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 Philips model 224
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 Return to top of page · Post #: 1 · Written at 8:41:32 PM on 6 October 2021.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1484

This radio had been in the garage to provide music on the odd occasion that I was using the workshop. Recently I noticed a marked drop in sensitivity, so today I decided to do something about it.

First thing, remove the 6 screws holding the cyan plastic case on and push it out of the way. The case can't be entirely removed because there's no cutout for the power plug to fit through.

Valve line-up is standard: 6AN7A, 6BH5, 6BD7, 6M5, 6V4. The radio has no paper capacitors.

Turn on, now can't hear 2UE at all now, but 2BL still audible at low volume. Since the power supply is the most vulnerable part of a radio, measured everything but it was ok. The filtered HT was spot on at 250 volts. Voltages around the output valve seemed ok too. Poking around further afield revealed the G2 on the 6BH5 at just 4 volts. This voltage is also used on the 6AN7A, so it was amazing that the radio could pick up anything at all. This voltage comes from a 82k resistor which turned out to be open circuit. I used a 68K 2watt as a replacement, I figured it was close enough.

Switching back on, and it roared into life. Another easy job.

While I had it open I cleaned the valves and polished up the 6BH5's silver-plated pins. I also cleaned out the dust, before finally refitting the case.

I also noticed that the radio has a ferrite rod antenna, which means the external antenna that I'd always used before (the garage roll-a-door) was no longer needed - the ferrite by itself now produces more than enough signal from Sydney stations.


 
 Return to top of page · Post #: 2 · Written at 9:47:14 PM on 6 October 2021.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

One of the things people fail to realise with a superhet is that if there is a way for signal to get into the AGC it will carry back to the 2nd detector and give a weak signal. It may just get a strong station, or it may tune stations as a TRF depending on the front end.


 
 Return to top of page · Post #: 3 · Written at 12:39:00 AM on 7 October 2021.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1484

The ABC stations were still appearing at the correct places on the dial while it was broken, so I suppose the oscillator was still doing its job. It has its own supply, not related to the broken resistor.

I need to point out that I'm about 100km from the Sydney commercial stations (the ABC is a bit closer), however I expect any valve radio of mine to be able to hear them all, day and night.


 
 Return to top of page · Post #: 4 · Written at 12:57:02 AM on 7 October 2021.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

I can usually get 2CH at night from here & some stations across the ditch.

6AN7 is a Triode Hexode, So the is triode is the separate exciter and 82K is the common screen resistor, that is bound to make two RF tubes very unhappy.


 
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