Portable Shortwave Receiver
<Sorry, no Japanese Page>
In the shortwave boom of middle 1970s the competition between Sony SkySensor
and Panasonic Cougar became hot, and other big players of consumer electronics
joined to the theater of shortwave portables. Toshiba offered
Although the built-in CAL marker and scale ring surrounding the tuning knob provided easier tuning and better frequency readout accuracy, the Try-X 1600 was considered as the pure beginner's class, as it covered only up to 12MHz, no BFO, no bandspread mechanism. It even missed the external antenna terminal which was essential for the DXing. Later introduced Try-X 2000 was really fantastic, but I never had a chance to get Toshiba radio until I got this particular unit.
The Try-X 1600 is a quite basic AM-FM-SW 3 band portable. It runs from 3 C cells or AC100V; power transformer is built in.
On the right side of the front panel, there are POWER switch, BAND SELECT, Volume control and TONE control.
Above the speaker there are, from left to right, LOUDNESS switch, FM-AFC / MW-DX-LOCAL switch, and the CAL switch.
Single tuning knob has a "tuning ring" on which the bandspread scales are printed.
The ring is normally rotates with the knob, but it can be rotated while holding the tuning knob.
When precise frequency readout is desired, you follow the following steps;
Dial mechanism is of average transistor portables. Far from pleasant touch for the shortwave tuning.
DIAL LIGHT is a momentary switch turns on a small lamp, illuminating the tuning dial.
Like most of the low priced portables, it only provides minimum illumination.
Its construction is very simple, as shown: an example of the low-priced consumer product.
Tuning indicator shows the relative strength of the incoming signal. It goes right as the signal getting stronger. The meter itself is reverse going; it points rightmost when power is turned off.
The radio has AC power jack on the back, EARPHONE and TIMER jack on the left side.
The unit is miserably dirty outside and even inside.
Broken AFC switch lever and missing top of the rod antenna are the physical problems.
The circuit is mostly discrete except one IC, seems to be an audio preamplifier. A FET is used, possibly a shortwave RF amplifier. I don't have technical information of this radio so I cannot tell until I study it more.
Quick check revealed the receiver is completely dead. It keeps silent, meter does not respond, even the dial light does not light up. It may be a simple problem such as disconnected wiring or something.
However I found one small coil or transformer was missed from the circuit board. It looks that someone "pulled" the coil brutely from the board without using soldering iron; terminal pins and remaining of some thin copper wires are observed. Obviously, it was abused.
Dial film was largely misaligned.
It was apparent that someone opened the radio, partly disassembled, and re-assembled imperfectly.
The rod antenna did not shine. Metal polish worked fine with this.
Before throwing away this dirty stuff I thought I should at least find why the radio is completely dead.
Connecting the battery directly to the circuit board, I found the circuit was functional.
Tuning indicator moved, pop noise was heard from the speaker.
Applying Safe Wash spray revived the radio, at least for AM and FM.
The reason of complete deadness was simple; a TIMER jack had a bad contact. This low priced radio does not have a mechanical sleep timer which was very popular among the midnight AM listeners. Instead, it has a TIMER jack, and optional external timer could be connected. The jack is a standard mini-jack. If an external timer is not plugged in, two contacts of the jack should conduct so that the power supply voltage is fed to the circuit. After the contact was cleaned, the radio started to play from the battery installed to the battery compartment.
The performance of AM and FM is quite satisfactory. Sensitivity is good, the sound is nice with plenty of volume. If a good external speaker is used, pleasant audio can be enjoyed.
The radio seems to be economical to run; it keeps to play with acceptable volume, even when the battery voltage drops to 2.5V, although the sound becomes distorted. Even at 2.2V, sound remains intelligible. Battery drain measured less than 20mA. It continued to play for more than 5 days with batteries which were already dead for a bicycle halogen headlamp.
SW band, however, was still dead. By locating another shortwave radio nearby,
I confirmed that the local oscillator of this radio was operational.
By flicking the CAL switch to ON, I heared the oscillator noise at every 1 MHz.
Static noise also indicated the operation of the converter and following circuits.
Tracing the circuit quickly, the missing coil was found to be a shortwave RF coil. The primary winding should be connected to one section of the tuning cap, and the secondary seemed to be connected to the converter stage. When 455kHz signal from a signal generator was fed to the secondary, the audio was heard. There was a RF amplifier stage which used a 2SK19 FET. The input of the RF amp seemed to be untuned.
The reason why someone pulled out the coil is a mystery. The soldering points were intact; no attempt of modification found. I guess the owner wanted to expand the frequency range to cover 15MHz band, because I also really wanted to do so to my National (Panasonic) RF-877 when I was 10 years old. But if he/she knew this was the coil to be modified, he should have known how to use a soldering iron too.
Knowing it was futile, I tried some coils such as AM radio IFT. The radio started to receive something, but it was nothing but ghost of various FM stations, TV sound, and computer noises. Without technical information, winding an appropriate coil will be an exhaustive task, apparently too much for this dirty receiver. It seemed best to leave it as an AM/FM radio. But if someday similar junky shortwave radio is found, there would be a chance for this 1600 to be completely revived. If it becomes clean and fully operational, it'll be a fun bedside radio. But it will be a long way.