Model HF-50 C

photo Gates HF-50 C The Gates HF-50 C high frequency broadcast transmitter is high level plate modulated and capable of delivering 55,000 watts of power into a balanced line of 300-800 ohms on any frequency between 4-30 MCS. Outstanding advantages of the HF-50 C are: small, compact size requiring a minimum of floor space-transmitter proper only 6.5 ft. high, 11 ft. wide, 61 5/8 inches deep; rapid frequency change; interchangeability of PA and modulator tubes; less tube types; longer tube life; and low power consumption-only 100 KW at average programming. Introduced in 1959, following wide acceptance of similar models now in use at station ELWA, Morovia, Liberia and the Dominican Republic, the HF-50 C has been especially designed to operate in world wide climates and for the most rigorous demands of continuous duty.

CONSTRUCTION: The HF-50 C consists of three main cubicles; audio driver and modulators, RF exciter-driver control cubicle and power amplifier cubicle. All cabinets are accessible from front and rear and vertical construction design permits easy servicing.

RADIO FREQUENCY SECTION: The exciter RF/driver along with associated separate power supplies are built into the center cubicle. Rated at 85 watts output, the exciter has a crystal selection system with 10 positions selectable from the front panel. (Dual exciter units can be provided where desired.) The 3KW driver is continually adjustable and is very conservatively rated which provides reserve power for driving the final amplifier.

POWER AMPLIFIER SYSTEM: The power amplifier uses two Federal Type 6804 forced air cooled tubes in push-pull. Since one tube is capable of delivering 50 KW output, a tremendous reserve of power is available.

AUDIO SYSTEM: All audio stages are located in the modulator cubicle. The 1st audio stage uses two 6146 tubes push-pull. The 2nd audio stage uses two 813 tubes operating as a push-pull amplifier. The audio driver stage uses two 833A triodes operating in a direct coupled cathode follower circuit. Adjustment of bias resistors, feedback and carrier hum are simple. Over-all feedback is approximately 15 db an optimum value for minimum distortion and noise.

MODULATION: Type 6804 tubes used in the PA system are also used as modulators. High level plate modulation is used in the HF-50 C transmitter, which provides for a constantly available reserve of audio power. The HF-50 C modulator is designed for continuous duty at extremely high levels of average modulation in order to provide for the most possible coverage for this transmitter power.

POWER SUPPLIES: All power supplies in the HF-50 C transmitter utilize silicon rectifiers for long trouble-free service throughout a wide range of temperature and humidity. This includes the main high voltage rectifier which provides approximately 10.5 KV plate for the final amplifier and modulator tubes. The use of silicon rectifiers in the design of the HF-50 C has provided a 50 KW HF broadcast transmitter with a minimum space requirement. Separate high voltage plate transformers are used to provide for easier installation and more dependable service.

CONTROL: The HF-50 C is provided with a generous supply of overload and under-voltage relays. Every circuit large or small is protected most adequately.

INSTALLATION: The HF-50 C has been designed for maximum installation flexibility to fit various situations. It can be supplied with either internal or external blowers to meet your exact installation needs. Gates engineers are available to assist in the installation planning at all times.


INTERNAL OR EXTERNAL BLOWERS: The HF-50 C is 100% air cooled with either internal or external blowers. This is a Gates exclusive made possible by very careful and detailed mechanical design. With internal blower arrangements a 3 ft. wide cubicle is added to the right side of the PA cubicle for PA cooling. This increases over-all length to 14 ft. Modulator and driver cubicle have self-contained blowers. No changes in transmitter proper are necessary for external blower arrangement. Air is controlled to insure maximum cooling of all critical areas. Exhaust can be vented out of the building or used for heating in winter.

REGULATION: Filament voltages for the entire transmitter are regulated. This is handled by a Gates three-phase voltage regulator with electronically controlled motor driver transformers keeping filament voltage within 1/2% at all times.

METERING: 14 meters are provided. 8 are located along the top of the power amplifier and modulator cubicle. 5 are located along the upper panel of the exciter RF/driver cubicle. The 14th meter is a multi-meter on the 85 watt exciter unit, which provides for complete metering of the oscillator and RF amplifier stages up to the driver stage. Easy, quick readings can be taken at any time.

BAND SWITCHING: A new concept of plate tank circuit design makes necessary only one adjustment other than from the front panel, to provide for continuous coverage over the range of 4-30 MCS. No plug-in coils are used in the HF-50 C transmitter and frequency change can be accomplished in less than five minutes.

Power Output 50,000 watts
Output Impedance 300-800 ohms balanced
RF Range 4-30 Mc
Frequency Stability Capable of .003% or better
RF Harmonics Meets or exceeds FCC requirements
Audio Frequency Response 85% modulation (50-10,000 cycles) ±1.5 db
Audio Harmonic Distortion (0-95% modulation from 50 to 7500 cycles) 4% or less
Audio Input 100% modulation sine wave, 400 cps. +10 dbm
Audio Input Impedance 600 ohms
Primary Voltage 460 volt, 50/60 cycle, 3-phase
Power Consumption Carrier 90 Kw at 90% PF, Average Program 100 KW at 90% PF 100% modulation 135 KW at 90% PF
Carrier Shift (100% modulation with 400 cps) 5% or better
Total Number of Tubes 21
Total Tube Types 13
Size 6.5' high, 11' wide, 5' deep (with external blower)
6.5' high, 14' wide, 5' deep (with internal blower)
Weight 26,850 lbs. packed wt.; cubage 1480 with external blower
26,859 lbs. packed weight, cubage 1555 with internal blower
Crystal H17 crystal unit JK 02, 6.3 volt A.C., heater oven
Modulation Capability (30-7500 cycles) 100%. High level class "B"
Radio Telephone Model This model is available for radio-telephone service as desired
Radio Telegraph Model The Gates HF-50TX radio-telegraph transmitter is identical to the transmitter described
herein except it does not include the modulator cubicle.
It is designed for high-speed keying or FSK service.
Size is 4 ft. narrower than broadcast model. All other details are the same
Specifications may change without notice

RF stages AF stages and modulator Rectifiers
Number Type Number Type Number Type
2 F-6804 2 F-6804 2 5R4GYA
1 6076 2 833A 1 6AL5
2 6146 2 813

2 5763 2 6146

1 OB2

1 6AQ5


ITU Country
ITU Country