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VACUUM TUBES VS. SOLID STATE
By Ross Goodall, WD4NJV

Both tubes and solid-state parts are used today.  

In Amateur Radio, we want the cleanest signal with minimum drift and distortion.  Size and power consumption matters.  Before the introduction of phase-locked loop (PLL) technology, receivers and transmitters drifted in frequency. 

Back then, tubes had to warm up.  Capacitors and resistors changed values causing frequency drift. Some old Hammarlund tube receivers offered an optional 24-hour clock with a timer that served two purposes: one, to tell you the 24-hour time and two, to turn on the equipment approximately 20 minutes earlier than your desired operation time to allow the equipment to reach frequency stability.

Each tube type has different uses and operating characteristics.  See tube manuals for details.   1,2

Examples: The OB2 is a mercury vapor tube which glows purple, 12AX7's will light up momentarily bright white, a 6L6 comes both in a taller version and a shorter/wider version, an important consideration for tight spaces. 

The 6E5, 6G5, 6H5, and 6U5 are known as electron-ray indicator tubes or tuning/magic eyes and were used for setting volume levels and receiver tuning. 6BM8s were known to be microphonic in some applications and needed convection cooling.

AM broadcast band radio receivers commonly used a tube lineup of 50C5, 35C5, 12AT7, 6BE6, 12SK7, 35L6, 35Z5, 12SA7, 12BA6, 12BE6, 35W4.  Many would run on either AC or DC current. Tubes were selected so filament voltages would total 110-120 volts eliminating the need for a line transformer.

Earlier radios had larger tubes and commonly used 41, 6A7, 78, 76, and 80 tubes.

Years ago, it was fun and easy to keep tube equipment operating by pulling the tubes and taking them to the tube tester at local stores.  Although these testers could screen for weak tubes, most did not test them under a load.

6146, 807, 811A, 813A, 3-500Z are among tubes which have long been widely used in amateur equipment.   3

MODERN TUBES

Inductive output tubes (IOT tubes) are used today in high power television broadcast transmitters and are water cooled with an antifreeze solution. 

As far as which is best for guitar and other music amplifiers, it is a judgement call based on what is pleasing to a musician’s or audiophile's ear. Distortion is desirable to make unique sounds. 

Jimi Hendrix's music is an example of including intentional distortion. For small musician groups, you may see an amplifier sitting on the stage.  Popular brands are Fender and Marshall amps. 

Today for big, well-known performers, you will probably note the guitars and other instruments connected without wires to computer sound processers being overseen by multiple sound technicians behind stage.

Tubes to many people, are a beauty to watch as they heat up, glow, and to hear the warmth of their sound. Tube amplifiers such as McIntosh are considered to be the top of the line.

Today most tubes made are foreign made due to labor costs.

VACUUM TUBE AND SOLID STATE TECHNOLOGY COMPARED

Tube Advantages:

Better sound quality

Smooth clipping widely considered more musical

Tolerant of large overloads and voltage spikes

More accepting of operating in high temperature environments

Wider dynamic range due to higher operating voltages and overload tolerance

Output transformer protects speaker from DC voltages due to malfunction and protects tubes from shorts

Easy user replacement

Older tubes are available for decades

Tube Disadvantages:

Bulky, less suitable for portable products

Higher voltage and power consumption

Heater supply creates waste heat, tubes break, some tubes have microphonics problems

Solid state advantages:
Lower cost

Can be combined to make an integrated circuit

Lower power consumption

Less heat

Operates using lower voltage power supplies for greater safety

Lower costs

Allows tighter space clearances

Improved physical ruggedness

Solid state disadvantages:

Sharp clipping considered to be not-musical

Device parameters may vary widely with temperature with thermal runaway possible.

May require large heat sinks for power transistors

Less tolerant of overloads

Greater tendency to pick up RF

More difficult to replace by user

Older transistors and ICs may become unavailable after 20 years or so.  4
 
References:
1.      RCA Tube Manual

2       ARRL Handbooks earlier editions

3       RF Parts Company

4       Effectrode: Vacuum Tubes and Transistors compared

  EIMAC TUBES

By Ross Goodall, WD4NJV

All Eimac tubes are made in the United States by Communications and Power Industries (CPI) and have been made in America since the company was founded in 1934.

Eimac tubes are used in many amateur radio applications as well as in broadcast television and radio transmitters.

Reliability is of utmost importance in broadcast applications. If a transmitter goes offline, advertising revenue is lost as well as listeners & viewers.  News, weather and safety messages cannot be broadcast. 

Broadcast engineers realize the importance of keeping their transmitters on line and their job depends on it. 

Eimac replacement tubes are readily available and are advertised in QST magazine.  Eimac’s first ad was in the November 1934 QST issue.

In 1932, two radio amateurs Jack McCullough, W6CHE and Bill Eitel, W6UF decided to build high-power transmitters to work some of the 20-meter stations being heard in California. They wanted to develop a tube that would operate at lower voltages than the existing 204 and 852 tubes.  Their tube was the 150 T triode.

Their company later expanded to create many other tubes.  In 1935, tubes were sold to the U.S. Naval Research Lab for use in an experimental radar that operated on 200 MHz.  The tube used was the 150 T because it was able to produce high pulsed power at high plate voltage. 

By 1938, U.S. airway routes were developing as well as HF aeronautical radio links.  Eimac's 450 TH was used in broadcast radio, including new Armstrong FM broadcasts and experimental television. 

Eimac's popularity grew with amateurs worldwide as its products dependability became well known.  Eitel and FM inventor Armstrong met regularly to discuss problems and fixes.

In 1940, Eimac received an order from Western Electric for 10,000 tubes.  After World War II concluded, Eimac evolved creating new tube types including 4X150A beam tetrodes, television klystrons and microwave tubes. 

In the late 1980’s, Eimac developed a newer inductive output tube from klystron and tetrode technology.   1   IOTs are a very important part of broadcast transmitters today.  IOTs are expensive and must be handled carefully.

Today Eimac produces tubes for broadcast, communications, radar, industrial heating, semiconductor processing, medical (MRI and PET). Their webpage contains valuable information about linear amplification SSB, tube performance, extending tube life and shipping and handling power grid tubes. 2

As Bill McCullough and Jack Eitel said, “if it were not for amateur radio, Eimac could have never existed”.  1

A great trip is to visit to a high-power radio or television broadcast station with a guided tour by an engineer and have them point out each section of the transmitter and its function.

Today, most broadcast transmitter sites are unattended and secure, so contact should be made directly through the station’s general office to the chief engineer. There are many YouTube broadcast transmitter videos available.

A big thank you goes to Linda DiLorenzo, KI6JF, for help and authorization to use Eimac’s information in creation of this article.

References:
1 Ethw.org, Eimac Vacuum Tube Manufacturing (used by permission granted May 9, 2018 by Linda DiLorenzo KI6JF)

2 CPII. com, CPI communications and power Industries