RF Parts Company  

Tube Applications & Suggestions
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For fewer problems, we recommend using matched tubes in equipment. Transceivers neutralize better using matched tubes. Tube life is improved significantly due to better power sharing and fewer parasitics. We test all sweep and special purpose tubes. The best tubes are selected into matched sets. Tubes which do not fall within optimum parameters are sold as "singles" (which will work as drivers). "Out of Spec" or marginal tubes are discarded.

TV Sweep Tubes have not been manufactured for some time. The best tubes were made before 1983. RCA, Sylvania, ECG, and certain production runs of GE, Raytheon, etc., seem to be much better made than tubes built after 1983. Tubes available for sale in the last few years do not seem to hold up as well as original tubes that came in the equipment. From about 1950-1980, SSB amateur radio equipment often used sweep tubes in "SSB" amplifiers. Amplifying "AM" signals can overheat tubes due to their low power dissipation. When using sweep tubes, care should be taken to limit carrier level to about 50 watts output per tube (6LQ6, 6LF6, 6JE6, 6HF5, 6JS6C, etc.). SSB P.E.P. can operate at about 70 watts P.E.P. per tube. Exceeding these power levels will rapidly reduce tube life. Don't be confused by the model number or claims of some equipment such as D&A, Varmint, etc. They are overly optimistic.

Addition of the "modulator" type of AM drivers can damage tubes due to the high peak and average drive power. You should approach high peak power with care.

Palomar Skipper 300, 300A, 321: use tall GE tubes with required modification to cabinet. (Short GE 6LF6 & 6KD6 are not available.) Some ECG 6LF6 or 6KD6 are available in short size. Palomar 350Z: GE 6LF6 or 6KD6. Dentron GLA: 6JE6/6LQ6 at 70% power.

Kenwood/Heathkit/Yaesu/Etc: use only matched 6146B or 6146W. (Our Sylvania 6146W is a ruggedized premium grade 6146B which pass military quality specifications.) US manufactured 6JS6C in Yaesu requires simple neutral modification. This tube is in extremely short supply.

Swan Transceivers require special tube selection for ease of neutralization. You may call our Technical Department at (760) 744-0750 for details.

Our tests have shown that Graphite plate 3-500Z tubes safely handle about 10-20% higher power levels over metal plate tubes. Graphite tubes will not "burn through" or melt at temperatures which destroy regular metal plate tubes. Additional air flow may be required in AM or RTTY. Remember, you must have sufficient cooling.

Transmitting tubes generally require a "burn in" time to increase emission to its nominal value. In broadcast stations, 1-3 hours at rated filament voltage is allowed for burn in. This initial operation allows the getters, materials which absorb and hold residual gas, to finish the vacuum of the tube in its final operating environment. In an Amateur Radio amplifier, tubes will sometimes require 50-200 hours of accumulated "key down" transmit time to remove the residual gas and condition the filament for full emission. It is well advised to allow tubes to operate in standby mode (filaments on, no transmit) for 30 minutes before tune-up.

The 811A, 572B, 3-500Z, 4-400, etc. utilize a thoriated tungsten filament, which is highly dependent upon sufficient filament temperature to provide adequate electron emission for normal operation. Emission increases as the thorium migrates towards the surface of the filament wire. This is why it is recommended to "burn in" these tubes before operation. Some amplifiers exhibit higher than rated filament & plate voltages due to excessive AC line voltage. This is often the case with older equipment rated for 115 or 230 VAC operated on our standard (higher) line voltages i.e. 120/240 VAC.  Should you find the filament voltage is greater than the tube is spec'd for, adding a small amount of resistance in the primary of the filament transformer can reduce it to proper value.  If the filament power comes from a multi-winding transformer (where additional windings are in addition to the filament winding), adding a small resistance between the filament winding and the tube socket will work. 

Note: excessive filament voltage above that specified for the tube will result in significantly shorter filament life.


When Chinese tubes were first imported to the U.S. (early 1990's), we found quality inconsistent and varied from factory to factory. These early 811A, 572B, and 3-500Z tubes also suffered from filament weakness. RF PARTS has worked closely with what we have found to be the best tube factories to improve product quality.

Today, our 3-500ZG tubes offer excellent reliability. From 1993—2009, RF Parts branded 3-500ZG tubes returned under warranty were less than 1% of total sold. This figure ranks up with the best of U.S. and European tubes, and allows RF PARTS to offer a TWO YEAR Transmitting Tube Limited Warranty against defects in material and workmanship on our RFP brand 3-500ZG. It is the BEST in the industry!


Use of excessive filament voltage to control tube output, i.e. to increase emission for more output, will destroy a tube's filament. In the most of applications, end of life is where tube emission is no longer adequate to sustain full output power or allowable distortion levels due to decarburization of the filament. (Carburization is the process where in manufacturing, carbon is, under specific conditions of temperature and pressure, burned into the raw thoriated tungsten filament.) As the tube operates, carbon is slowly burned out of the filament.

Another factor affecting tube life is the residual vacuum level which affects the rate of decarburization, primarily oxygen and nitrogen reacting with the filament. This is where quality of manufacturing becomes important in aging tubes.


The familiar tube manufacturers Sylvania, General Electric, Raytheon, RCA, ECG, etc., have all ceased production in the early 1980's. The tubes being offered now are either existing shelf stock or foreign imports. We have found it necessary to fully test most audio and sweep tubes to weed out the weak and defective ones. For that reason, we may charge a bit more for our efforts.

As with semiconductors, manufacturers of sweep tubes do not warrant their tubes after installation, as there is no way of knowing if there are problems in the equipment, method of operation, etc. If your equipment uses sweep tubes, it is best to reduce power and drive level to lengthen tube life.

Price and availability subject to change without notice.

This page last updated: 11 November, 2010

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