PHILIPS 6FZ-259/10


photo Philips 6FZ-259/10 These transmitters have been specially designed and built to ensure the maximum of simplicity and economy of operation plus high stability and audio fidelity. They are fully tropicalized and suitable for continuous operation under severe climatic conditions.

The most important measuring instruments, command switches, signalling lamps and tuning controls, with their functions clearly indicated, are fitted on a front panel permitting the technical staff to easily check the performance of the transmitter during normal operation.

The limited number of electronic tubes employed, all of commom use, reduces to a minimum the stock and replacement profolems.

Excellent sound fidelity is obtained by using negative feedback and transformers of the highest quality. All tubes operate well within their no minal ratings resulting in longer useful life and lower noise and distortion levels.

Front and rear doors give complete access to all components, most of them mounted on vertical panels. Both doors are provided with ample windows so to observe the interior of the transmitter while the equipment is in normal operation or during servicing and tuning.

Complete protection to the operating personnel and to the equipment is ensured by means of a system of automatic switches, magnetic interruptors and safety relays and switches. Interlock switches disconnect the high tension automatically when any of the two doors is opened.

Two versions are available, one for medium waves, type 6FZ-259/00, and the other for intermediate and short waves, type 6FZ-259/10. Both versions have facilities for reduced power operation in 500 watts by simply throwing a built-in switch.


These broadcast transmitters are composed of four main sections, namely: radiofrequency, audiofrequency, power supply and control and protection, as follows:


In the medium-wave transmitter type 6FZ-259/00 the RF section is equipped with a highly stable Pierce oscillator, using a 6CL6, with aperiodic plate circuit. The quartz crystal is housed in a thermostatically-controlled oven. Fine frequency adjustment is possible by means of a variable capacitor connected to the grid of the oscillator tube.

The oscillator signal is applied to an amplifier-exciter stage, using one QE-05/40 (6146) with tuned plate circuit, which drives the class C final stage composed of two tubes QB4/1100 (4-400A) connected in parallel.

The aerial output circuit is suitable for direct feeding of 1/8 to 1/4 wavelength vertical radiators or, on request, for connection to an unbalanced feeder line with impedance between 50 and 330 ohms. For this case an aerial matching unit is optionally available. A built-in RF ammeter in the transmitter measures the RF output current.

In the intermediate and short- wave transmitter type 6FZ-259/10 the oscillator stage is also of the Pierce type but with tuned plate circuit, being the oscillator frequency half the operating one. Fine adjustment facilities are also provided.

The amplifier-exciter stage has its plate circuit tuned to twice the oscillator frequency acting therefore as a doubler and driver of the class C final stage composed of two QB4-1100's connected in parallel. The required plate neutralization for the final stage is provided by means of a capacitor.

The aerial circuit, inductively coupled to the final RF stage, is suitable to feed a 600-ohm balanced feeder line. The aerial current is measured with a built-in RF ammeter.


The AF sections of the two transmitters herewith described are exactly equal.

The AF input signal is fed, via an input transformer, to a class A balanced amplifier stage consisting of one ECC82 (12AU7).

From the input stage the AF signal passes through the phase correctors to the intermediate amplifier stage composed of two tubes EL-90 (6AQ5) operating in a class B balanced circuit.

Once amplified to the proper level, the AF information is applied to the final modulator stage comprising two QB4/1100's in a class B balanced circuit.

The AF signal present in the modulator anodes is transferred to the final RF stage by means of a high quality modulation transformer and related modulation reactor.

The modulation transformer is provided with a terciary winding used to apply to the grids of the AF input stage the negative feedback required to keep to a minimum the distortion level.

The AF input level is adjusted and the modulator dynamic currents are balanced by means of two separate potentiometers.


These transmitters are built to operate from power mains of 220 volts, three-phase, 50 and 60 Hz.

They are provided with three power supplies and related filtering elements, namely:

  1. "- C" supply, to furnish negative bias to the grids of the tubes QE05/40 and QB4/1100 and to the "- C" minima protection relay, using two diodes 0A211 in a full-wave monophase rectifying circuit.

  2. Low tension supply, to feed the screen-grids and anodes of the small tubes (6CL6, EL90, ECC82, QE05/40) and the screen-grids of the QB4/1100's, using eight diodes 0A211 in a bridge rectifying circuit.

  3. High tension supply, furnishing anode voltage to the final RF and modulator tubes QB4/1100, composed of three rectifier tubes DCG5/5000GB (872-A) in a half-wave threephase rectifying circuit.


The transmitters are equipped with four pilot lamps, nine measuring instruments and a system of command switches, safety relays, magnetic interruptors, fuses, etc., providing extensive metering and control facilities.

The nine meters are intended to measure the following:

  1. Grid current of the final RF tubes.

  2. Cathode current of the final RF tubes.

  3. High tension.

  4. &
  5. Cathode current of each one of the final modulator tubes.

  6. Tension on each of the three mains phases by using a three-position selector switch.

  7. By means of a three-position switch:

    1. Total cathode current of the AF input amplifier.

    2. Total cathode current of the AF intermediate amplifier.

    3. Output voltage of the low tension supply.

  8. By means of a three-position switch:

    1. Cathode current of the oscillator stage.

    2. Cathode current of the amplifier-exciter stage.

    3. Screen-grid current of the final RF tubes.

  9. Aerial current or RF output current.


The transmitter cabinet houses all components, the heavy ones being mounted on a chassis on the bottom and the remainder on two vertical panels.

The spacious design simplifies maintenance and serviceability, which is further enhanced by the front and rear doors provided with ample windows.

The various controls, pilot lamps, final stage tuning and measuring instruments are logically arranged on the transmitter front.

The cabinet top, provided with ventilating louvers, supports the RF output isolators. Adequate cooling of the final RF and modulator tubes is obtained by means of two fans mounted close to them. A two-tone gray finishing gives to the equipment a pleasing and modern appearance.

Application Commercial continuous broadcast service
Power output (unmodulated carrier) 1,000/500 W nominal
Frequency of operation one, within the band of 2.3 to 17.9 MHz
Mode of emission 20A3
Frequency control By quartz crystal mounted in thermostatically-controlled oven
Frequency tolerance ± 0.003%
Output circuit 600 ohms, balanced
Type of modulation High level, class B
AF input impedance 600 ohms balanced
AF input level + 10 dbm at 100% mod. (1,000 Hz)
Modulation capability 100% (from 50 to 10,000 Hz)
Linear distortion Flat, within ± 1.5 dB from 50 to 10,000 Hz, reference 1,000 Hz
Non-linear distortion Less than 3% from 50 to 7,500 Hz, up to 90% modulation
Noise-level Better than -54 dB, unweighted, reference 1,000 Hz at 100% modulation
Power supply 3 x 220 V, 50 or 60 Hz
Thermal oven supply 110/220 V, monophase, 50/60 Hz
Power consumption 1) Thermal oven: 24 VA
2) Transmitter, 100% mod.: 3.7 Kw (1,000 W output); 2.3 Kw (500 W output)
Power factor 0.92 approx.
Ambient temperature From 0° to + 45°C, at sea level
Relative humidity Up to 95%
Dimensions Height: 210 cm (82 in.)
Width: 90 cm (35 in.)
Depth: 88 cm (34 in.)
Weight, less tubes (unpacked) 545 kg (1,200 lb.)

RF stages AF stages and modulator Rectifiers
Number Type Number Type Number Type
2 QB4/1100 (4-400A) 2 QB4/1100 (4-400A) 3 DCG5/5000GB (872A)
1 QEO5/40 (6146) 1 ECC82 (12AU7)

1 6CL6 2 EL90 (6AQ5)


ITU Country
ITU Country