On this site:

Erres KY552 (1955)

The Erres KY552 is a portable radio from 1955. It comes in an elegant reddish brown bakelite case that sports a few unique design features. It can run from batteries or mains and offers good reception and sound.

    The case is composed of two identical shells

The case is composed of two identical shells

The KY552 is one of the rare portable valve radio models by Erres. Its designers have really done their best to make a radio that looks special. The case is composed of two identical halves that fit together like a clam shell. The radio is perfectly symmetrical: it does not appear to have a front and back, just two fronts, each with a tuning dial. The shape of the case with the big handle on top sends the message: this is a portable radio. The overall shape is not unlike nowadays' "ghetto blasters". The tapering cross bars over the speaker grille resemble a star, reminding us this radio is from the jet age.

The 2 IF stages make this radio quite a sensitive radio, despite the fact that it uses a built-in frame antenna. On all three wave bands it can receive ample stations.

The valves used are 7-pin miniature battery types, with 25 mA filament The filament voltages are 1,4 V per valve, except for the DL96 that has a double filament.

The valves add up to 8,4 V, to be supplied by 6 type "C" dry cells. The radio also needs a 90 V anode battery.

I saw the radio on the advertisement section of the Dutch Forum on Old Radios. It was sold as slightly damaged because it had a hole in the bottom. When I collected the radio, the hole turned out to be a missing piece of the bottom broken off. The hole and some cracks in the case are evidence that the radio must have had a fall. The radio was also quite dirty, it was housing several species of insects. The previous owner had already cleaned one half, but the radio still could do with a good scrub.

    The inside after repair.

The inside after repair.

To be able to to clean the case, I took the chassis out and removed the speaker grilles. I first cleaned the chassis and then analysed the circuits. The safety interlock, intended to disconnect the radio from mains when the case is opened, had been bypassed, apparently because the pin was missing that should push and close the interlock. Such a safety switch is sensible because this radio has no mains transformer, so when running from mains, it is an AC/DC radio. One conductor of the mains cord (preferably Neutral) is directly connected to the chassis. The Live conductor is connected to a single phase selenium rectifier, that charges a buffer capacitor to about 250 V (when connected to 230 V AC mains). The excess voltage above 90 V is dropped over a dropper resistor, that has several taps for different mains voltages. A second dropper resistor is placed in series with the filaments. The valves only have a filament current of 25 mA, so the power consumption is modest, even for a battery valve radio.

These small directly heated valves heat up very quickly, resulting in practically no turn-on delay. When I tried the radio, it almost immediately produced a hum. For the rest it remained silent, though. After some fiddling, I could get a few stations on LW, but nothing on SW or MW. Still later on, I could hear some stations on SW, and still later MW came to life.

After trying a few times, I got the impression that the waveband switch was dirty. After I had cleaned the waveband switch, the radio seemed to work better. But the next day the real cause of its unreliable behaviour came to light. One of the wires of the oscillator coils had not been soldered properly and did not make a reliable connection. I also checked the coupling capacitor to the output valve. That one turned out to be very leaky. After replacement of this capacitor, the output valve worked a wee bit better. Then I noticed the filament voltage was a bit too low. Probably because the internal resistance of the rectifier has increased. Therefore, I adjusted the series resistor in the filament chain.

To finish things, I polished the bakelite using car polish and cleaned the two dial windows (plastic, probably acrylic).

After all this, the radio played fine. I listened to it for a while, to be disturbed by a faint hissing sound. I ran to pull the plug and opened the radio. Not a leaky electrolytic, as I had feared. The mains RF filter capacitor had run hot. I should have anticipated this, because it is a paper capacitor encased in tar, the type that gets leaky after a while and runs hot when continuously connected to HV AC. After replacement of this capacitor, the radio was ok. I am using it every now and then and every time again I'm pleased by its good reception and pleasant sound.

Copyright © 2006 by Onno's E-page         published 2006-02-26, last updated 2008-10-04