4X500A

[Keith Rowland]

J. Douglas Hensley, W5JV wrote:
>
> Does anyone have any articles, schematics, etc. using the 4X500A in an HF
> amp configuration?  This was a popular tube used commercially as a
> modulator.  I've access to some "pulls" but have found zip references
> using them.
>
> 73,  Doug
>
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Hi Doug:  After researching this tube since yesterday, I have found only
the specifications for it--no articles using it as an amateur amp.
However, you may be able to design something, using the specs as a
guide.  This response is being posted to the entire list in the event
that someone else may have some of these tubes and can use the info.

4X500A:  Beam Power Tetrode.  External cap is Plate connection.  A base
connection and the external ring are the G2 (screen grid) connections.
Pins one and 3 are the filament connections.  The remaining pin is G1
(control grid).

This is a forced-air-cooled type with integral plate radiator and
thoriated-tungsten filament.  It is used as an RF power amplifier and
oscillator.  It can be run at full input to 120-mHz.  The Class C
Telegraphy maximum CCS (Continuous Commercial Service) plate dissipation
is 500-watts.

The tube may be mounted only in the vertical position, either with the
base up or down.  Sufficient forced-air cooling must be provided to
limit the temperature of the metal-to-glass seals and the radiator core
to 150 degrees Centigrade.  Forced-air cooling must begin before
filament voltage is applied, and must continue until all voltages have
been removed from the tube.  A minimum air flow of 40 cubic feet per
minuteis required when the tube is operated at maximum CCS ratings.

                     OPERATING DATA

Filament Voltage (AC/DC)..........................5.0 volts
Filament Current..................................13.5 amperes
Transconductance with plate voltage of 2500, plate
current of 200 milliamperes, and grid #2 voltage
of 500.............................................5200 micromhos
Direct Interelectrode capacitances:
   Grid #1 to Plate:               .05 Pf
   Grid #1 to Filament & Grid #2:  12.8 Pf
   Plate to Filament & Grid #2:     5.6 Pf

      SPECS FOR OPERATION AS AN RF POWER AMPLIFIER AND OSCILLATOR FOR
      CLASS C TELEGRAPHY AND AS AN RF POWER AMPLIFIER FOR CLASS C FM
TELEPHONY:

Maximum CCS Ratings:

DC Plate Voltage....................................4000-volts
DC Grid #2 (screen grid).............................500-volts
DC Grid #1 (control grid)...........................-500-volts
DC Plate Current.................................... 350-ma
DC Grid #2 Input....................................  30-watts
Grid #1 Input.......................................  10-watts
Plate Dissipation................................... 500-watts

Typical Operation at 110 mHz:

DC Plate Voltage                2500   3000   4000   volts
DC Grid #2                       500    500    500   volts
DC Grid #1                      -150   -150   -150   volts
DC Plate Current                 310    310    315   ma
DC Grid #2 Current                26     24     22   ma
DC Grid #1 Current                15     16     16   ma
Driving Power (approx.)            5      5      5   watts
Useful Power Output              475    600    835   watts

For Class C Telegraphy, the ratings above are for key-down conditions
per tube without amplitude modulation.  Amplitude modulation essentially
negative may be used if the positive peak of the audio-frequency
envelope does not exceed 115% of the carrier conditions.

That's all I could find on this tube.  Hope this is of use to you.  Good
luck with your project.

73, Keith
   Grid #1 to Filament & Grid #2:  12.8 Pf

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