I bought a LS-166/U military loudspeaker in good general conditions recently. According to labels on it, my LS-166/U was made in Italy by LA.RI.MA.R.T., in Rome.
I bought the LS-166/U with the aim of adapting it as the external loudspeaker for my russian R-326 military receiver.
As you may well know, the R-326 (or P-326 according to the russian alphabet) is a nice small receiver, which can operate both from batteries and from AC mains (by means of its power supply). It started to be produced in early '60s. It employs 19 miniature tubes and requires only about 1.5A at 2.5V to operate, which is surprisingly a low power requirement for a tube receiver of its complexity.
The R-326 receiver (from http://air-radiorama.blogspot.com)
The R-326 does not feature an internal speaker. It has a 600 ohms audio output, in the form of a bipolar socket in the lower part of the front panel, that can be used for connecting both heaphones and a 600 ohms external speaker.
Let me say that the original, heavy duty, military headphones that came with my R-326 are not the best you could desire in terms of comfort. So I started to think about how to connect more modern, light and comfortable low-impedance headphones to the radio. First, I looked around for a 600 ohms to 8 ohms transformer to build a simple impendance and connector adapter, then I thought that it could be nice sometimes to have a chance to listen to the radio by an external loudspeaker, possibily a military one. The LS-166/U appeared to be well suitable for my purposes: 600 ohms input impedance, an internal impedance transformer with 8 ohms output, a rotary switch that could well be used to redirect the output to a stereo jack (to be added) for headphones. Finally, there were enough room to add a volume control.
In fact, the R-326 does not offer a real AF gain control on its front panel. Rather, the output audio level can be controlled by acting on the RF gain control. In practice, it is expected that the audio level be controlled externally, on the loudspeaker.
The LS-166/U detailed information can be found here: LS-166/U
This is the original schematics of the unit:
This is how I have modified it (I hope it is readable):
I removed the original cable (terminated by the U-77/U connector) and replaced it with a robust bipolar cable terminated by two very simple banana plugs, suitable for the R-326 audio output socket.
Then I re-wired the internal connection to adapt for the addition of a 100 ohms wire potentiometer and a stereo 6.3 mm jack.
NOTE: after first period of usage, I preferred to re-wire the volume control as a voltage divider, in parallel with the secondary of the impedance transformer. The original series connection did not allow to completely silent the audio output.
This is a short video showing the unit while working connected to the R-326 receiver.
Here below a brief photo story of my modifications.
The re-wired internal connections
The added audio level control and headphones jack
The original switch now selects speaker or headphhones
The Mivar R46 is a transistor-based radio receiver from early '70s. Mivar (Milano Vichi Apparecchi Radio) was an Italian firm founded by Mr. Carlo Vichi in 1945 (initially the brand was simply VAR). The company produced TV sets and radios until 2014, when it became clear that it was no longer possible to fight (in terms of cost reduction and R&D investments) against competitors from abroad that were too bigger than Mivar.
More about Mivar history at following link: Mivar - Wikipedia
The R46 t is a 60 cm long radio receiver with LW, MW, SW and FM bands. It has volume (AF gain) and tone controls. The tuning dial is wide and nicely backlighted by four 6 V, 50 mA (0,3 W) lamps behind it. A big tuning knob and the band switching push-buttons complete the set of controls on the front panel, which also features a very nice signal level meter near the top right corner, just above the tuning knob. The push-buttons include the "Fono" mode switch, which converts the unit in simply an audio amplifier. The input connector for this mode is on the rear of the radio, in the form of a DIN 5-pins plug which also hosts the output connection for a tape recorder.
Front panel of R46 (left side)
Front panel of R46 (right side)
Other connections on the back panel are: two antenna connections, one for the SW band and one for the FM band (LW and MW use the internal ferrite antenna) and a mains voltage selector (with options for 220VAC or 125VAC).
Externally, this old radio looks simple and solid, with a very clean and quite elegant design.
The same simplicity and cleanliness can be found once you start to dismount the receiver: three screws on the rear side to remove the back panel, four screws on the bottom to free the chassis from the enclosure, four screws to remove the loudspeaker from inside the unit. Pull out the three knobs from the front panel and you can easily extract the chassis together with the loudspeaker. Very fast and safe.
Rear panel of R46 (left side)
Rear panel of R46 (right side)
The loudspeaker
Loudspeaker removed
Also the tuning dial (which is made by glass) can be easily unlocked from the chassis.
The tuning dial of R46
Tuning dial removed
Two of the tuning dial lamps
The electronics as well looks well designed, with a very rational and clear layout of different sub-assemblies: the RF (antenna and tuning) section, the IF amplifiers, the power supply and AF amplifier. Each of the main sub-units is individually shielded and there is plenty of room to operate for repair or re-alignment.
The electronics of R46
The ferrite rod of the LW/MW antenna
The tuning capacitor, antenna and RF sections.
On the right side, the DIN connector for audio input (FONO) and output (TAPE)
The IF section on the left of the power supply and AF amplifier
Mains voltage selector on the power supply section. On the left, the IF subassembly
The bottom side of the power supply and AF amplifier section
The bottom side of the RF/IF section
The ferrite rod wich acts as the LW and MW antenna is notably long, which ensure good sensitivity. The aerial and oscillator coils are wound over plastic supports that can be easily moved along the rod to find the better position during RF alignment operations.
My unit came in good working order (apart from the probable need of a better alignment) so I decided to spend time only for some internal and external cleaning.
First, I had noticed that the volume potentiometer was soldered "quick and dirty", probably because of a replacement after a fault of the original device. So I started with trying to improve that point.
Before and after
Then I had to improve the functionality of the band switch push-bottons, which showed an intermittent behaviour (quite tipical for old radios), especially on the MW band. I used a spray contact cleaner and repeatedly operated the switches until they started to work fairly well.
For general cleaning of chassis and PCBs I used 99,9% isopropyl alcohol. I applied it with the help of a paintbrush and a toothbrush. I used compressed air both before (to remove dust) and after the cleaning (to remove any excess of alcohol).
There was a small piece of plastic that went detached from the chassis. I restored it in place with a drop of cyanoacrylate adhesive.
The tuning dial and the knobs what cleaned up with some warm water and just a bit of soap.
Finally, the wooden enclosure was treated with a specific oil, by first applying it with a paintbrush and then by polishing up the surface with a soft piece of cloth.
Here below you can see the results, which are pretty satisfying to me:
This is the second part of my description of the restoration work I did on a Geloso G.256 vintage tape recorder. Please find part one at following link:
In part two, I first did a gentle cleanup of the plastic enclosure of the unit, using some drops of soap in warm water, a paintbrush and a toothbrush.
Then it was time to look after the electronics. First of all, I measured voltages on socket pins of the two main tubes, the 12AX7 and the EL95. I found that all values were more or less as specified in the service manual. I decided to order two new tubes (just to make sure the unit was equipped with good ones), then I thought I could test the behavior of the unit with an old tape reel that had come with it.
The short video below shows the result (not that bad, I thought).
By the way, the song that the unit plays in the video was recorded from an old Italian TV show named "Canzonissima", in 1972.
When new tubes arrived, I put them into the unit and made a new test with the same tape. Frankly speaking, I didn't notice any special improvements. Anyway... well, now it was equipped with new tubes and it was time to reassemble the plastic enclosure and to complete my simple restoration attempt.
The replacement tubes: a EL95 and a ECC83 (12AX7)
The video below shows the final result. At the end of the day, I was satisfied with it. It had been a pleasure to play a bit with this little piece of history of consumer electronics in Italy.
