Philips N3W24T car radio

[Tim]

Thisone was actually done last summer but I have only just got round to posting it. I wish it had looked as good as the finished car.

Still, the owner was pleased.

PHILIPS N3W24T

Transistorised car radio covering MW and LW bands.

C 1963. 6 or 12 volts DC, + or - chassis

This one was a “remote” repair, being collected from the owners doorstep when I happened to be working in the area. He had also thoughtfully included a copy of the Philips service information(but there is also a limited amount in the 1963 volume of the Radio and Television servicing series of books).

With six volts(negative earth) courtesy of my bench power supply, the fault report of “hiss but no stations” was verified. So a cup of coffee and mull over the service data lead me to suspect one or more of the AF117 transistors used in the RF stages of this receiver.
A quick look inside though told me this wouldn’t be as straightforward as it sounds. The board containing the suspect transistors could be removed of course, but in this case would have been extremely time consuming and fiddly.
I considered it wise to check though, before delving in, so I applied a signal to the wiper of the volume control which was clearly(and loudly) repeated in the test loudspeaker. As the fault was definitely on the RF side I took some voltage measurements with the radio running from the bench power supply. Voltages didn’t really tally on any of the AF117 transistors, although readings were about right in the audio stage.
I decided it would be prudent to change the transistors anyway, given their reputation. Another case of “change on sight”.
The troublesome transistors leads were snipped off as close to the body as possible (leaving the maximum protruding from the board) and tested. They all proved faulty, so AF125/CV1089 replacements were soldered to the remainder of the leads protruding from the printed board for previously described print side access reasons.
Upon the next test a faint signal was heard and the radio could be tuned across the band, but volume remained at the same low level irrespective of the volume control setting.
Oh great!! Out with the scope!
There seemed to be plenty of signal at the “top” of the volume control track, but it wasn’t getting through to the wiper.
The control was removed and proved to be faulty. As the shaft was non standard a repair was attempted but was un-successful. Fortunately a standard switched pot would JUST fit once the switch contacts were bent!!, (fortunately the other set of contacts could be used. We only required single pole switching) and the plastic shaft was modified to fit.
This meant cutting the shaft about 0.25 inches from the end of the threaded mounting, filing the end square and cutting a slot to accept the volume knob shaft. To ensure a perfect fit, the key at the end of the metal knob shaft was heated with a hot air gun and the plastic potentiometer shaft offered up, melting the two together in a snug fit, and the joint covered with a rubber sleeve.
The radio worked pretty well now, for about 10 seconds before a loud crackling appeared, every time it was switched on.
A signal applied to the base of the output stage transistors in turn proved the fault to the OC71. Although the suspect device tested fine with a multimeter, replacement cured the crackling.
Alignment made no appreciable difference.

OTHER STUFF

The owner had asked me to sort out an external input, for an external audio source such as an MP3 player. This was connected across the volume control with a 10 k resistor in series with the signal lead and a 0.47 microfarad capacitor in series with the screen to avoid problems if the MP3 plug touches the car chassis etc. Happily if one “fiddles” the waveband switch,(normally selected by pulling/pushing the tuning knob) by just pulling it out halfway so neither waveband is selected then the RF hiss disappears. Although the Germanium output stage is extremely quiet the audio quality wasn’t fabulous, but no worse than the radio on normal operation and certainly loud enough to be heard over the roar of the 1963 Beetle it was going to be installed in.

The photos show the set in mid repair/testing and finally installed in it's new home! (plus a gratuitous classic car pic).

[chipp1968]

Nice . where is the speaker on the car ? looks like right of stearing wheel .

['LIVEWIRE?']

I don't, of course, know about this particular car, but, AFAIK, the speaker in VW Beetles fits above the radio, the sound emanating from a grille in the top surface of the dashboard.
Correct me, if I'm wrong!

[GJR 11L]

Speaker is in the vertical surface of the dash, as Chipp1968 suggests.
There's no space at the top for a speaker as the screen is flat.

Nice job there, good to see a radio fitted that is of the correct period for the vehicle.

[Tim]

Nice job there, good to see a radio fitted that is of the correct period for the vehicle

Hi John

The radio was with the car when the owner obtained it. He was having the car restored and decided to have the radio done too!

Although it can't be seen in the Photos I uploaded, the others I have show the VW bears an "A" suffix )-Jan1st -DEC 31st 1963)so the radio may well have been fitted from new. The trim seems to match the dash very well!