Grundig 1012GW

1952

Condition and performance:

	Cabinet:	80%
	Reception AM:	90%
	Reception FM:	70%
	Sound Quality AM:	80%
	Sound Quality FM:	80%
	Sound Quality P.U.:	80%

Features:

	P.U. Entrance:	Yes
	Tape Recorder Entrance:	No
	Extra Loudspeaker Output:	No
	Loudness:	Yes, only on bass
	Treble Control:	Yes
	Bass Control:	No
	Tone Register Switches:	No
	AM Bandwidth Switch or Control:	No
	Tuning Indicator:	No
	Build-in Antenna:	Yes, FM Netzantenne
	Build in Ferrite or Window Antenna:	No
	Separate AM/FM tuning:	No

Technical Specifications (Partially measured):

	Tubes:	UC92, UCH81, UF41, UABC80, UL41
	Wave Bands:	MW, FM from 87.5 - 100 MHz
	Intermediate Frequencies (IF):	468 kHz, 10.7 MHz
	Loudspeaker:	Grundig, Oval type, 15 x 22 cm, bake-lite loudspeaker chassis
	Resonance Frequency Fs:	?
	Frequency Range Power Amplifier:	?
	RMS Output Power at 5 Ohms:	?
	Cabinet:	Wood, brown lacquered.
	Dimensions:	48 x 31 x 22 cm
	Mains Power Voltages:	110, 125, 220, 240 Volts AC/DC
	Mains Power Consumption	45 Watts
	Retail Price	DM 236,00

Description:

The Grundig 1012GW is a smaller radio, which can be operated at mains voltages of 110-240 Volts, AC or DC.
It is a cheaper radio, but even this "low-class" radio have a very good performance.

Repairs:

First inspection shows, the dropper resistor is fully defective and burn out. The main cause is, the Selenium rectifier has a short cut.
Before making further measurements, the selenium rectifier is replaced by a BY127 diode and a series resistor of 330 Ohms 9 Watts. The radio is then ready to operate at 233 Volt AC/DC, which is suitable for the today's mains power voltage.
After connecting a series lamp of 220V 60W, the grid of the UL41 became a positive voltage, so the coupling capacitor C45 of 50 nF is replaced by 47 nF 1000 Volt.
Finally all the 20 ERO capacitors are replaced by new ERO capacitors, and this improved the performance to the factory specifications, like a new radio.
Below you find all the replaced components with their reason and which effect it has.

V45 of 50 nF is replaces by 47 nF 1000 Volt.
Reason: Leakage and positive grid voltage. Usually this ruins the EL41, output transformer and power supply.
Anode capacitor C50 of the UL 41 of 5000 pF is replaces by 4700 pF 1000 Volts.
Reason: Increased value results in a darker sound or less reproduction of the high frequencies. This capacitor is used for the MW band to reduced the noise and 9 kHz whistling tone of the nearby AM broadcast stations.
Anode capacitor C51 of the UL 41 of 2000 pF is replaces by 2200 pF 1500 Volts.
Reason: Increased value results in a darker sound or less reproduction of the high frequencies. Another part also is when this capacitor has a leakage, it runes also the UL41, output transformer as well as the power supply.
C46 of 1000 pF is replaced by 1000 pF 1000 Volt.
Reason: This capacitor is placed in the negative feedback circuit and is responsible to increase the higher frequencies of the audio reproduction. It results finally in a nice bright sound.
C47 of 1500 pF is replaced by 1500 pF 630 Volts.
Reason: this capacitor is placed in the feedback circuit and is for the tone control. This capacitor is also responsible to increase the bass frequencies for a more full sound.
A 22 nF 630 Volt capacitor is added to the tone control. It is connected to the anode of the UABC80 and center tap of the potentiometer. The left tag is connected to ground.
Reason: Better tone control.
C41 of 10 nF is replaced by 10 nF 630 Volt.
Reason: Leakage, which results in no negative voltage anymore. The anode voltage of the UABC80 drops too much, which results in distortion and low audio power output.
C59 of 10 nF is replaced by 10 nF 630 Volt.
Reason: Extra HF decoupling of the power supply.
C44 of 50 nF is replaced by 47 nF 630 Volt.
Reason: Hum of the pre-amp stage of the UABC80 has now reduced a lot.
Resistor R20 of 100K is replaced by 100K 3W.
Reason: Noise and crackling sound.
FM ratio detector capacitor C40 of 4 µF is replaced by 4.7 µF 63 Volt.
Reason: Distortion by FM reception.
C43 of 5000 pF is replaced by 4700 pF 1000 Volt.
Reason: Safety reason for the P.U. entrance.
C43 of 5000 pF is replaced by 4700 pF 1000 Volt.
Reason: Preventing AM/FM negative voltage from the detector to the potentiometer. It cuts off also the lower frequencies which the loudspeaker can't reproduce and reduces therefore also the distortion in the low frequencies.
C20 and C30 of 25 nF are replaced by 22 nF 630 Volt.
These capacitors are HF decoupling capacitors on the cathode of the UCH81 and UF41. Not critical, but the IF gain improves a little bit.
C19 and C32 of 25 nF are replaced by 22 nF 630 Volt.
Reason: These are screen resistors of the UCH81 and UF41. Due to leakage, the voltage drops and the IF gain is less, which results in less reception sensitivity.
C25 of 25 nF is replaced by 22 nF 630 Volt.
Reason: Decoupling capacitor of the IF and anode to the UF41. It prevents also burning and/or destroying of R39 of 2K.
C16 of 100 nF is replaced by 47 nF 630 Volt. R10 of 3M is replaced by 1M 1 Watt.
Reason: Faster end better Automatic Gain Control (AGC) of the MW band. Strong broadcast signals tends less to overload and the amount of soudn is almost the same as from weaker broadcast stations.
C7 of 5000 pF is replaced by 4700 pF 1000 Volt for safety reasons.
C2 of 1000 pF is replaced by 1000 pF 1000 Volt for safety reasons.
C37 of 500 pF is replaced by 500 pF 630 Volt.
Reason: Leakage. Negative Am detection voltage is now improved.
Decoupling chatode capacitor C49 of the UL41 of 50 µF is deleted.
Reason: Gain reduction due to local current feedback. Today's broadcast stations have a stronger audio signal. This results now in a better loudness control, better tone control and less power supply hum. The power amplifier operates also more stable.

Performance after repairs:

After these extensive repairs, the Grundig 1012GW meet now almost the factory specifications with some extra improvements.
The power supply is only suitable now for the current mains power voltage of 230V~.
The reception on both FM and MW is very good.
The sound quality is also good, which makes Grundig famous, even of the small radios.

Disclaimer:

This radio is directly supplied from the mains power. The high voltage supply is directly taken from the mains power, which means the radio chassis carries the 230 Volt~ mains voltage, which is very dangerous. Before making any repairs on the radio or playing the radio without the back plate, use a safety transformer with separate windings. The insulation of the windings must withstand at least 4000 Volts AC as well as a low leakage current of 0.5 mA~ or less.

Home
Back to Picture Gallery 2
Contact Kees van Dijke
Download the schematic diagram.