833A


The 833A is a vacuum tube constructed for medium power oscillator or class B or C amplifier applications. It is a medium-mu power triode with 300 watts CCS or 350 watts ICAS anode dissipation. The long grid and anode leads, plus high internal capacitance, limits this tube to 15-30 MHz maximum frequency. Being medium mu, it is normally not suitable for grounded grid operation.

Specifications

The 833A is a large tube of the type sometimes known as a "cookie jar" tube, with the envelope nominally measuring 116.8 mm in diameter and 219.2 mm in height. The 833A contains a thoriated tungsten filament rated at 10 volts and 10 amps. A pair of 833A's with adequate forced air cooling can deliver 1000 watts of CCS RF power operating as a class C amplifier plate modulated stage.
A pair of tubes used in a class B modulator can deliver 1800 watts of "peak" AF power in ICAS service with speech, or 1600 watts in CCS service with music or high duty cycle operation. Two 833A's are capable of approximately 800 watts sine wave power in a class B audio amplifier or modulator. This assumes approximately 58% efficiency, 1400 watts input, and 300 watts per tube anode dissipation. The anode normally shows a dull to medium red color when operating at full power.
The tube is supported solely by its two filament posts. These posts are keyed with the F1 and F2 connection having a diameter of 9.5 mm and 11.1 mm respectively.
The 833A was preceded by the 833.

Characteristics

Amplification factor, 35

Anode to Grid capacitance, 6.3 pF

Anode to Filament capacitance, 8.5 pF

Filament to Grid capacitance, 12.3 pF



Values for two 833s working class B as an audio amplifier or modulator.

Va max, 3 kV

Ia max, 500 mA

Pin max, 1.125 kW

Pa max, 300 W

Vg1 max, -70 V

A.F. grid to grid voltage, 400 V Pk.

No signal D.C. anode current, 100 mA

Max signal D.C. anode current, 750 mA

Load resistance,, 2.375 kΩ

Effective load resistance,, 9.5 kΩ

Max signal driving power, 20 W avg.

Max output power, 1.65 kW avg.



Values per 833 working class B as an R.F. amplifier with a maximum modulation factor of 1.0.

Va max, 3 kV

Ia max, 400 mA

Pin max, 450 W

Pa max, 300 W

Vg1 max, -70 V

Peak R.F. grid voltage, 90 V.

D.C. anode current, 150 mA

D.C. grid current, 2 mA

Driving power, 10 W appx.

Output power, 150 W appx.



Values per 833 working class C as an R.F. amplifier with a maximum modulation factor of 1.0.

Va max, 2.5 kV

Ia max, 400 mA

Pin max, 850 W

Pa max, 200 W

Vg1 max, -500 V, nom, -300v

Peak R.F. grid voltage, 460 V.

D.C. anode current, 335 mA

D.C. grid current, 75 mA

Driving power, 30 W appx.

Output power, 630 W appx.



Values per 833 working class C as an R.F. amplifier or oscillator,

Va max, 3 kV

Ia max, 500 mA

Pin max, 1.25 kW

Pa max, 300 W

Vg1 max, -500 V, nom, -200 V

Peak R.F. grid voltage, 360 V.

D.C. anode current, 415 mA

D.C. grid current, 55 mA

Driving power, 20 W appx.

Output power, 1 kW appx.



Grid voltages measured with respect to the midpoint of the directly heated cathode.

80% efficiency at A.F., dropping to 60% at 100 MHz when used as an amplifier.

Applications

The 833A was widely used in small AM broadcast transmitters. Typically, a pair of 833As would be used in the final amplifier, plate modulated by another pair. It was also used in small induction heaters. This tube has also been used by hobbyists to construct a vacuum tube Tesla coil.