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Thread: Critique of Croft 5C power amplifier, with a safety alert.

  1. #1
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 4,572
    I'm Alan.

    Default Critique of Croft 5C power amplifier, with a safety alert.

    EL84 power valves, who doesn't love them? With a good implementation they can be stunning, as is the case with the Croft 5C.

    It's a bit of a brute of an amplifier, very minimalist looks but a very solid case.




    It employs 8 EL84's in parallel push pull, rated very conservatively at 30W per channel but capable of 45W.

    The one small fly in the ointment was the discovery that the case wasn't connected to the earth terminal of the IEC input, hence why the safety alert. This is a must with this type of equipment, so any owner please check this or have it checked.
    Here is the correct connection to a dedicated screw/tag on the chassis, with the paint removed and serrated washers to ensure good contact.





    Another small problem occurred at switch on, I must have just caught the max swing on the mains. The mains transformer is a toroidal type and as many of you will know they can have very large switch on surges, particularly if no surge suppression is present, as in this case.
    The subsequent arc within the on/off switch was large enough to flash over to the other pole of the switch and blow the mains fuse and trip the RCB in the consumer unit.
    I think this was an unluckily timed occurrence but I have also changed the switch for a better rated one.





    Now everything is up and running listening can commence. As with any traditional valve amplifier the biggest arbiter of ultimate quality is the output transformer, with the 5C this hasn't been skimped on with some large quality units fitted.




    The circuit appears to be 'ultra linear' with tappings for the grid 2 connections on the output valves. As stated with the full complement of valves the output power is commendable but with a large heat output, so the case gets very warm with extended use.




    How does it sound you ask? Sublime.
    There is a real 'valve' organic texture to the presentation, a superb open fluidity to the music. I know the frequency response is very wide, due in large part to the quality transformers, so you are presented with a very full sound with nothing missing.


    A possible side benefit of using parallel output valves is that half of them can be removed and the amplifier still functions, of course with a reduced output power. Due to the different loading now presented to only one pair of output valves some crossover distortion is seen at high output, but an output of 18W is still achieved before this occurs.
    This arrangement could be of benefit if the full complement heat output was excessive for the particular installation arrangements.
    Half complement of output valves:




    Delving a little deeper into the specific design revealed a fixed bias applied to all output valves, namely -12V. Now whilst excellent operation is to be had with new or good condition valves fitted, it can be a problem when the valves become tired or near their end of useful life.
    I have known this arrangement to blow the HT fuse after a period of operation when the current flow through the tired valve(s) continues to increase with no limiting due to the fixed bias.
    For this reason I have converted this 5C to auto bias on all output valves, which will ensure a long trouble free use.




    A really stunning sounding power amp from 2003 I believe.
    Firebottle - for the no bottleneck approach.

    I love Hendrix for so many reasons. He was so much more than just a blues guitarist - he played damn well any kind of guitar he wanted. In fact I'm not sure if he even played the guitar - he played music. - Stevie Ray Vaughan

  2. #2
    Join Date: Jan 2013

    Location: Birmingham

    Posts: 4,216
    I'm James.

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    The Croft 5 power amps were some of his best sounding power amps and highly sought after.

    Let me know if you want to sell it.
    VPI Scout 1.1 - Ortofon 2M Black - Croft 25R+ - Croft Series 7 - Spendor SP2

  3. #3
    Join Date: Apr 2009

    Location: Near Saffron Walden, Essex

    Posts: 6,212
    I'm Dave.

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    That was from a time when Glenn had little input on the products produced by his 'distributor'.

    The original Series 5 was a different animal. That was good.

  4. #4
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 4,572
    I'm Alan.

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    I did wonder if that may have been the case Dave.

    The 5C is a very good sounding amp, I have checked over and heard an original 5 as well

  5. #5
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 7,422
    I'm Oliver.

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    Nice writeup Al, looking forward to giving this a listen. Maybe a mini bakeoff with the Krell is in order.
    Analogue: Technics SP10 MK2 > Phonomac AT-1010 MK6 tonearm > Ortofon Kontrapunkt b > Bigbottle Jfet MC Valve Phonostage (Telefunken Valves)
    Digital: Raspberry Pi 3+ With Allo Boss.
    Amplification: Nelson Pass DCB1 with Khozmo 48 Step Series Attenuator & Krell KSA100 MK2 Amplifier
    Cables: Bigbottle Speaker Cable & SPOTFIRE IC Cables & NEW SPOTFIRE Tonearm cable
    Speakers: Pioneer CS-77A

  6. #6
    Join Date: May 2008

    Location: A Strangely Isolated Place in Suffolk with far away trains passing by...

    Posts: 14,522
    I'm David.

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    I echo HiFi Dave's post above, as I saw and played extensively with the previous older fashioned looking Series 5 that used frame transformers throughout as I remember, sounded absolutely bloody marvellous and didn't look anything like as 'nice' as the one you've pictured. Before altering the basic design though, Glenn's no ignorant numpty and it would have been interesting to know why he did the biasing the particular way he did. He is an open kind of chap though as I remember, so maybe he'd approve of a third party altering it subtly in this way. i only say this because of well meaning Quad 303 fettlers who alter the supply board, not realising at all that the strange? design that was used, was used for very good reason and a more conventional way of doing it isn't ultimately as good I gather.

    I've owned a few older 'proper Glenn' Croft products and remember he took huge care to earth cases and stuff on my pre and amp samples - and still does now he's his own man! He can always service his and similar valve stuff and that also includes updates on old preamps and so on...
    Tear down these walls; Cut the ties that held me
    Crying out at the top of my voice; Tell me now if you can hear me

  7. #7
    Join Date: Sep 2016

    Location: Warwickshire

    Posts: 58
    I'm Spencer.

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    I bought my SH Spendor S8e last year based upon hearing them with a Croft 4SA. Lovely full bodied sound, just what I was looking for. Results with my Job 225 are not quite the same, so I’ve been on the look out for a 4SA lately.
    All I know is that the 4SA was the top offering from Croft at the time. Wondering how a 7r would compare, as they seem more readily available? Or are there other models that you knowledgeable chaps would advise me giving a try?
    The 5 looks great by the way.

  8. #8
    Join Date: Apr 2009

    Location: Near Saffron Walden, Essex

    Posts: 6,212
    I'm Dave.

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    Last year, I sold a pair of 7R monoblocks to a chap who had a pair of Series 4SA (mono'd) from new. He had some problems with the 4SA, which Glenn couldn't source the components for and was looking for a replacement amp. After a lot of listening to numerous amps, he settled on the 7R mono's.

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