568
Item nr.
| FOR SALE for EUR 15 Conditions |
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| Production | Czechoslovakia, 1953. |
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| Bands | LW (1000-2000m), MW (187-572m), SW (19-50m), MF is 452kHz. |
| Tubes | 1H33 (mixer), 1F33 (osc.), 1F33 (1st IF), 1F33 (2nd IF), 1AF33 (det/AF), 3L31 (output). |
| Cabinet | Wood with leatherette. Size 36x23x18cm. Weight 6kg. |
| Power | Batt 6xD is 1.5V @ 225mA plus 90V @ 17/9 mA. |
| Documents | Rmorg file. |
very similar to the Philips LX381B of 1948. It even has the same number of tubes, although they are used in a different way. Philips built a push pull output with a phase inverter and extra output tube. But Tesla has a seperate tube for oscillation and a second IF stage. In case you need the dial layout, here it is. 
Battery radio's quite often have unusual solutions in the power supply. Here we find a resistor R2 switched over the power switch, keeping the smoothing capacitor C41 unde voltage, even when the radio is switched off. I heard two reasons to do this. First, because C41 is already charged, this avoids a heay charging current when switch on. Second, keeping an electrolyt under voltage extends its life span. Whatever the reason is (this matter is discussed on page 3 of the docs of LX381B), the presence of R2 allows a sneaky current of about 50uA to deplete your plate battery in about three months when you put the set away with batteries in it. I replaced C41 by a non-electrolytic (of 5uF) and removed R2, so the battery can remain in place for years.
There is a "Saving" switch to make the plate battery last longer. In the schama it is switch P3 and it places a 4k resistor in the plate lead. The B+ then becomes about 60V and the tubes draw just around 9mA instead of the full 17mA. So, in this position (marked 1/2) the drain is just about half. But unfortunately, the energy isn't used very effectively in this case, because one third of the power goes into R5.
| Obtained | 6/2022 from Paul vd Mast. |
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| Condition | 7; works, noisy, front damaged. |
| FOR SALE | Price is 15 Euros. |
Also the inside is very much like the Philips LX381B. Except that radio has the heater batteries in the bottom of the cabinet, and consequently, the chassis a bit higher. The radio is equiped with a loop antenna, so reception is very directional.