The Philips BX210U is a small but full AM standard radio. The extra features
are the build in window antenna, also called magnetic loop antenna, for the
LW and MW bands. This antenna ensures a good reception quality without any
noise from other sources. This antenna has also directivity, which ensures a
god reception without noise.
The SW has a build in plate antenna, but is is then recommended to use an
external antenna to receive the weaker radio stations.
Other features aren't build in, but this radio makes it well as a good radio
for traveling.
Repairs:
On the picture above, you see only the most urgent parts has been replaced
to make the radio quite safely playable, but further repairs are also done
for optimal electrical safety, reliability and performance.
Paper/tar capacitor C30 of 22 nF on the output transformer is replaced
by 22 nF 1000V and is connected parallel across the primary winding of
the output transformer.
Reason: Leakage can destroy the output transformer, UL41 and UY41 as
well as the dropper resistor. Increased capacitance makes the sound also
too dark.
Paper/tar coupling capacitor C29 of 10 nF is replaced by 10 nF 630V.
Reason: Too much positive grid voltage on the UL41.
C32 of 33 nF, which is replaced in the past, is replaced by 33 nF
1000V.
Reason: More reliability.
Paper/tar capacitor C31 of 2200 pF is replaced by 4700 pF 1000V.
Reason: Leakage results in less negative grid voltage of the UBC41 and
the anode voltage of the UBC41 drops also too much.
Extra copper file is wrapped around the 4700 pF capacitor and is
grounded. The result is less hum.
Paper/tar capacitor C27 of 15 nF is replaced by 15 nF 630V.
Reason: Increased capacitance results in a bad loudness function, also
less bass and a thin sound.
Paper/tar capacitor C20 of 100 nF is replaced by 100 nF 1000V.
Reason: Leakage results in low screen voltages for the UCH42 and UF41.
Now the reception sensitivity is better.
Paper/tar capacitor C12 of 47 nF is replaced by 47 nF 1000V.
Reason: Leakage results in less AGC. Stronger broadcast stations have
then audio distortion. Increased capacitance results in a slow AGC.
Paper/tar capacitor C34 of 4700 pF is replaced by 4700 pF 1000V.
Reason: Electrical safety.
Paper/tar capacitor C3 of 1000 pF is replaced by 1000 pF 2000V.
Reason: Electrical safety. When this capacitor has too much leakage or
shortcut, the SW HF coil can be destroyed.
Resistor R8 of 22K 0.5W is replaced by 22K 1W.
Reason: Increased in value.
UBC41 gives a blue glow. The result is no sound and a quite loud hum.
Solution: A new UBC41 is placed. The old UBC41 has some rests of gas
which results in a short cut and is thrown away.
Tube socket of the UL41 is black due to overheating.
Solution: Tube socket is replaced by a 9-pins ceramic Noval socket. The
UL41 will be replaced by the UL84.
Cathode resistor R17 for the UL84 (formerly UL41) of 150R 0.5W is
replaced by 180R 3W.
Reason: Less current, less heat and increased lifetime for the UL84.
A screen resistor of 1K5 1W to the UL84 is added.
Reason: The screen and anode voltage on the UL84 is now equal.
A 10K 2W resistor and 22 µF 350V capacitor is added to the supply for
the UBC41.
Reason: Less hum.
Improved AM detection network added. See the small schematic diagram
below.
Reason: To get rid of the negative AM detection voltage on the volume
potentiometer. It didn't help much, so the volume potentiometer must be
renewed.
The potentiometer of 50K+450K is replaced by 0M4+1M6. The loudness
network is changed to 100K and 3300 pF.
Reason: Too much cracks on the potentiometer and often no or
disappearing sound.
The red colored components are the added components for a better AM
detection and to get rid of the negative detection voltage on the
potentiometer.
The blue colored components are the modified components.
The UL84 is similar to the UL41 and is a good replacement.
Volume potentiometers are hard to get for this old radios, but changing
the taper, loudness circuit and using the improved AM detection circuit
makes any potentiometer taper useful. The sound quality and loudness
function are almost the same then and in a few cases even improvement.
Performance:
After a lot of this electrical repairs, the radio plays now very well. It is
worth to make a full electrical repair, even if the components are still
useful at less critical and even faulty safe places.
The reception quality and sensitivity is good.
The sound quality is also quite well and nice.
The tone control switch makes the sound finally too dark and I find it less
useful.
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 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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