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A vintage Quad thread.

Discussion in 'classic' started by Tony L, Dec 7, 2012.

  1. Radfordman

    Radfordman pfm Member

    Differences that I have noticed, and there are probably more;

    1/ The front panel, no Wattage input stated.

    2/ Main heatsink fins much thinner than later models.

    3/ Discrete rectifiers instead of the block AEI type bridge.


    4/ The big power supply and speaker coupling capacitors seem to last and last, not like the blue coloured ones.

    5/ Slightly different paint shades, but then Quad paint was a bit variable.

    (lower left is the early 303)


    6/ The output transistors are marked RCA 2N3055, later models are marked RCA 38494

    I'm not taking the 303 apart today to check the mark 1 boards. Had enough of that. I'm enjoying listening to the 303 instead!
  2. Tony L

    Tony L Administrator

    I'll have to check the 8xxx one for the wattage thing. Both mine have the thin heatsinks and I'm pretty sure the same rectifiers as yours (they look the same to my eye):


    Mine have both been fully rebuilt, the later one (above) with Dada boards, the earlier one is stock but new caps, trimmers and a couple of off-spec resistors changed (it is John's old and lovingly restored one I think mentioned upthread somewhere). I have a feeling 8xxx has the earlier transistors, 9693 certainly has 38494s as I had to source a couple as one side had been replaced with a later Motorola equivalent. The reason I suspect the earlier one has has different ones is John sent me a photo with the heatsink cover off and the RCA logo was very different (earlier design). I didn't think to check the transistor numbers.
  3. Radfordman

    Radfordman pfm Member

    Looks nice, your rebuilt one. I should really do some new boards, fibreglass with new components.

    Here is the duff original output transistor removed from my amp today:

  4. Tony L

    Tony L Administrator

    That's the RCA logo that's in 8xxx for sure.

    PS It's 8359, I've just checked. I'll be using it to drive my new Decca DK30 tweeters soon.
  5. Radfordman

    Radfordman pfm Member

    I presume that there will be a passive crossover used, connecting a 303 to the ribbon tweeters might be a bit risky? My friend recently bought some Mordaunt Short MS700's, he liked the treble, but the mid from the KEF B110 was not that good. He replaced the B110's with the Dalesford bextrene coned unit that is similar, and got a good improvement.
  6. Radfordman

    Radfordman pfm Member

    These are the transistors that I bought a while ago as replacements for the old RCA 2N3055 / RCA38494.


    I understand that the modern 2N3055 are not really suitable as the frequency response goes too high due to the smaller internal capacitance of the junctions, this can result in oscillation.

    The original RCA 2N3055 / 38894 have higher capacitance of the junctions, limiting the frequency response, and hence no problem with oscillation.

    From what I have seen the Motorola 2N3055H has this higher capacitance due to larger junction size, just like the original RCA devices.

    I have checked my repaired amp with a scope and see no evidence of oscillation.

    Has anyone tried 2N3055 and got oscillation?
  7. neilmack

    neilmack pfm Member

    Apologies if this question has been asked a thousand times before, but where can I get a pair of BULGIN connectors - I think the code is SA1862 - which plug into the back of my original model Quad Electrostatics? I have looked through the catalogues of the usual suspects - Farnells, CPC, etc without success. I'm assuming they are long obsolete. Anyone any ideas?
  8. Radfordman

    Radfordman pfm Member

    These are quite rare now, and usually expensive if you can get them. I have four! but they are required for my four 57's.

    Correction, I have five of these connectors, I was forgetting the one for my Williamson amplifier.

    An alternative is to replace with an IEC socket (really plug). I think this is quite common practice, but I have not done this.
  9. Radfordman

    Radfordman pfm Member

  10. Radfordman

    Radfordman pfm Member

  11. hifienthusiast

    hifienthusiast Vintage by heart

    These Bulgin connectors have become obsolete over ten years ago. I used to buy them from RS or Farnell. The places you can find them are eBay, Nick from the Emporium vintage hi fi shop or audio jumbles if you are lucky.
  12. Barrymagrec

    Barrymagrec pfm Member

  13. soverton

    soverton pfm Member

  14. Barrymagrec

    Barrymagrec pfm Member

    Yes, and with the pins forming an equilateral triangle, not flattened off to the top.
  15. jimpey

    jimpey pfm Member

    I have a pair doing nothing.

    Happy to send them to you if you haven't already bought a pair..

    They became redundant when OTA replaced the fittings with IECs during service.

    PM me your address (be Tuesday before I can post)

  16. chartz

    chartz Member

    Just happy to have given this somewhat dormant thread a new life!
    Still waiting for my OTA ESL 57s. They do fit IEC sockets in replacement of the old brittle Bulgin ones.
  17. neilmack

    neilmack pfm Member

    Jim, that's extremely generous of you.
    I shall send you a p.m.
    many thanks!
  18. chartz

    chartz Member

    Hi everyone!

    My OTA ESLs have been with me for a few days.
    I am having a hard time positioning them in my largish dedicated listening room.
    I do have the sweet spot but there is not much width or depth : the sound clearly comes from the speakers, even though voices coming from the centre are really jumping out to me just in front of them.
    I have some work to do, in other words !

  19. ghostbusters

    ghostbusters pfm Member

    Hello all, I would wleocme some guidance as to if I have made a big booboo.
    I decided to spray the switches on my Quad 22 after getting it out of storage after 4 years with some contact cleaner as I was getting some static . I guess I got some on the buttons as well.. I am not what happened next but all the selector buttons literally split apart(cracked) and fell off when I started pressing them to work the switches. Would contact cleaner cause such as issue or have they just disintegrated with old age? Many thanks in advance.
  20. Tony L

    Tony L Administrator

    Chartz, I suspect you are too far from the 57s for convincing imaging, I’d move the chair forward and toe them in accordingly. In many ways it is best to think of Quads as big headphones and sit fairly close in an equilateral triangle. That is where the magic happens IME.

    ghostbusters, not something I’ve ever heard of, but I’ve never had a Quad tube rig. I’ve certainly had no problem using Deoxit on a Quad 33. I wonder if the post to which the button clips is slightly porous and swelled up slightly with moisture? A real pain anyway, I guess you now need to source a basket-case donor unit with good buttons.

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