in the article. Let our editorial team help you turn a great project into an amazing Circuit Cellar article. Your peers will thank you for your contribution. For a quick view of our editorial submission guide, visit http://www.circuitcellar.com/submissions/guidelines.html/.
Below you’ll find a few photos
from some of the exciting projects in Circuit Cellar’s upcoming January issue.
These include a project that proves a method for developing a software-defined
radio using a microcontroller; a virtual instrument interface for controlling
MIDI input and capturing audio output over the Internet; and a PIC-based
accurate frequency reference that is synchronized to a GPS clock.
