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Manticore Mantra repairs

Discussion in 'd.i.y.' started by cj66, Aug 18, 2022.

  1. cj66

    cj66 pfm Member

    Like a Dalek out of its exoskeleton.

    [​IMG]

    Had this lurking on the phone.
     
  2. suzywong

    suzywong Wot, no electrons?

    I met Doug once….in a hotel in Toulouse. Would have been about 15 years ago. Business trip for the satellite programme I was on. Sitting in the bar of the Mercure Hotel reading a hifi mag, and struck up conversation with the other Brit in the bar; turned out that not only did we work for the same company, we were also working on the same Satcom programme.

    Got through several beers and lots of hifi talk!
     
    Craig B likes this.
  3. Craig B

    Craig B Re:trophile

    Presumably yours is the version that requires the matching X-PSU.

    Here's one, same designation on the PCB, presumably came with a wall wart 12VAC adapter.

    [​IMG]

    Anyway, judging by the number of small transistors, the MC section is in the back half with MM up front. Can you read the values on those Styroflex caps that are located just below ICs 201 and 301?
     
    cj66 likes this.
  4. cj66

    cj66 pfm Member

    ^^^^^

    It has a DIY power supply, I depopulated the on board rectification, regulation and splitter/doubles.

    Those C207 & C307 are....

    [​IMG]

    Further to the front are C212 & C312

    [​IMG]
     
    Last edited: Aug 22, 2022
  5. cj66

    cj66 pfm Member

    An interesting development.
    The new 6.8k resistor arrived today so I removed the existing charred one. On measuring it I was surprised to see 14.9k ??? The damaged colour bands are obviously useless for cross checking, seems odd.
     
  6. Craig B

    Craig B Re:trophile

    Remember, Rega's earliest resistor was a 15k carbon type, had UK mains down to below 100V.

    Re: your X-LPS, I'd be wanting to change out those 220pF polystyrene for lower pF of the same voltage rating and type, myself. It would appear that less than 100pF are rather rare with these, though.

     
    Last edited: Aug 22, 2022
  7. davidsrsb

    davidsrsb pfm Member

    The photo looks like brown-black-orange, brown tolerance, which is 10k 1%. The black could easily have been green before cooking and the tolerance might well have started off red (2%) or gold (5%), so 15k is possible
     
  8. Craig B

    Craig B Re:trophile

    Keep in mind that the original Philips spec of 6.8k was to bring the mains down to 110V for general usage of these motors.

    Most turntable makers found that somewhat less voltage allowed for quieter running. That is, provided that the voltage feeds to each motor phase were well balanced (which they often weren't).

    Have a look at this vintage Planar 3 restoration by New Zealander, Owen Young (RIP). Through his own experiments, Owen came up with the exact same capacitor values* that Rega had found optimal for Planar 25.

    * 'values' as two caps were required to come up with the specific sum value (same as Rega did for P25, although Owen had not been aware of this prior).
     
    Last edited: Aug 22, 2022
  9. cj66

    cj66 pfm Member

    I'm pretty sure I have some 15k 3w resistors lurking in a parts box.
    I definitely have 68pf polystyrene caps but they'll be 630v almost for sure...

    Thanks for all the further comments.
     
  10. davidsrsb

    davidsrsb pfm Member

    Also remember Philips were designing for 220V nominal

    630V rating for the MM loading capacitors is fine, just a waste

    I don't like using a series dropper capacitor as it injects all the supply harmonics and noise into the motor. A resistor acts as a filter.
    If a series capacitor fails short, your expensive motor is toast. Resistors reliably fail open
     
    a.palfreyman likes this.
  11. cobbers

    cobbers pfm Member

    i've bought low value polystyrene through uk epay suppliers before now because of low prices inc post.
    68pf 63v 10 off for £4.49
     
  12. Craig B

    Craig B Re:trophile

    Linn (technically Ariston) may have been the first to do this with the pre-Valhalla network, both on the PCB and with the prior Molex terminal block.

    Here's the big Plessey on PCB...

    [​IMG]
     
    Last edited: Sep 4, 2022
  13. cj66

    cj66 pfm Member

    It turns out I have some 68pf 120v caps as well but no 15k 3w Rs.

    Those 220s are probably good news for the Elan on the deck now, that needs all the help it can get for HFs and is rated up to 400pf total so pretty close.
     
  14. Craig B

    Craig B Re:trophile

    With both Elan and Elektra (same 560mH generator) Goldring were pretty generous with a suggested capacitive loading range of 150 - 400pF.
     
    Last edited: Sep 9, 2022
  15. colasblue

    colasblue pfm Member

    That isn't a very big range actually, particularly if you factor in an unknown armlead capacitance which will vary with length.

    The actual values of cap you could buy are 100or less ,150, 220, 330, 470 so that's actually only three notches on the available range really.
     
  16. cobbers

    cobbers pfm Member

    Built in switchable caps into my DH-110 to give 5 options from 30 to 200pf + cables.
     
    Last edited: Sep 9, 2022
  17. Craig B

    Craig B Re:trophile

    I only mention the 150 - 400pF because I don't recall ever having noticed another MM cartridge having such a broad capacitive loading recommendation, at least not since Shure Bros. pioneered the trend of quoting such back with the introduction of V15 Type II in 1966. Prior to this, only recommend load impedance was listed, in Shure's case often with coil inductance and DC resistance quoted such that the committed enthusiast could do their own calculations.
     
  18. cj66

    cj66 pfm Member

    The thought did cross my mind to fit sockets in the cap positions to make swapping easier...
     
  19. cobbers

    cobbers pfm Member

    The Hafler has loading sockets on the inside of the input board but it's a pain to get to and small value caps invariably have very thin wires which aren't gripped by the sockets (bought 33/82/120/160pf which when added to the fundamental 30pf of the phono circuit gives 70 to 200pf - plus left a switchable open circuit position).
    The switch and wiring adds about 10pf on it's own.
     
  20. cj66

    cj66 pfm Member

    Next stage;

    The XLPS now has sockets where the MM loading caps were and 68pf installed.

    I also have one of @Mike P blue belts popped on.

    [​IMG]

    Motor readjusted after being fettled and all is running virtually silent. Speed is much improved over the old knackered belt.

    I haven't yet had time for a listen and final tweak before fitting my spanking new RigB AT-VM95ML, which is still waiting in its box.



    Postimage hosting observation;
    I see a few members are using this service but the post only contains thumb nail images and links. Even after following the link the image is still too small/low quality to view zoomed.
    My image above above seems fine. Are peeps linking incorrectly or is this deliberate?
     

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