Sunday, June 10, 2012

Telefunken Match

It might seem odd that I'd go out of my way to  purchase a broadcast band AM receiver, given that I won't allow a factory-made ham rig into my shack. What's more, I'm not the "collecting type" and I don't listen to broadcast band AM radio.

Nevertheless, I've long admired the design of this particular "transistor radio," and when one was found going "für einen Apfel und ein Ei" I found it impossible to resist.

The Telefunken Match was an early project by the well-know German/Italian designer, Richard Sapper.

My Telefunken Match arrived in the lower half of its original box packing, along with the instruction manual. A corroded battery holder coupled with a spot on the leather case was obviously the result of the radio having been stored away with the batteries installed at some point in time (notice the spot on the instruction manual as well). Otherwise, the radio is in nearly perfect aesthetic condition.

Applying a current-limited 6Vdc supply to the radio only produced a soft hiss in the loudspeaker. A schematic diagram pasted to the inside of the radio (complete with proper node operating potentials) made it an easy task to pin-point the problem. Here's a scan of the schematic.

The 2nd IF amplifier transistor was found to be shorted from base to the emitter; a Telefunken AF172. I happened to have a spare AF138 device on-hand, which has similar specifications. The radio came to life once the replacement transistor was installed. The alignment was found to be only slightly off. The sensitivity is excellent, although the noise level is somewhat higher than what one would normally expect from this type of radio. Although I haven't yet gotten around to isolating this issue, I suspect that at least one of the transistors has become noisy and needs to be replaced.

My receiver tunes from 495 to 1870kHz (the slide-rule dial calibration is spot-on). Using only the internal ferrite antenna I had no problem copying W1AW's evening code practice session on 160m (1802.5kHz). My bench signal generator provided the beat-frequency-oscillator with no connection needed to the radio. Broadcast band AM stations filled the dial, roughly a third of which were French language stations transmitting from nearby Quebec.

Here is a scan of the original (October 1966) instruction manual.


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