Grundig 87a

1960

Condition and performance:

	Cabinet:	50%
	Reception AM:	90%
	Reception FM:	80%
	Sound Quality AM:	75%
	Sound Quality FM:	75%

Features:

	P.U. Entrance:	No
	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:	Yes
	Separate AM/FM tuning:	No

Technical Specifications (Partially measured):

	Tubes:	ECC85, EBF89, ECL86
	Wave Bands:	MW, FM from 87.5 - 100 MHz
	Intermediate Frequencies (IF):	468 kHz, 10.7 MHz
	Loudspeaker:	Grundig, Oval type, 10 x 15 cm
	Resonance Frequency Fs:	?
	Frequency Range Power Amplifier:	?
	RMS Output Power at 5 Ohms:	?
	Cabinet:	Wood, brown lacquered.
	Dimensions:	33.5 x 21 x 14 cm
	Mains Power Voltages:	220 Volts~
	Mains Power Consumption	35 Watts
	Retail Price	DM 139,00

Description:

The Grundig 87a is a small and cheap radio with a surprising good performance. There are no features, like an extra loudspeaker output and a P.U. entrance.
There are only 3 tubes build in. Normally you would expect an extra ECH81 tube and eventually a FM detector tube, like the EAA91. However, this is a complete radio set with a good reception sensitivity and a good sound quality.
The AM oscillator is done by the ECC85. The AM mixer is also done by the other half of the ECC85 which works as an additional IF mixer, which is common in transistor radio's. Furthermore there are there are the usual IF stages for AM at 468 kHz as well as normal AM detection by the EBF89, so the sensitivity of broadcast stations is the same as other tube radio's.
The FM part is different. There is one IF coil set less as usual. To compensate the loss of the IF amplification, the IF circuit is based on a reflex (Audion) circuit on the 10.7 MHz IF stage and can be adjusted with C37 of 3 pF. In this case it is possible to get the same reception sensitivity as the usual tube radios.
The FM detection is done by 2 crystal diodes RL233 and is a normal ration detector.

Repairs:

In the past, the previous engineer has replaced the coupling capacitor of the ECL86. This ensures at least a basically safe operation, but to improve the performance and safety, other components are also replaced. All the ERO capacitors are replaced by modern new ERO capacitors for optimal performance and safety. Below there are exceptions of some replaced components with their reasons.

Selenium rectifier B250C85 and resistor R32 of 82R are replace by 1N5408 and 150R 5W.
Reason: These components shows traces of overheating. After replacing these components, the high voltage increased from 210V DC to 250 DC which is and ideal value.
Decoupling cathode capacitor of the ECL86 C41 of 25 µF 12V is deleted.
Reason: Too much amplification gain with today's stronger audio signals from the broadcast station. The loudness function works also better which results in less distortion at a loud volume setting.
C7 of 470 pF is replaced by 150 pF.
Reason: Better highest audio frequency reproduction, more Hi-fi alike then.

Performance:

After repairing this radio, it is now fully operational and the electrical safety is also optimal now. The total performance of this small and cheap radio is surprisingly good.

Disclaimer:

The build in power transformer is only meant for the heater voltage of 6.3V~. 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.

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