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Old Philips 520 Integrated amp - where should I start?

Discussion in 'classic' started by beammeup, Nov 12, 2017.

  1. beammeup

    beammeup pfm Member

    I've picked up one of these old 70's integrated and not even powered it on yet in case there is a staged approach I need to go through first - noteworthy is the old 2-pin UK plug which may mean it's not been switched on for 40 or so odd years!

  2. Snufkin

    Snufkin pfm Member

    That plug could be an older continental plug and I am sure I have seen similar in the Netherlands.
  3. beammeup

    beammeup pfm Member

    This is the rear of the Philips showing the voltage settings. Can I just wire up a UK plug, plug it in the mains, and all should be fine?

  4. Rug Doc

    Rug Doc pfm Member

    What else are you going to do? Use it for decoration??!!

    It should be fine. Both marking on the reverse are for 240v so it's deffo a UK model. You'll love the glow from the vu's!!
  5. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Ideally wind it up slowly on a variac but you should be ok just plugging it in.... It's apparently tropicalised so that should help with its longevity in many areas.
  6. beammeup

    beammeup pfm Member

    A UK model with a 2-pin plug? I didn't want to just plug it in without thought and the case becomes electrically live thus dangerous or something.

    Actually yes - I don't expect good sound quality from an old bit of tin like this - so I am going to use it for decoration with them there VU's being the showy decor bit :)

    So 'tropicalised' means it's built to be more hardy than most - didn't know that thanks.
  7. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    As it says it means built with the high temperatures, humidity and likely mould etc etc of "the tropics" in mind and to have some degree of extra protection from these.
  8. Bob McC

    Bob McC Living the life of Riley

    Surely old kit like that should have an earth wire.
  9. Robert

    Robert Tapehead

    Since you wont have a variac (most people don't :) ) you can use the dim bulb method if the unit hasn't been operated for over 40 years.
    Basically it's a 60w light bulb placed in series with the mains inlet. Any major faults within the amp (eg shorts) and bulb takes the current surge. it can also help form the electrolytic caps running it on the reduced voltage for a short while.
    If the bulb flashes bright for a few seconds and then dims to a dull glow, that's usually a good sign. if it stays glowing bright you have a serious fault.
  10. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    /\ Top tip! I have couple of old incandescent bulbs with flying leads soldered on for just this but it didn't occur to me to mention it....
  11. toprepairman

    toprepairman pfm Member

    The old light bulb trick is very good advice.
    As you have such low expectations as to its' performance then prepare to be amazed. It may only be a modest 8 or 9 watts into 8 ohms but otherwise will perform every bit as good as anything else.
  12. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    One slight caveat with the bulb method, and yes it's pretty pedantic as it happens rarely, is that a sort of relaxation oscillator can be formed by the non linear resistance of the bulb and the start up characteristics of a small number of amps/"things under test". I have seen this happen. Disco light and unhappy amp.
  13. narabdela

    narabdela who?

    Nope. All the kit I had in the 70s was two pin.
  14. beammeup

    beammeup pfm Member

    Only 8 or 9 watts per channel - where did you get that info from?

    That wouldn’t power a fleas moped !

    Good to know someone here thinks it might end up sounding good - perhaps when I find a pair of hypersensitive horns to hook them up to (if it powers up and works) I can find out.
  15. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Erm... yeah 8 or 9 watts per channel... into 8 Ohms. I can see no reason, having looked at the schematic, why they didn't make it more powerful.. other than to make way for a higher priced model of greater output..
  16. toprepairman

    toprepairman pfm Member

    "Only 8 or 9 watts per channel - where did you get that info from?"
    From the picture of the rear panel where it states 15W sine into 4 ohms.
  17. Craig B

    Craig B Re:trophile

    Just a couple of points with regard to steps that I've followed over the years of collecting vintage amplifiers and receivers.

    1) Get yourself a digital multimeter, if you don't already have one. You don't have to be an electronics expert to test for DC on the speaker outputs. Even testing/adjusting bias and DC offset is pretty straight forward with a copy of the service manual to hand.

    2) Deoxit is your friend; those less often used tone and balance sliders in particular can get very noisy/intermittent with age/wear, none use, and environmental pollutants. The volume pot and bias/offset pots will likely need cleaning as well. I always try to 'exercise' away the contact resistance first before resorting to the spray. Should contact cleaner spray prove necessary, then follow up with a good full range end stop to end stop workout of pots and sliders will often have them working like new; if not then replace parts as necessary, assuming availability (many slide controls are unobtanium these days, bar having a parts doner amp available).

    BTW, low power or no, many of these lower negative feedback earlier '70s models (I.e. ~0.1% THD) can and do sound lovely.
    Robert likes this.
  18. beammeup

    beammeup pfm Member

    Still haven't powered it on. Lots of good advice. I will probably blow out the dust (if any) from the inside, and work the sliders back and forth many times before I switch it on. Any particular reason why Dexoit - what about switch cleaner or WD40 instead?

    Craig, do you gently acquaint your old bit of kit with the mains by powering it up with a similar 'load' in series with it either via a variac or by way of the low power incandescent bulb trick?

    I've found this YouTube video about testing thanks:
  19. idem

    idem pfm Member

    Switch cleaner - yes, WD40 - no, no, NO!
  20. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Wd40 can be used if you have no switch cleaner but the issue is it can get rather gummy after a while so it's best to use proper switch cleaner. Tektronix at one time recommanded the use of IPA and WD40 for switches in their oscilloscopes. Caig Deoxit is very good but it's a hell of a price compared to "normal" switch cleaner.. like £20 ish a tin IIRC compared to £2.50 ish...

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