Item nr.

Tesla 3101B Portable

Philips remake

Data for Tesla 3101B
ProductionCzechoslovakia, 1953.
BandsLW (1000-2000m), MW (187-572m), SW (19-50m), MF is 452kHz.
Tubes1H33 (mixer), 1F33 (osc.), 1F33 (1st IF), 1F33 (2nd IF), 1AF33 (det/AF), 3L31 (output).
CabinetWood with leatherette. Size 36x23x18cm. Weight 6kg.
PowerBatt 6xD is 1.5V @ 225mA plus 90V @ 17/9 mA.
DocumentsRmorg file.

The Design

This Tesla model is 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.

Obtained6/2022 from Paul vd Mast.
Condition7; works, front damaged.

This Object

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.

Part of Gerard's Radio Corner.
Generated by SiteBuilder on 8/8/2022 by Gerard (g.tel@uu.nl)