Philips B1X02A/70

The radio is sold for € 75.00 on January 7th, 2015

1960

Condition and performance:

	Cabinet:	80%
	Reception AM:	80%
	Reception FM:	70%
	Sound Quality AM:	60%
	Sound Quality FM:	60%
	Sound Quality P.U.:	60%

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:	Yes, MW plate antenna
	Build in Ferrite or Window Antenna:	No
	Separate AM/FM tuning:	No

Technical Specifications (Partially measured):

	Tubes:	ECC85, ECH81, EF89, UABC80, UL84, UY85.
	Wave Bands:	MW, FM from 87.5 - 100 MHz
	Intermediate Frequencies (IF):	452 kHz, 10.7 MHz
	Loudspeaker:	AD 1400 W
	Resonance Frequency Fs:	?
	Frequency Range Power Amplifier:	?
	RMS Output Power at 5 Ohms:	No
	Cabinet:	Bake-lite, cream white painted.
	Dimensions:	29.5 x 15.5 x 14 cm
	Mains Power Voltages:	110, 127, 220 Volts~
	Mains Power Consumption	45 Watts
	Retail Price	?

Description:

The Philips B1X02A radio is in fact the same as the Philips B1X92A. See the description of the Philips B1X92A.

Repairs:

Before making any repairs and measurement, a safety transformer is used as well as a series bulb of 220V 60W is used. After a few minutes, I found out there is no sound at all.

3 Paper/tar capacitors of 4700 pF at the P.U. entrance are replaced by 4700 pF 1000V.
Reason: Electrical safety.
Decoupling capacitor C40 of 10 µF is removed.
Reason: Reduction in amplification gain. The volume control works now more gradually. The power supply hum has also decreased. The sound quality is also slightly better now.
Cathode resistor UL84, R19 of 180R 3W is replaced by 220R 3W.
Reason: Increasing the lifetime of the UL84 and preventing positive grid voltage of the UL84. Don't worry about the less ideal class-A setting. In most cases, even the audio output power increases a little bit.
C41 of 10 nF is replaced by a series network of 4K7 3W and 2200 pF 1500V.
Reason: More flat impedance load, more stable operation of the power amplifier and extending the high frequency range.
Power amplifier is modified, regarding the the schematic diagram below.

The blue components are the added components for improved bass reproduction.
The red components are the modified components.

Performance:

After repairing this radio, the reception of the broadcast stations on FM and MW is quite well.
After modification, the sound quality has improved a lot. More pleasant, less mid-highs, more bass and more top high frequencies.

Disclaimer:

The build in power transformer is only meant for the heater voltage of 6.3V~ and the different primary voltages. The high voltage supply is directly taken from the mains power, which means the radio chassis carries the 220 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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