Philips B1X92A/69

1959

Condition and performance:

	Cabinet:	80%
	Reception AM:	80%
	Reception FM:	70%
	Sound Quality AM:	50%
	Sound Quality FM:	50%
	Sound Quality P.U.:	50%

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:	?
	Cabinet:	Bake-lite, dark brown.
	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 B1X92A looks almost the same as the Philips B0X15U, so it is a bigger brother. The main difference is the addition of the FM wave band and a tone control switch. Another part is also the different tube line up, a mixed version of the E-types and U-types tubes.
Both FM and MW tuners have inductive tuning, so there is no ferrite antenna build in for MW reception.
The power transformer is an auto transformer without separate windings. These transformers are cheaper and smaller, but the drawback is, the radio chassis carries the mains voltage which is dangerous when playing the radio without the back plate.
The P.U. entrance is decoupled by 3 capacitors of 4700 pF. Because the ground tag is also connected with a 4700 pF capacitor, you would expect hum, but in this case, it is an impedance balanced input with a ground lift. When a record player is correctly connected, there is no hum.
The tone control and FM/MW switches are shift type switches. You have to pull it up or push it down.

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.

Cabinet is cleaned inside from dust.
A small tear in the cabinet is fixed with a small amount of super glue and the tear is hardly visible now.
MW plate antenna is glued.
Fuse Z4 of 63mA has blown out.
Reason: C41 of 10 nF 400V has a shortcut. This is a famous Philips polyester capacitor which have even today the best quality, but even these capacitors can become defective. C41 of 10 nf 400V is replaced by 10 nF 1000V. When Z4 is open, the screen of the UL84 act as an anode, withdraw too much current and become then defective soon. You see also a bright orange glowing spiral which is very suspect.
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.

The UL84 shows blackened traces on the glass due to overload, but the UL84 is OK and there is no positive grid voltage.

Performance:

After repairing this radio, the reception of the broadcast stations on FM and MW is quite well.
The sound quality is terrible. No top high audio frequencies, too much in the mid-highs and no bass. Finally the type of sound is very thin and aggressive.
A similar model radio, the Philips B1X02A will also be repaired and modified to improve the sound quality.

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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