Terta T331               

                   ( TelefongyŠr )             

Terta T 331
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    EM4 modify    






TERTA ( TelefongyŠr )







Frequency range

Long Waves 715-2000 m.(150 - 420 Kc), Medium Waves 185 Ė 570 m.(525 - 1580 Kc), Short Waves 16 - 50 m.(6 - 20 Mc)


ECH21 - ECH21 - EBL21 - AZ1- EM4

Intermediate frequency 473,6 Kc

Power supply

110 / 120 / 150 / 220 V. a.c.

Measure of the case

51,8 cm wide; 36,5 cm tall; 26,5 cm deep.

Overall dimensions

53 cm wide; 37,5 cm tall; 26,5 cm deep.


10 Kg


TERTA T331 itís a simple but very good superheterodyne set, the electric diagram is similar and is derived from Orion 331 model, furthermore the chassis is the same of Orion 331.
This set works very well and can receive several stations on medium, long and short waves.
The rotating switch band is operated by the knob in the right side of the cabinet.

The left knob operates the power switch / volume control and the right knob is for the tuning. The central knob operates the tone control.  


The most common problems and how to solve it:


The main problem this radios have, are the contacts of the rotating band switch.
As the time goes by, they oxidize and this causes the malfunction of the set.
That isnít a big problem, you only have to clean the contacts of the rotating band switch and the radio will work good.
To make this work, you have to remove the band knob and the black bakelite cover of the rotating switch. Now you have to clean the contacts with a spray contact lubricant, then rotate many times the switch to improve the cleaning.
Important: use lubricant spray, NO DEGREASER SPRAY!


The tuning indicator (Magic Eye) brightness is low:

Usually, in these old sets, the tuning indicator is not in good conditions or even is completely exhausted.

If it is totally exhausted, there is nothing to be done; in case the brightness is still present but very poor, you can recourse to a stratagem to increase it.

Remove the wire that is connected to the anode of the valve, connect the same anode to a voltage supply generated separately by a diode and two capacitors, as you can see in the diagram showed on the left of the page. By making this, you will obtain an anodic voltage of 50 V more of the normal voltage.

In this mode, you will obtain an accettable brightness of the magic eye.

To have more brightness, someone supplies these valves with voltage doublers, but in this mode, the applied voltage is too high and the valve will be exhausted in a short time. By using my system you will obtain a decent brightness and the valve can work for many hours.