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Late 80s 2 box Croft Mega Micro :)

Discussion in 'classic' started by Dowser, Sep 14, 2020.

  1. Dowser

    Dowser Learning to bodge again..

    For my sins, I have just bought one of the above. After running my modified Croft Micro II happily for 12-15 years, I just could not resist this rare item. It comes with problems;

    - one of the B+ transformers for line stage is open circuit so line stage is sharing one transformer
    - original ecc807 phono stage Valves have been swapped to JAN 5751 (ecc83) - Logic was that the ecc807 is too hard to find and expensive nowadays

    I need to decide what to do - I’m tempted to contact Glenn and ship it to him for service/repair - I could do it myself, but would rather have it sounding as Glenn intended to be honest, and I wouldn’t be able to ensure that.

    I’ve never seen one come up for sale before - does anyone have one, or heard one?

    thanks, Richard
     
    torstoi and Vinny like this.
  2. Vinny

    Vinny pfm Member

    Forgive pun, but that sounds, VERY interesting.
    Having moved from a micro with single ECC82 cathode follower to one with two 12BH7 push-pull output for a very nice improvement in sound, I can only imagine that, running correct, this will be rather special.

    I have browsed online many times and found various descriptions of Micro types/variants and the like, but, not so far as I recall, a two box one. What does the label reckon it is? A Mega Micro? Serial no.?

    I'd have a discussion with Glenn first, if it were me, see the lay of the land.

    i am now going to trawl the www to find what the hell a ECC807 is/was....
     
  3. Vinny

    Vinny pfm Member

  4. Vinny

    Vinny pfm Member

  5. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    I am pretty sure I have a pair of ECC807
     
    Dowser likes this.
  6. Dowser

    Dowser Learning to bodge again..

    and how much would sir like for them? :)
     
  7. Yank

    Yank Bulbous Also Tapered

    ECC807 amplification factor of 150!

    VTL used to make a phono+line preamp that used two ECC807s - one triode for each stage. Inverting feedback RIAA EQ wrapped around one stage. I don't imagine many were sold.
     
  8. Vinny

    Vinny pfm Member

    Gain of an 807 is less than an 83 and an 83 is around 3, if memory is correct. Entirely received wisdom, but in this sort of application, gain doesn't mean too much.

    Familiar with any Croft pre', Yank?
     
  9. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Eh? Gain of ECC83 = 100 ECC807 = 150
     
  10. Vinny

    Vinny pfm Member

    Agreed numbers wrong. But otherwise not according to the Valve Museum. At the least, an 807 is supposed to be lower than an 83. Check the link above.
     
  11. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    I'd probably sell them but I'll have to give it a think... It's not like I can just get some more and nothing else has MU of 150! I've thought before that they could be rather good in a phono stage but the fact that if one ever failed then it's game over for my one-off ECC807 phono stage has somewhat put me off... Would prob work reliably for many years of course!
    They are used genuine Brimar ones. I'll prob PM you later.
     
  12. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Nope it's 150. Google for a data sheet.
     
  13. Vinny

    Vinny pfm Member

  14. Dowser

    Dowser Learning to bodge again..

    Thanks all. Reality is Glenn also swapped to ECC83s in the phono stage, and my Micro II (also late 80s) uses them. But the Mega Micro was Glenn taking his design as far as he could. I’ll discuss With him best options I think.
     
  15. Dowser

    Dowser Learning to bodge again..

    Does anyone have a current email for Glenn - the old croftacoustics one is dead. Please PM me if you do, thanks.
     
  16. Dowser

    Dowser Learning to bodge again..

    Actually, that’s still his email on the website, I try calling tomorrow.
     
  17. Dowser

    Dowser Learning to bodge again..

    Woah, arrived today - Mega Micro serial #115, 230v. Same crappy colors as my Micro II, basic but still higher quality. Love it! Hopefully pictures at weekend.
     
    Vinny likes this.
  18. Dowser

    Dowser Learning to bodge again..

    Wow - covered in nicotine, inside and out - foam cleansed covers and front panels a little only so far, but it really needs a full strip down and deep clean - it's a real step back into the past, just how brown and sticky everything gets when you smoke somewhere inside disgusting! (and I'm a smoker) :)

    Just did quick check to make sure it was safe to switch on - no idea if original, but transformers all sitting on rubber strips, all going gooey and needs replacing. Phono valves not same brand, and as sold same single B+ transformer is powering both line stage valves (it's supposed to have one each).

    So, plugged in - how does it sound? Nice, detail information somehow much clearer than with my Micro II, background more silent somehow, but not what I considered a weakness of the Micro II. A bit harsh at first, but after an hour is really quite impressive (no idea when it was last used). Think I'm going to ask Glenn to check it over - I'd like to ensure the phono stage swap of valves was true to his design (but I have not tried phono stage yet - later this evening I guess).

    Anyhoo - photos (I'd be very interested in hearing from another owner - does this all look right?);

    Pre
    [​IMG]
    Phone stage on left, line on right
    [​IMG]
    [​IMG]

    PSU
    [​IMG]
    Transformer bottom right is new, replacing OC one for one channel of line stage - haven't fully traced wiring yet, no idea what it's doing, both line stage B+ are connected to other original transformer :)
    [​IMG]
    See original wires removed, also everything disconnected from blue smoothing cap on right
    [​IMG]

    It's competition, my original and mildly modified Micro II (had to pop it open as I loosened an RCA socket removing cables to fit the Mega Micro)
    [​IMG]
    Mustard output caps only electrical mod
    [​IMG]
    Hugely over-specced smoothing capacitance, plus a single Alps Blue
    [​IMG]

    Thanks, Richard
     
    torstoi likes this.

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