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Quad 306 innards - and caps?

Discussion in 'classic' started by miktec, Aug 22, 2022.

  1. miktec

    miktec retired

    Finally got around to taking the lid off a 306 that I bought some months back - to be fair, it's in an awkward place and I am damned lazy ....

    Was pleasantly surprised - looks quite clean and nothing I saw made my hair stand on end:

    Quad 306 innards
    by mik tec, on Flickr

    Only slight concern was the vaguest of bulging on a couple of the big boys:

    Quad 306 bulge
    by mik tec, on Flickr

    Not too worried but thinking it might be a good pre-emptive move to replace them at some point soon.
    I have these in mind as drop in replacements , same specs and slightly smaller dimensions - so good to go:
    Nichicon 4700μF Electrolytic Capacitor 50V dc, Through Hole - LLS1H472MELB

    Obviously done the obligatory Google search and the resultant discussions on forums (including PFM) hovered between same value - or upping to 6800uf/63v, usually Kendeil.

    No problem either way, but what I couldn't find in any discussion was the reason for upping the value (apart from bigger is better, price and/or dimensions)

    Anyone venture a sound motive for upping before I bite the bullet and order?
    Last edited: Aug 23, 2022
  2. chartz

    chartz If it’s broke fix it!

    I upped mine to 6800 µF 63 V 105 degrees, simply because they fitted and that’s what I had. Go ahead.
    The bulge is just the plastic top I guess. Nothing to worry about then.
    The Spragues still measured fine by the way, so I kept them.
    miktec likes this.
  3. Barrymagrec

    Barrymagrec pfm Member

    If that really is bulging definitely replace them sooner rather than later, if they leak under the base it will make a nasty mess. Sometimes it is only the plastic which has warped and the cap has not bulged, easily checked by pushing down on the bulge.

    Personally I wouldn`t up the value,Quad had a fairly good idea of what value to use.
    miktec likes this.
  4. Zombie

    Zombie pfm Member

    There are some Mundorf boutique caps at hificollective if you want to up the game. Replace the other elcos while you're at it.
    miktec likes this.
  5. miktec

    miktec retired

    Thanks for the comments chaps ...
    Managed to get a better view of them this evening - the one on the left in the pic above has definitely got a right cob on.
    The bulges are also rock hard (no plastic flex) so the amp is on the bench for the foreseeable....

    Will order the Nichicons ... all the small caps look absolutely fine so they will stay put ;)
    Last edited: Aug 22, 2022
  6. chartz

    chartz If it’s broke fix it!

    They look fine, but they are past their prime. While you’re at it, replace them too, really.
  7. Barrymagrec

    Barrymagrec pfm Member

    G T Audio likes this.
  8. TheDecameron

    TheDecameron Unicorns fart glitter.

    What’s the issue with using higher capacity caps, is it something to do with in rush current?
  9. Barrymagrec

    Barrymagrec pfm Member

    Yes, it could be depending on the rectifiers. In theory the higher peak current will also cause greater transformer heating but In general it won`t cause a problem but equally probably won`t be an improvement.

    Different amplifiers will have differing characteristics and limitations to consider if you want to bump up the reservoir caps.

    Valve amplifiers using valve rectifiers are much more critical and very careful study of the valve ratings and transformer impedance should be carried out before deviating from the original specified caps.
    miktec and TheDecameron like this.
  10. miktec

    miktec retired

    Ah - go on then! ... you talked me into it.

    You guys will have me destitute at this rate :D
  11. Zombie

    Zombie pfm Member

    hificollective sell Nichicons btw, but I used Mundorf 125 C PSU caps for my 909.
  12. miktec

    miktec retired

    Thanks, had a look - but twice the price of RS for 4700uf (and too tall) .... so maybe not.

    Anyhoo - ordered already so just a case of waiting anxiously for the mailman.
    Last edited: Aug 24, 2022
  13. miktec

    miktec retired

    ... caps arrived last week but have had to wait in the wings a while:
    by mik tec, on Flickr

    until today when I had time and space to sort them - went quite easily really and initial test in garage confirmed all went well :)

    Quad 306 recapped
    by mik tec, on Flickr

    (BTW - the front plate isn't really bent - the phone camera is just a bit crap)
    Last edited: Aug 29, 2022
  14. chartz

    chartz If it’s broke fix it!

    Good. May we see the other side please?
  15. miktec

    miktec retired

    Would love to - but unfortunately the case is back on and its in the rack now ..

    Not much to see to be honest - lots of little blobs of solder :D
    Last edited: Aug 29, 2022
    booja30 and chartz like this.
  16. traf

    traf pfm Member

    That's the great thing about 306s - so long as you know which end of a soldering iron to hold, 6x caps + 15mins and you're good to go :)
    Gervais Cote, miktec and Fatmarley like this.
  17. chartz

    chartz If it’s broke fix it!

    The very definition of elegance.
    booja30, miktec, Barrymagrec and 2 others like this.
  18. Glenn2

    Glenn2 Member

    Sorry for reawakening this thread, I have in my possession a tired 306, still on its original capacitors. It sounds very nice at low volume anyway...

    Lots of info around on what people used for the main smoothers, not so much on C7, the 47uF/63V 'Marcon' part, or what its duty is.
    Mouser have all the Nichicon 'audio' caps, the KA is perhaps a contender being 105deg. 50V should be fine here I think.
    I wonder what Dada supply in their kits? The kits don't seem to be available, and really I want to restore it rather mod it anyway.

    For the big caps, I'm toying between these two:

    The Kemet ALC10A is the current incarnation of the BHC ALC10A that is currently fitted (albeit now 63V not 50V), and I like the idea of replacing like for like.
    The EPCOS are 5000hrs (vs 13000hrs for ALC10A) but that's rated at 105deg not 85deg. I think maybe these are the ones in the Dada kit. I saw a thread on here where somebody preferred the Dada-supplied EPCOS to the Kendeils. The 50V version is also 30mm diameter rather than 35mm which means they won't be squashed against the rectifiers like the original BHC ones are. They are lower ESR than the Kemets (33mOhms vs 91mOhms) but I don't know if that's good or bad in this application. The 91mOhms seems higher than any others that actually specify it.

    Any advice welcome, especially on the 47uF.
  19. Zombie

    Zombie pfm Member

    I used Mundorf elcos as the big reservoir caps in my 909. Very good. Replace all the other elcos, too, with good Nichicons or such.
  20. miktec

    miktec retired

    Main thing to watch out for is the height of the big caps ...the 306 is very shallow.
    Can't remember the limit at the 'mo (30mm from memory) but the Nichicons I got were spot on, a doddle to fit, and have performed brilliantly (25mm high)

    From memory, I think I went for Nichicon for the smaller values too (or possibly Panasonic looking at the photo)

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