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by William Eric McFadden

From the Argonaut 509 manual:

The Argonaut opens a whole new world of excitement and fun in Amateur Radio. We think you will find QRP a welcome change. Five watts are only 2-1/2 S-units below 150 watts for the same conditions. When skip is favorable and QRM light, you will not be conscious of using low power.
The small size (1/5 cubic foot) makes it ideal for portable operation in a motel, camper, trailer, or mobile operation in your car, boat or plane. As a result of its low power requirements, a 12 volt lantern or automobile battery will provide many, many operating hours. An ac pack, available as an accessory, will provide 117 VAC operation. You can choose ssb or cw on any ham band between 3.5 and 30 MHz.
Specifications:

 Receiver



Sensitivity: less than 0.5 uv for 10 db signal-plus-noise ratio
Selectivity: 2.4 kHz at 6 db down; 1.7:1 shape factor at 6/50 db
Input: low impedence unbalanced coaxial input
Output Impedence: 8 ohm speaker or headphone (high or low impedence headphones can be used)
Power Ouput: 1 watt at 8 ohms with less than 2% distortion
Spurious Response more than 50 db down
Automatic Gain Control (max) for 100 db change in input signal level, output changes less than 6 db
Offset Tuning with pull-out defeat switch

 Transmitter



DC Power Input: 5 watss PEP; 5 watts CW
RF Power Output: 2 watts (50 ohm non-rative load), minimum
Output Impedence: 50 to 75 ohms
Transmit-Receive Operation: SSB: PTT
CW: complete break-in
CW Sidetone: internally switched; operates only in CW mode
Microphone Input: high impedence; crystal, ceramic or dynamic
Carrier Suppression: 40 db from single tone output
Sideband Suppression: 30 db down from a single tone output at 1000 Hz reference

 General



Frequency Coverage: 3.5 to 4.0 MHz
7.0 to 7.5 MHz
14.0 to 14.5 MHz
21.0 to 21.5 MHz
28.0 to 30.0 MHz
Frequency Stability: less than 100 Hz change from 10.5 to 14 VDC
Modes of Operation: normal sideband, reverse sideband, CW
Dial Calibration: +/- 5kHz on 80 through 15 meters; +/- 10kHz on 10 meters
Tuning Rate: approximately 25 kHz per knob revolution 80 meters through 15 meters; 100 kHz on 10 meters
Front Panel Controls: resonate, offset (pull-off), band selector, tuning knob, rf gain, af gain/power on-off, mode switch, meter switch, drive
Rear Apron Connectors: antenna, dial light switch, microphone jack, headphone/speaker jack, receiver antenna, auxillary 12v output jack, key jack, power in jack, receive/transmit antenna switch, accessories socket
Semiconductor Devices: 32 transistors, 3 MOSFETS, 3 I.C. and 18 Diodes
Power Requirements: 13-14 VDC regulated to 10% with 1 ampere load
Cabinet Dimensions: HWD 4-1/2" x 13" x 7-1/2"
Material: case: aluminum
side panels: cycolac
Net Weight: 6 pounds
Shipping Weight: 8 pounds

The Argonaut 509 was the second in the fabled Ten-Tec Argonaut series of low-power transceivers. The transceiver provides for SSB and CW operation on the 80, 40, 20, 15, and 10 meter bands with power output of about two watts. It might be argued that this rig and its immediate predecessor, the Argonaut 505, convinced the ham radio world that not only was QRP operation possible, it was fun. The Argonaut 509 originally sold for $329 and was introduced about 1973.

The Argonaut 509 was a well-designed but bare-bones CW/SSB rig. Enhancements were offered by Ten-Tec in the form of external units. These included the Model 206 100kHz Pulsed Crystal Calibrator, the Model 208 CW Filter, the Model 210 Power Supply, the Model 215P Ceramic Microphone, and the Model KR5-A Keyer. For times when a bit more power was needed, the Model 405 Linear Amplifier provided 50 watts with three watts input. As an indication of the care that the designers put into the design of this rig, the Model 208 CW filter, an external, four stage, 400Hz and 150Hz audio filter, was kept inside the AGC loop and the CW sidetone doesn't pass through the filter.

My Argonaut 509 came from the estate of NorCal co-founder Jim Cates, WA6GER, in December of 2005. Unfortunately, this classic 80m-10m CW/SSB QRP rig required service as soon as I received it. I replaced the dial-cord and, with the help of W8MHV, repaired a problem in the receiver audio chain and realigned the receiver to solve low sensitivity on several bands.

Update: The audio problem, a loud rushing noise in the speaker that isn't affected by the AF Gain control, has returned. Clearly, something in the audio chain downstream of the AF Gain control that shouldn't be oscillating is oscillating. I have not yet been successful in diagnosing this problem.

The Owner's Manual is surprisingly comprehensive to one who is familiar with manuals that accompany modern rigs. The manual contains thorough circuit descriptions, disassembly instructions, and complete alignment instructions for all circuit sub-assemblies.

Argonaut Advertisements & Brochures:

Argonaut Links:

Attributions:

Advertisement "Does a 5 Watt Transceiver..." found at Ten-Tec.
Advertisement "Experience..." found at Ten-Tec.
Brochure "New Fun..." found at K8ZT.
Advertisement "An Invitation..." (1976) scanned from orginal document.
Brochure "The Definitive QRP Rig" scanned from original document.
Brochure "...a Classic in QRPp" scanned from original document.
Brochure "What Owners Say..." scanned from original document.
Advertisement "An Invitation..." (1975) found online, source lost.