Gerard's Tesla 3002

138
Item nr.

Tesla 3002 Minor Duo

Compact tube portable with AC adapter.

**Data for Tesla 3002**
Production	Czechoslovakia, 1958.
Bands	SV (185-577m), KV (24-52m)..
Tubes	1H33 (converter), 1F33 (IF stage) 1AF33 (AF stage), 1L33 (output tube)..
Cabinet	Cardboard and bakelite. Size 24x14x7 cm (ex adapter). Weight 1.8 kg with batt..
Power	AC adapter or batteries 67.5 and 1.5V.
Documents	Schema.

The Design

The Tesla Minor Duo technically ressembles Western radios like the later Philips L2X80B, although it does not reach the degree of miniaturization of the Japanese Highness. It's most interesting feature is the AC power supply housed in a separate adapter, which also serves as a stand for the radio. This reduces the weight when the radio is in portable use, while avoiding the battery cost when the radio is used in the house. Additionally, the AC adapter can be used to charge the batteries. Of course, dry batteries cannot really be charged, but the adapter sends a small reversed current through the batteries. This operation removes hydrgen bubbles forming in the batteries, which extends their life span if repeated from time to time.

The power switch only cuts off the filament current, leaving the B+ battery connected! The radio is supposed not to draw any current from this battery when the filaments are cold.

Obtained	11/1999 from Bazar Prague.
Condition	8.
Disposed	Sold 1/2004.

This Object

The Czech line of battery tubes have 25mA filaments, like the Western tubes used at the time, but interestingly the output tube takes the same amount of current. Thus, overall draw from the filament cell should be 100mA.

Unfortunately, these Czech tubes are hard to find here in the Netherlands, so I had to replace the 1H33, 1F33, and 1L33 by DK91, DF91, and DL92. These tubes are pin-compatible (the output tube automatically comes into saving mode because only one half of its filament is heated.) For battery economy, replacement by the D*96 tubes would be preferrable, as these take only 25mA each. The band switch was defective with the contacts unreachable, a previous owner had solder-connected all MW coils, cutting out the SW coils. I decided to leave this. The radio was badly aligned: this could be expected as I found some of the coils loose in the cabinet and had to glue and solder them in place. I didn't succeed to align it in the usual way, but then used a dipmeter to see the resonance frequency of each of the individual coils.

The mains power supply is defective: the secondary coil providing the B+ is interrupted. Anybody having a spare lying around collecting dust?

Part of Gerard's Radio Corner.
Generated by SiteBuilder on 6/9/2025 by Gerard