The Philips B0X15U is the cheapest tube radio of 1961. This radio is meant
as an extra radio for the kitchen or in the bed room. Except for the antenna
input, it has no extra features at all, and only reception of the MW band is
possible.
Repairs:
Paper/tar capacitor C19 of 100 nF is replaced by an ERO capacitor of
100 nF 1000V.
Reason: This capacitor is exploded due to leakage.
Paper/tar capacitor C18 of 10 nF is replaced by 10 nF 1000V.
Reason: This capacitor is increased in value, which makes the sound too
dark.
In the past R14 of 1K of the dropper resistor has burned out. This
section is replaced by 2k2 5W resistors in parallel and is an ideal
solution for the today's 230V~ mains power voltage.
After further inspection, the radio is be able to play. When connecting
the radio to the mains power, I found out the sound quality is terrible
and very thin.
Coupling capacitor C17 of the UCL82 is 470 pF and is replaced by the
original value of 4700 pF 1000V.
Reason: This results in a RC network, where the low frequencies are cut
off. Now it sounds better.
Grid capacitor C16 of the UCL82 is 470 pF and is replaced by the
original value of 4700 pF 1000V.
Reason: Also a RC network, which cuts off the low frequencies, but less.
There was also hum and has disappeared for a great part now. Now it
sounds a bit more better.
After these repairs, the radio meets now the factory specification, but
the sound quality is still too poor, so some modifications are made for a
better sound quality and more stable operation.
R10 of 680K is replaced by 1K.
Reason: Better leakage resistor function of the UCL82. Less change the
UCL82 gets damaged in the long future.
Added screen resistor of 470R 1W for the UCL82.
Reason: More stable operation of the UCL82. It meets also the
requirements which is mentioned in the UCL82 datasheet.
Added RC network of 10K 3W and 22 µF 350V to the pre-amp of the UCL82.
Reason: Less power supply hum.
Added RRC network of 47K, 47K and 10 nF 630V.
Reason: Added bass, which results in a more full and pleasant sound. See
the schematic diagram below.
The red components are modified components.
The blue components are added components to improve the sound quality,
better stability and reducing the power supply hum.
The tube socket of the UCL82 still looks overheated and must be replaced in
the future, however, it is still useful. To prevent short cuts and
flash-overs, the top layer of the tube socket is removed.
The positive voltage on the penthode grid of the UCL82 has dropped from
+2 Volt to +0.6 Volt which is acceptable, but better is to replace the
UCL82 and tube socket.
Tubes with a cathode resistor and grid leakage resistor must usually show
0 Volts across the leakage resistor.
Performance:
The sensitivity of this radio is just sufficient, but to receive more
distant broadcast stations, it is recommended to connect an external
antenna. A piece of wire of 2 meters is sufficient.
The sound quality in its original state is very thin and harsh. There is no
loudness circuit build in as well as no negative feedback circuit. After
adding some extra components, the sound quality has improved a lot.
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 and components 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.
1961
1961
1961
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