PL3-500ZG
Power Triode
The Penta Laboratories PL3-500ZG is a high-mu power triode with a maximum plate dissipation rating of 500
watts. Cooling is by radiation and forced air through the base, along the envelope, and over the plate seal
and radiator-type plate connector. It is intended for use as a zero-bias Class AB2 amplifi er in radio-frequency
or audio frequency applications. By eliminating the bias supply , zero grid bias operation greatly simplifi es cir-
cuitry design. When operated in a cathode-driven circuit, a power gain of as much twenty times is achievable.
Electrical Characteristics
Filament
Voltage ..................................................................................5.0 Volts
Current (Ef=5.0 V) .................................................................14.6 Amperes
Average Amplifi cation Factor ......................................................130
Direct Interelectrode Capacitances - Grounded Grid
Input ......................................................................................8.3 pF
Output ...................................................................................4.7 pF
Feedback ..............................................................................0.07 pF
Maximum Frequency for Ratings................................................110 MHz
Mechanical Characteristics
Base ...........................................................................................5 Pin Special
Net Weight ..................................................................................7.0 Ounces
Maximum Overall Dimensions
Length ...................................................................................6.10 Inches
Diameter ...............................................................................3.44 Inches
Mounting Position .......................................................................Vertical, base up or down
Cooling .......................................................................................Radiation and forced-air
Recommended Socket ...............................................................PSK410
Revised 11 July 2013
P E N T A L A B O R A T O R I E S
9740 COZYCROFT AVENUE * CHATSWORTH * CALIFORNIA 91311
(800) 421-4219 * (818) 882-3872 * FAX: (818) 882-3968
ELECTRON TUBES FOR INDUSTRY
PL3-500ZG Power Triode
Application Notes
Cooling
Forced air cooling of the base, base seals, envelope, plate seal, and plate connector is required for all
classes of operation when the PL3-500ZG is operated at or near the maximum plate dissipation rating. A
total of 14 c.f.m. of cooling air, properly distributed to the base, envelope, and plate seal area is required.
Such cooling is most conveniently provided by means of a pressurized chassis upon which the standard
tube socket is mounted in a special cut-out. The use of a glass chimney is advised.
Air at the proper pressure and quantity may be obtained from a small centrifugal blower rated at about
100 c.f.m. of free air. Cooling is adequate when the base seal temperatures do net exceed 200° C and the
plate seal temperature does not exceed 225° C. At lower dissipation ratings, it may be possible to operate
the PL3-500ZG with less extensive cooling apparatus; however, in all cases, air fl ow rates in excess of
the minimum requirements will tend to prolong the tube's useful life.
Mounting
It is mandatory that the PL3-500ZG be operated in a vertical position, with the base either up or down.
Severe shock or vibration will result in damage to the tube, and should be avoided.
Zero-Bias Operation
At plate voltages exceeding 2500 volts, operation at zero bias is not recommended as maximum plate
dissipation max be exceeded. A zener diode placing positive bias on the cathode or other fi xed voltage
source may be used to reduce the zero signal plate current at potentials exceeding 2500 volts.
Class C Operation
Although designed for linear amplifi er use, the PL3-500ZG may be operated as a class C power amplifi er
or oscillator or as a plate modulated RF power amplifi er . When operating at plate voltages of below 3000
volts, the zero bias characteristics of the tube can be advantageous.
Input Circuitry
In order to maintain the highest degree of linearity and greatest power output when the PL3-500ZG is
used as a grounded grid RF amplifi er, the use of a resonant tank in the cathode circuit is advised. With
a single ended amplifi er, for best results it is recommended that the cathode tank circuit operate at a Q
of fi ve or greater.
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PL3-500ZG Power Triode
Typical Operation - Cathode Driven RF Linear Amplifi er
Plate Voltage ..............................................................................2500 3500 Vdc
Cathode Voltage .........................................................................0 +15 Vdc
Zero Signal Plate Current ...........................................................130 53 mAdc
Single-Tone Plate Current (CW) .................................................400 400 mAdc
Two-Tone Plate Current ..............................................................280 262 mAdc
Single-Tone Grid Current ............................................................120 108 mAdc
Two-Tone Grid Current ...............................................................70 58 mAdc
Single-Tone Power Input ............................................................1000 1400 Watts
Useful Output Power (CW or PEP).............................................600 890 Watts
Resonant Load Impedance ........................................................3450 5000 Ohms
Intermodulation Distortion Products
Third Order ...........................................................................-33 -40 dB
Fifth Order ............................................................................--- -45 dB
Driving Impedance......................................................................100 115 Ohms
Maximum Signal Driving Power..................................................46 46 Watts
Maximum Ratings
DC Plate Voltage ........................................................................4000 Volts
DC Plate Current ........................................................................0.4 Amperes
Plate Dissipation .........................................................................500 Watts
Grid Dissipation ..........................................................................20 Watts
Typical Operation - RF Power Amplifi er or Oscillator - Grid Driven
Plate Voltage ..............................................................................3000 3500 Vdc
Grid Voltage ................................................................................-10 -75 Vdc
Plate Current ..............................................................................350 300 mAdc
Grid Current ................................................................................115 115 mAdc
Peak RF Grid Voltage .................................................................110 187 Volts
Approximate Driving Power ........................................................14 22 Watts
Plate Input Power .......................................................................1050 1050 Watts
Plate Dissipation .........................................................................330 200 Watts
Useful Output Power ..................................................................720 850 Watts
Resonant Load Impedance ........................................................4200 5700 Ohms
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