Philips 521 Lamps (22RH521)
 

I acquired one of these good looking Philips amplifiers and after a switch clean it was all up and running with one problem, the stereo light didn't illuminate.

well the lampholder had a zener between it and the power light.....strange so I got the schematic and typical Philips complex circuits the lamps were fed off the 45 volt supply via a 560 ohm resistor then 3 lamps, 2 meters and the power light, in series then a 5v6 zener to ground with the stereo light wired across it and a switch to bring it in circuit !!

Well the present lamps only glowed as they had been replaced with .1 Amp instead of 50 mA ones so I thoght this is not going to a reliable circuit and if one lamp goes they all fail like christmas tree lights.

Well a little while ago I bought 100 white 1 watt domed leds so I pressed these into service first filling the old bulb holder with gluegun and sticking the led on the end then had wired the led to the original connections, I found 27K in series with the 2 meter led's gave a nice light and the power and stereo lights had 10K each in series as they looked better a little brighter, I used the old switching wires to turn the stereo led on and off.

The result, everlasting lights that look original, the only modification I would do is wire the leds down the inside of the old bulb holders as the contacts stick out a little and could short if space is limited, there was plenty of space in this case.
Hope this is useful to someone with the same sort of problems, I have used these led's several times now for dial lights as when under run the look good and the domed top means they don't produce and intense spot light most led's

Re: Philips 521 Lamps (22RH521)
 

I have a similar design Philips 720 receiver/ amp. it works fine except that most of the dial lamps(there are many) have failed.looking at the circuit, there are 3 or 4 different types of lamp, different voltages etc.Your LED solution looks promising, I will investigate further, thank you.
Bill