The service manual for the Hammarlund FM-50-A VHF receiver-transmitter provides detailed instructions for installation, operation, and troubleshooting, including the use of external controls such as volume and squelch, and the operation of the power switch and push-to-talk microphone switch. It also emphasizes the importance of proper system installation and correct operating procedures to ensure efficient and reliable communication over long distances.
Manual Overview
The Hammarlund FM-50-A service manual provides detailed instructions for troubleshooting, diagnostics, calibration, and adjustments of the VHF receiver-transmitter. The manual emphasizes a systematic troubleshooting flow, starting with checking power supply connections and ensuring correct voltage levels for both AC and DC operations. Error codes and diagnostics are not explicitly detailed, but technicians are advised to verify component functionality, particularly focusing on the tube and semiconductor complements. Calibration involves adjusting the squelch control for optimal sensitivity and ensuring frequency stability within the specified range. Board-level guidance includes verifying the integrity of the crystal oscillator and phase modulator circuits, as well as ensuring proper operation of the frequency multipliers and RF power amplifier. The manual also outlines the importance of maintaining the correct duty cycle to prevent overheating and ensure longevity of the device. Regular checks and adjustments are recommended to maintain performance and reliability of the FM-50-A unit.
Quick Issues Covered
- Diagnose power-up failures with voltage checks at power input terminals.
- Calibration of squelch sensitivity using front panel control adjustments.
- Circuit tracing with detailed schematics for RF and audio sections.
Overview
The FM-50-A is a rugged, compact communications unit designed for narrow-band phase/frequency modulation operation in the frequency range of 147 to 174 megacycles. It can operate from any 6 or 12 volt d.c. vehicle power source or a 117 volt a.c. land station power source. The unit is designed for single channel, crystal controlled operation, with the ability to operate the transmitter and receiver on the same or different channels. It features a simple control interface with a volume control, squelch control, and a three-position power switch. The manual covers installation, operation, and service instructions for the FM-50-A model.
Specifications
- Frequency Range: 147 to 174 Mes, on any single channel (not necessarily the same for receiving and transmitting)
- Transmitter:
- FCC File # Hammarlund Type FM-50-A
- Power Output into 50 ohm load: 117V AC operation, 35 watts (+10%)
- 12V DC operation, 30 watts (410%)
- 6V DC operation, 20 watts (410%)
- Duty Cycle: 117V AC – 1 min, on, 1 min. off
- 12V DC – 1 min. on, 4 min, off
- 6V DC – 1 min, on, 4 min. off
- Crystal Multiplication: Twelve Times 6
- Frequency Stability: 0.0005% (-30° to + 60 C ambient temperature range) OVEN CONTROLLED
- Modulation: 16F3, +5Ke deviation for 100% modulation at 1000 cps
- Modulation Limiting: Instantaneous and automatic, .25V rms input at 1000 cps for thresh-hold of limiting
- Audio Response: +1 to -3 db from 300 to 3000 cps, 1000 cps reference
- Distortion: Less than 10% at 3.5 Ke deviation, 1000 cps modulating frequency
- Spurious & Harmonic Radiation: At least 60 db down
- Hum & Noise: At least 40 db below +3.3 Ke deviation, 1000 cps reference
- Receiver:
- Frequency Stability: See transmitter specifications above
- Sensitivity: 0.5 microvolt or less for 20 db quieting
- Selectivity: +5 KC (or greater) at 6 db down
- +17 KC (or less) at 100 db down
- Spurious Response Attention: At least 90 db down
- Intermodulation Spurious Attention: At least 65 db down
- System Audio Response: +2 db from 300 to 2500 cps, 1000 cps reference
- Audio Output: At least 1.0 watt at less than 10% distortion into built-in speaker
- Hum & Noise Level Squelched, at least 50 db down from rated output Unsquelched, at least 40 db down from rated output
- Squelch: Signal to noise ratio type, front panel adjustable, .15 microvolt or less at thresh-hold
- Duty Cycle: Continuous
- Crystal Frequency Formula: Signal Frequency -10.7 MC
- Tube Complement
- 6BS8 Receiver Cascode RF Amplifier
- 6BR8 1st Oscillator/Multiplier and 1st Mixer
- 6BR8 1st IF Amplifier (10.7 mc) and Squelch Noise Amplifier
- 6BR8 2nd Oscillator and 2nd Mixer
- 6 BH6 2nd IF Amplifier (1.65 mc)
- 6BH6 1st IF Limiter
- 6BN6 2nd IF Limiter and FM Detector
- 12AX7 1st Audio Amplifier and Squelch DC Amplifier
- 6AQ5 Audio Power Amplifier
- 6BR8 Transmitter Crystal Oscillator and Phase Modulator
- 6AW8A Buffer and 1st Frequency Multiplier
- 6360 2nd and 3rd Frequency Multipliers
- 6146 RF Power Amplifier
- 12AX7 1st and 2nd Audio Amplifiers
- Semi-Conductor Complement
- IN 248
Controls & Indicators
The front-panel controls of the FM-50-A include a conventional volume control knob on the left, a squelch control knob on the right, and a three-position power switch. The power switch has settings for “OFF,” “STDBY” (standby), and “OPERATE.” There are also two pilot lamps: one on the left side of the power switch that lights when the set is turned on, and another on the right side that lights when the transmitter is on the air.
Installation / Setup
Refer to the PDF for details.
Operation
The FM-50-A VHF Receiver Transmitter is designed for operation from 6 or 12 volt DC vehicle power sources or a 117 volt AC land station power source. It operates in the frequency range of 147 to 174 megacycles with narrow-band phase/frequency modulation. The unit is equipped with three external controls: a volume control, a squelch control, and a three-position power switch. The power switch has “OFF,” “STDBY,” and “OPERATE” positions. In “STDBY,” only the receiver is active, while in “OPERATE,” both the receiver and transmitter are active. The transmitter is activated by a “push-to-talk” switch on the microphone. The unit is efficient and reliable for long-distance communication, with optimal performance depending on factors like antenna height and terrain. Proper operating procedures include checking the channel before transmitting and training mobile operators to call the base station from good locations.
Troubleshooting & Error Codes
Refer to the PDF for details.
Safety & Warnings
Refer to the PDF for details.
Download MANUAL Service manual (PDF – 1.6 MB)
Hammarlund FM-50A Manual: Provides technicians with installation, troubleshooting, and calibration guidance. PDF size: 1.6 MB.
- Brand: Hammarlund-fm-50a-installation-service
- Model: MANUAL
- Type: Service manual
- File size: 1.6 MB
Overview
Brief overview of the product.
Specifications
- Key spec 1
- Key spec 2
Controls & Indicators
Control panel/button layout.
Installation / Setup
- Step 1…
- Step 2…
Operation
Basic usage, modes, cycles.
Troubleshooting & Error Codes
| Issue / Code | Fix |
|---|---|
| Example | How to fix… |
Safety & Warnings
- Important warning…
Downloads
Download MANUAL service manual (PDF)
Hammarlund FM-50A Installation and Service Manual Overview
The Hammarlund FM-50A is a classic communications receiver renowned for its robust design and reliable performance. Primarily used for shortwave and AM broadcast reception, this device serves both amateur radio enthusiasts and professional operators. The FM-50A excels in delivering clear audio reception across a wide frequency range, making it an essential tool for monitoring and communication tasks.
Main Features and Specifications
- Frequency Coverage: 540 kHz to 30 MHz
- Superheterodyne Receiver with Multiple IF Stages
- AM and CW Modes Supported
- High Sensitivity and Selectivity
- Built-in BFO (Beat Frequency Oscillator) for CW Reception
- Analog Tuning Dial with Calibrated Scale
- External Antenna and Speaker Connections
- Durable Metal Chassis for Long-Term Reliability
Basic Usage and Operation Tips
To operate the Hammarlund FM-50A, first connect a suitable external antenna to maximize signal reception. Power on the unit and select the desired frequency band using the band switch. Adjust the tuning dial slowly to locate the signal of interest. Use the BFO control when listening to Morse code (CW) transmissions to improve clarity. For best audio output, connect an external speaker or headphones. Regularly calibrate the tuning dial using known frequency markers to maintain accuracy.
Troubleshooting and Maintenance Notes
If you experience weak or distorted signals, verify antenna connections and inspect for any damaged cables. Ensure all tubes and components are seated properly and replace any faulty vacuum tubes as needed. Clean the tuning capacitor and switches periodically to prevent static and improve performance. If the receiver fails to power on, check the fuse and power supply connections. Refer to the alignment procedures in the manual to maintain optimal receiver sensitivity and selectivity.
Safety Reminder
Always disconnect the receiver from the power source before performing any maintenance or internal inspections. Avoid contact with high-voltage components inside the chassis to prevent electric shock. Use caution when handling vacuum tubes, as they can become hot during operation. Follow all safety guidelines outlined in the manual to ensure safe and reliable use of the Hammarlund FM-50A receiver.
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