406
Item nr.


Philips D2243/00 Portable

Four band portable


Data for Philips D2243/00
ProductionMalaysia, 1985.
Bands MW (525-1606kHz), SW1 (2.3-7.3MHz), SW2 (9.5-21.75MHz), FM (88-108MHz); IF 468kHz, 10.7MHz. Person typing dial was sleeping.
Semi-
conductors
TDA1220, TBA820M, 2 transistors, 4 diodes.
CabinetPlastic. Size 25.5x16x7.5cm.
PowerAC 230V (1,0W) or Batt 4xC.
Documentsschema D2214.

The Design

This modern radio contains very few parts. Except for two transistors in the FM front end, the entire RF strip is packed in the TDA1220 IC and the entire LF amplifier in the TBA820. Sound quality is most restricted by the use of a cheap 3 inch speaker.

The D2243 is a close copy of the D2214. The latter has the same shape, as can be seen on this advertisement, and almost the same schematic. Difference is that it has the Tropical band (running from 2.3 to 7.3 Mc, including the 120m, 90m, 75m, and 60m broadcast bands), in stead of the Long Wave band (not used in the tropics). In the time the radio was built, this Tropical band was already a bit in decline. The dial designer made a good job of changing the frequency figures, but he forgot to write MegaHertz instead of kiloHertz. So it looks like we have a nice misprinted dial here.

The TDA1220B IC has date code 98518 so was produced in week 18 of 1985. The TBA820M has date code 88505 so was produced in week 5 of 1985. The radio has production code 529 (sticker in battery compartiment) so is from week 29 of 1985.


Obtained6/2015 from Activiteitenmarkt, sn=RZ14047.
Condition8.

This Object

To pull the chassis, removal of the front knobs isn't necessary. You must unscrew the four screws in the back (one in the battery compartment) and the back can be taken away, including the power transformer. Then you can do some measurements and small mods, but to see the other side of the PCB you must unscrew the two screws near the top edge of the PCB. Then you can take out the PCB, and the dial drive chord and volume pot will remain in the cabinet! This picture shows that there was no constructional need to keep the speaker so small.

I had to pull the chassis several times in November 2016, when we found out that the radio produced a barely audible 100Hz hum. This was only noticeable under "bedside" conditions: lying silently in bed, your ear almost touching the speaker and listening at absolutely minimal volume. I opened the set, and, following a discussion on the Transistor Forum, tested almost all defects known to cause hum in the History of Mankind.

The three 470uF elco's are primarily responsible for suppressing power supply ripple and I checked all three of them. That means unsoldering, measuring the capacity, temporary replacement by a new capacitor, putting the old component back, and placing an extra capacitor over the contacts. None of this made any effect, the measured capacity was over 500uF of each (it isn't uncommon for elco's to measure a bit higher than the nominal value), which gives a triply secure indication that these components are OK. I got the suggestion that the hum be caused by magnetic fields of the power transformer, but moving the transformer relative to print and speaker made no effect, refuting this theory. The TBA820 chip has a special pin dedicated to hum suppression, and I checked the elco connected to its pin 8 (procedure as above), but without any succes. Removing this capacitor makes the hum much louder, so clearly it does something. I measured the DC current, because excessive current may overdemand the power supply, leading to hum. The current draw is 21mA from a 6V DC supply, and 53mA from the 9V supplied by the internal supply. I think this is rather high, but the schema does not give a correct value for the current. Excessive current can be caused by the AF amplifier, but I checked voltages on all pins against the schema and everything was OK, so probably excessive current is not the cause of the hum. It was suggested that perhaps thirty years ago, the speaker conus was more stiff, leading to reduced reproduction of basses so the hum was inaudible then. Speaking against this theory is that Doctsf also reports that hum suppression of this model is not sufficient.

Taking a look at the power supply, we see that there is no active stabilisation (the D2010 does have a stabilisation transistor in the PSU). This supports the theory that, for reasons unknown, Philips thought hum suppression in the D2243/D2214 less important than in the D2010, and so the weak hum we observed may be normal for this model. The first capacitor is connected directly to the (low impedance) power transformer and, when the radio is switched on, the second capacitor is placed directly parallel to the first. So, the audio amp is fed from a capacitor (of 940uF capacity!) connected directly to the transformer and rectifier. A better ripple suppression is given with the same capacity when there is some resistance between the two. I tested this with a 20 Ohm resistance placed in series with the power switch. And this was fully succesful, as the hum disappeared completely!

The resistor in series with the power switch means that it is also effective when using the radio on batteries. So, if you ever want to use this radio on batteries for some time, consider moving the resistor to the right in the diagram, so that it is only effective during mains operation. Why didn't Philips include one extra resistor during the design in 1982? I don't know. Possibly, this low level of hum was considered acceptable. Possibly, the speaker characteristics caused the hum to be inaudible in the first place.


Part of Gerard's Radio Corner.
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