The basic technical information contained in the Power Pentode lists is presented in several formats. Each giving a different angle to approach the search and utilization possibilities for substitute power amplifier tubes employed in vintage amateur radio transmitters and transceivers.
The abbreviations used to identify the data columns are indicated below along with an explanation of the importance placed on each.
TUBE:
The tube type shown is a numerical-alphabetical discription code. No absolute standard or convention was ever adopted to permit easy recognition of the purpose and application of electron tubes. In the case of ordinary TV and radio tubes, such as with 6BG6 or 12AU6, the 1st digit or digits indicates the significant portion of the required filament voltage. Some very loosely agreed upon guidelines were followed by some manufacturers for selection of the letters section of the code; but, not worth mentioning. Generally, the final digit or digits of the code represent the number of active elements or electrodes inside. Numerical coded tubes are usually designated as ruggedized or special purpose types.
BASE:
This information relates to the map of element connections to pins at the base of the tube and the location of the plate connection, either top cap or pin.
Again, not all manufacturers followed the same rules for matching base diagrams to the supposedly same tube built by someone else. An example of this appears
when examining the base configuration of the 6LB6 horizontal deflection
tube from RCA, Sylvania and GE. They are each different; yet, will work in
any application that calls for the 6LB6 with one possible exception. The GE does not
have the screen grid connected to pin #11, only to pin #3. The other two
have connections to both pins #11 and #3. And, there is even a minor variation
in the base of the RCA and Sylvania that results in those two having different
base maps. During the last few years of electron tube building in the USA, nearly
all manufacturers bought and sold tubes among themselves, putting the buyers
label on the tube. For example, Westinghouse sold receiving tubes for 12
years after they stopped making them. This was not because they had a large
enough inventory to last 12 years; but, bought from the dwindling group of
US and off-shore builders and closed down when the suppliers closed down.
Those familiar with each manufacturers characteristic features, which are
readily observed through the glass envelope, can identify the production
line origin. Only 8, 9 and 12 pin tubes are included in our listings in order to accommodate existing transmitter tube sockets, power supply considerations and, if necessary, the
general ease of only requiring minor wiring changes.
PLTD:
Means plate dissipation. This is the maximum amount of heat in watts that
a particular tube plate element can tolerate safely. Plate current under
normal operation will heat the plate. Excessive plate current, if not
checked by forced air or water cooling, will destroy or drastically reduce
the tenure of PA tubes. In pentodes, the higher the plate dissipation
rating, the longer the life expectancy, or in many cases, higher output power can be achieved over a tube with lesser plate dissipation capability.
MPLTV:
Maximum plate voltage. Most of the values listed are straight from the
manufacturers lips. Keep in mind that horizontal and vertical deflection
tubes were designed specifically for TV operation. The use of these tubes
for RF power amplifiers in HF transmitting equipment came later. The horizontal
output tubes (called sweep tubes in some circles because they "sweep" the
horizontal trace line across the screen.) never see, for example, the
rated 990 volts DC in TV service. But, under testing, were found to handle
that voltage level easily without coming apart. This fact really caught
the eye of amateur transmitter manufacturers.
AVEI:
Refers to average cathode current in milliamperes. One must be careful
how these ratings are interpreted. Remembering again, horizontal and vertical
deflection tubes operate at much reduced plate voltages than our amateur radio transmitting
equipment; therefore, the "average" cathode current is higher than what could
possibly be an "average" for the kind RF power amplifier duty we have planned.
Although, not having a perfect correlation,
this "average" current rating just happens to be
close to the highest peak currents that can be reached in transmitters before flat-topping occurs. This means a pair of
6LV6's, each rated at 400ma "average" cathode current can peak around
800ma under SSB modulation. Swan radio cathode meters can not
follow those peaks due to damping; thus, peaks of roughly 275ma
or so on the meter would equate to about 700 watts PEP input.
FVOL:
Filament voltage, normally AC or DC acceptable. In nearly all cases we show the numerical-alphabetic coded TV and radio tubes as being 6.3 volt types; however, tubes with other than 6.3 volt filaments were produced. Regardless of the required voltage, all tubes that have identical letter codes and final digits have exactly the same electrical characteristics. For example, a 6JB6 is identical to a 12JB6 electronically, except one is a 6.3 volt filament tube and the other is a 12.6 volt filament tube. Another example would be the 6LZ6 and 31LZ6 horizontal deflection amplifier tubes. One is a 6.3 volt filament tube, while the other is a 31 volt filament tube. The wattage
consumed by filaments is calculated exactly like that of a light
bulb. A 6JB6 filament would be heating at the rate of (6.3V X 1.2A) 7.56 watts.
FAMP:
Filament Amperes. A measure of the thundering electron flow through the filament.
SCRV:
Indicates maximum allowable screen voltage. Screen voltage has a major influence on how much current passes through the plate circuit.
SCRD:
Screen grid dissipation in watts. As screen grid voltage goes up, so does
the speed and abundance of electrons shooting towards the plate. That,s the job of the screen, to draw current from the cathode by overcoming control grid bias and then accelerate and direct that current toward the plate. However, in doing so, the screen starts looking like a smaller version of the plate and begins drawing its own current from the passing stream of electrons. So,
where there is current flow, there is heat and the screen
has a limit to the amount of heat it can fend off without melting. Screen grids will glow red similar to the "cherry red"
glow of the visible plate. However, being tucked inside and
enclosed by the plate, it can't easily be seen.
PWRO:
Typical power output. These figures are somewhat flexible; but, very reasonable capabilities. The old saying "All tubes are not
created equal." can certainly be applied here. Under test, electron tube performance varies among manufacturers and even over time within a manufacturers own product line. Prior to 1980, most people in the business knew which tube handled a particular task better than an other. The power pentodes we have listed, come from the various ranks of horizontal and vertical
deflection tubes, from predominantly audio amplifier backgrounds
and early on accepted RF power amplifiers. All will produce RF power. And many, particularly in SSB service, are capable of output power well in excess of the figures shown.
PLTC:
Plate circuit connection: Plate Cap or Plate Pin.
Courtesy K4BOV
