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 Previous: Project Goodwill Doubles Albania's Ham Population |  Next: Kid's Day is Sunday, January 4! |
By Louis L. D'Antuono, WA2CBZ
December 16, 2003
Used separately or together in a transceive configuration, this mid 1960s setup made for a satisfying first station.
 The SX-146 and HT-46 can be coupled together to share a VFO for transceive operation. [Photos by the author] |
Even before I received my Novice license in 1975, I decided to select a communications receiver for my station. I went down to Harrison Radio to purchase a used model. At that time, the store was located on Barclay Street in New York City. After reviewing a number of popular units, the salesman suggested I purchase a Hallicrafters SX-146 receiver, with which I was unfamiliar. He explained its usefulness for code practice and sideband reception because it featured a product detector. After surveying a number of QST past issues, I learned that it had been manufactured by Hallicrafters in late 1965 and first advertised in said magazine in January 1966. At the same time, Hallicrafters produced a companion transmitter, the HT-46, which I subsequently bought in 1976. These units formed the basis of my first amateur station and they always performed excellently whenever I used them. Higher priced models did perform better, but for compactness, versatility and simplicity, the SX-146 and HT-46 are exceptional.
What I first noticed about the SX-146 receiver was that it
was a lot smaller than comparable units. During the early 1960s, Hallicrafters
began to make its units with a lower profile in mind, similar to other
manufacturers such as Collins and Heathkit. The SX-117 receiver and the HT-44
transmitter, produced in 1962, were much taller. Both had the ability to be
used separately, or together for transceive operation. The main difference was
that the larger units had more standard accessories than the smaller ones.
These included items such as VOX, WWV reception, a 100 kHz crystal calibrator
and an optional low frequency converter. The fact that the smaller units did
not have these standard features did give me some pause, but their compactness
and lower profile that made them so appealing. At the time, my only concern was
future sideband capability and any receiver that brought me there was the order
of the day.
 The SX-146 covers all frequencies between 2 and 30 MHz with an external oscillator, with the exception of the rig's intermediate frequency of 9 MHz. |
The Receiver
The SX-146 is a single conversion receiver that was designed primarily to cover the 80 through 20 meter ham bands. It utilizes nine vacuum tubes and a silicon diode power rectifier. The tube lineup is:
The power supply has a non-tapped secondary feeding into a half-wave rectifier, followed by three high capacity electrolytic capacitors and two resistors. Hum is negligible with headphone use. The only unusual feature is that there is no voltage regulator for the oscillators. Communications receivers of higher quality often have this feature, but in the case of this receiver its absence does not seem to be a problem.
Aside from its ham band coverage, the radio can cover any frequency between 2 and 30 MHz with an external oscillator, with the exception of 9 MHz. The intermediate frequency is 9 MHz, which virtually eliminates images. There is one loud birdie at 21.350 MHz. There is a standard six pole 2.1 kHz crystal filter for selectivity between the mixer and the first IF amplifier stages. In practical receiver design this puts the main selectivity as close to the front end as possible. The oscillator section tunes 5.0 to 5.5 MHz and with heterodyning internal crystals it can cover the higher frequencies.
It uses a slide rule dial that is nearly linear on all
bands. The only unusual feature of this dial is that while the 80 and 40 meter
bands tune from left to right, the 20, 15 and 10 meter bands tune from right to
left because of the heterodyning frequency conversion. The receiver also features
a vernier tuned preselector. Some operators might find the tuning rate too fast
and the size of the tuning knob too small and too low on the receiver front
panel.
 Rated at 175 W PEP on SSB and 150 W on CW, the HT-46 uses a 12HY7 driver followed by a 6HF5 power amplifier. |
The Transmitter
The HT-46 transmitter is a mirror image of the SX-146 receiver and serves a dual purpose. It can be used as a standalone transmitter or in conjunction with the receiver. It can also function as a transceiver with the SX-146 by using that radio's internal oscillator. There is a front panel slide switch that selects either of these choices. Before transceive operations are accomplished, a slight internal adjustment is required. Alongside this switch, there is a calibration slide switch that provides a low level signal for zero beating. In terms of power input, the transmitter is rated at 175 W PEP on SSB and 150 W on CW.
The transmitter uses nine tubes and a silicon rectifier power supply. The tube lineup includes a 6BA6 VFO, a 6EAS heterodyne crystal oscillator and mixer, a 12AT7 carrier oscillator-third audio; a 12AT7 microphone amplifier, a 6EA8 9 MHz IF amplifier and ALC; a 6AH6 mixer, a 12HY7 driver, a 6HF5 power amplifier and an OA2 voltage regulator. The power supply begins with a center-tapped power transformer that feeds into a bridge rectifier with the center tap providing the half-voltage output. Lower voltages are derived from this source as well. A separate winding on the transformer using a half-wave silicon rectifier provides the negative bias voltage.
The HT-46 uses the same frequency generation system as the SX-146 receiver by using a local oscillator with internal crystals. The keying method is grid-block and sideband generation is of the filter type. Push-to-talk operation is provided and there is provision for VOX control. An internal relay furnishes muting for the receiver as well as contacts for an external relay needed for a single antenna. The self-contained relay is activated by the transmitter's rotary operation switch. Voltage for this dc relay comes from the filament supply into a half-wave rectifier. The only feature that the transmitter lacks is a variable loading control in the Pi-Output network. Instead, it uses a fixed mica capacitor network designed to match a 50 Ω impedance antenna for all bands.
Accessories and Operation
Fortunately, there are many accessories available to enhance the performance of these units. There are the additional crystal filters for the receiver, including a 500 Hz for CW and a 5 kHz for AM. Both of these plug into the chassis without any wiring changes. Additionally, there is a matching R-51 3.2 Ω speaker that contains a 24 hour digital mechanical clock. More common is the R-50 speaker, which is similar in appearance to the R-51 without the time display. Other speakers with similar impedance can be utilized. For checking dial accuracy, there is an optional 100 kHz crystal calibrator that plugs into the receiver chassis without wiring changes and is activated by a front panel slide switch. There is an optional VOX for the transmitter that mounts on its back panel and plugs into the rear chassis. Transmitter power can be boosted by coupling it to any of the numerous Hallicrafters linear amplifiers such as the HT-41 or HT-45 or any similar model with a 50 Ω input impedance.
Both of these units performed superbly the first time I fired them up. The initial thing I noticed was that the product detector made copying sideband and deciphering Morse code easier. This was a big improvement over my Hallicrafters S-29 Sky Traveler, which required turning down the RF gain control and increasing the AF gain to hear SSB and Morse well. The stability was good and the selectivity provided by the standard crystal filter was impressive. At certain times, though, I wished for greater sensitivity to copy DX. To solve the shortcoming of the main tuning knob's small size, I substituted a larger National brand knob and raised the height of the receiver.
The transmitter performed just as well as the receiver. All of the signal reports I received were satisfactory, although I often toyed with the idea of using a linear amplifier for DX. An Ultimate Transmatch solved the problem of the antenna impedance matching capability that was lacking because of its fixed loading output.
With today's increased practice of split frequency operation, these radios will not miss a beat, and it's easy enough to switch between running in transceive mode or separate units.
Louis D'Antuono, WA2CBZ, holds an Amateur Extra license
and teaches social studies at James Madison High School in Brooklyn, New York.
| Previous: Project Goodwill Doubles Albania's Ham Population | Next: Kid's Day is Sunday, January 4! |
