Blaupunkt Standard Super GW

1947

Condition and performance:

	Cabinet:	50%
	Reception AM:	100%
	Sound Quality AM:	90%
	Sound Quality P.U.:	90%

Features:

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

Technical Specifications (Partially measured):

	Tubes:	UCH81, UBF80, UCL82, UL41
	Wave Bands:	LW, MW, SW from 16 - 50 meters
	Intermediate Frequencies (IF):	468 kHz
	Loudspeaker:	AD 3700AM
	Resonance Frequency Fs:	63 Hz
	Frequency Range Power Amplifier:	15 - 20,000 Hz
	RMS Output Power at 800 Ohms:	3 Watts
	Cabinet:	Bake-lite, dark brown.
	Dimensions:	37 x 25 x 22 cm
	Mains Power Voltages:	230 Volts~
	Mains Power Consumption	?
	Retail Price	?

Description:

The radio came in as a wreckage. No back plate, no loudspeaker, no tubes, no power cable, no output transformer, a broken cabinet and broken tube sockets.
However, the most important parts, like the HF parts, IF section and knobs are still there. Most components are also removed, so the radio will be build from almost scratch and this gives the opportunity to make a high quality AM radio with more modern tubes, but with the same tube technology of the past. The volume potentiometer of 1M is replaced in the pas by 500K log with a switch and is in very good condition.
In the original state, the tubes are the UCH5, UCH5, UBL1 and UY3. These tubes can be replaced by the UCH81, UBF80, UCL82 and UL41. The UY3 is replaced by a bridge rectifier 4x 1N5408. The UL41 is added, because no output transformer will be used.
The power amplifier will be made by an OTL 800 Ohms amplifier and the radio section will be made as show as in the datasheets of the UCH81, UBF80 and UAA91.

Repairs:

The power amplifier and power supply is build from scratch. The inspiration of the power amplifier is the same as in the schematic diagram of the Philips 23TX371A television set. See the schematic diagram below.

Schematic diagram of the power amplifier and power supply.

Since the volume potentiometer has no loudness function, an extra RCC network (blue) is added to relatively increase the reproduction of the bass frequencies, which results then in a more full and deep bass sound.

The heater section has a serial resistor of 820 Ohms 10 Watts. A separation diode 1N5408 is added, so the heaters of the tubes and the dial scale lamp of 19V 0.1A with the 820 Ohms series resistor have only to handle 230 Veff.
Parallel with the 19V 0.1A lamp, 2 zener diodes of 24V 1.3W in anti series are connected, to prevent the high inrush voltage of the dial lamp, which increases then the life time of the dial scale lamp.
The HF and IF section is taken from the datasheets of the UCH81 and UBF80. Other parts are the same as in the original schematic diagram.
The AM detection is the same as from the datasheet of the UAA91.

Further repairs are also done.

The tears in the cabinet are glue with super glue. Because the cabinet is a bit malformed, the result isn't invisible, but acceptable.
4 HF trimmer capacitors are renewed by 3 - 40 pF types.
Reason: The silver layer has vanished which makes it then impossible to get an optimal sensitivity and bandwidth.
IF part is re-aligned for optimal sensitivity and bandwidth.

Performance:

After rebuilding this radio set, the sensitivity of the broadcast stations is excellent, due to the application of brand new tubes.
The sound quality is very well, due to the OTL power amplifier. Deep bass and a nice bright sound when connecting a Philips A5X83A tuner to the P.U. entrance.

Disclaimer and warnings:

Since the radio has no power transformer, as well as the application of a bridge rectifier which is directyl connected to the 230V~ mains voltage, the chassis carries ALWAYS a voltage of 115V DC. This is dangerous. In case you want to connect a record player of a FM tuner, be sure it is fully isolated and not grounded. Use as antenna a simple wire antenna on the FM tuner.

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Download the schematic diagram (original).