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Thread: MF P140

  1. #1
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    Default MF P140

    Fired it up this morning using a homemade passive pre, sounds sweet but with plenty of grunt .Will strip it down this afternoon as I can now get close to the bench . What is the purpose of the switch at the back? input attenuation ?, all probably become clear on strip down .thanks again Si
    ray
    many a good tune

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    Had a quick look in Google Images - neat. It has side vents and is quite slim so good for stacking and bi-amping? Can it be used as a mono power amp?

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    Unfortunately the top is one big heatsink so stacking is a problem but certainly tidy looking, this one has no side vents (not for long) . As for using as a monoblock I cant see any reason why not .Struggling for any proper info on this amp at the moment so I am running on inspired guesswork .Fortunately I have all the bits I need and by this evening it should be back up and running (with a bit of luck)
    Last edited by rhmbus; 7th June 2015 at 16:08.
    many a good tune

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    Ray, I was going to do a P140 thread but I might as well just stick it here instead.

    The amp I gave you is a very early version and there were a few changes to later ones. There isn't a lot of info around but I do know someone who worked on these so I'm hoping he may be able to help. The switch at the back is input attenuation though I never understood the reason for it and it's not used on later amps. The switch is deleted on later models. There are also a few component changes on later models and a couple of resistors are deleted. I'll put some pics up later so you can see the changes to the circuit board.
    Si.

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    re capped ,mains tranny sorted ., fitted a set of proper binding posts and mains lead replaced all back together . will have a listen after GP ,feel nackered after 4 hours at bench so I can only imagine how you are feeling .what do you think of this for remedial work
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    many a good tune

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    Jeez, I've not had my dinner yet, good job.

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    Bloody hell Ray that looks awesome mate! Why have you not got a dressing on it?
    Si.

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    out of all the things in the world to be allergic to I cop for hard work and plasters
    many a good tune

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    My mother-in-law had staples across her neck after a thyroid operation. I called her bride of frankenstein and got another slap (she's always slapping me lol).

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    got that many of them (50) that if I move around I effect the magnetic pole .
    many a good tune

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    Keep out of the kitchen!

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    Quote Originally Posted by rhmbus View Post
    out of all the things in the world to be allergic to I cop for hard work and plasters
    I love hard work Ray. Didn't realise how much I missed it. The last week has really taken my mind off all this hifi bollox
    Si.

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    sounds nice , in fact listening to the Nice .New caps seem to be settling ok ,have been running with a passive pre amp that I toshed together to use with the Christmas system .BUT I have an Armstrong 625 I bought for bits with its amplifier stage toasted ,the pre amp and fm boards look ok so I intend to use it with the p140(god I must be boored but its better than going shopping)
    ray
    many a good tune

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    Ray, I'm having issues uploading pics again tonight. I must get my mac mini sorted and then I can use a decent picture hosting site. Anyway I've been messing with one of my son's P140s today and I replaced the1uf input caps with some nice Wimas which has resulted in a very clean sound. I'd already replaced all the electrolytics as a matter of course but left the film caps until replacing the inputs today. I'll think I'll replace the feedback caps and leave it at that. The feedback cap is critical and needs to be a good 'un. Did you uprate the smoothing caps Ray? The rail voltages are well above the voltage rating of the original smoothing caps so I upped those in my son's amps to 100 volt working. Some slight alterations are needed to get the bigger caps in but it's worth the effort. I uprated the skinny cables from the pcb to the binding post too. I'll try and get some pics up in the morning so you can see the difference in the boards. The later board doesn't show any signs of scorching the pcb like the early ones do.
    How did you get on with the transformer Ray? I know it worked ok but the insulation was in a bit of a state. I've ended up sending a pair to Terry at Canterbury Windings to get sorted out.
    Si.

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    Si ,uprated the smoothing caps to 100 volt 105c to be on the safe side (and I already had them) as you say a tight fit . Upgraded the wiring to the binding posts as you did and replaced mains lead with 3 core/added earth .Shelved the idea of using the Armstrong as a preamp as I have a buyer but ordered a Velleman kit for about 15 and it looks a decent basic volume tone control cct. Had a look at the transformer don't seem to bad so I will wait till another one comes along . Listening to the amp at the moment, invested a fiver on a triple cd collection from Sainsburys called Magic Bus, a reasonable investment and a fathers day treat to myself and it sounds lovely , I have always liked the way Michaelson voice his amps even if they look like a cross between a boot scraper and a waffle iron will get some photo`s together and we can compare notes
    cheers again Ray
    many a good tune

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    Haha, I actually like the casework on this early stuff. I think it's better than the thin pressed steel of the later offerings like the E series and I like the unique shape. I also happen to like the voicing of these amps. It's a shame that the build quality was not always as good as it should have been. I must admit I've always liked MF kit ever since I bought my first MF amp and I'm pretty sure that's the one you have now I don't remember having another one with the gain switch and I think it must be a very early amp. A piece of MF history maybe.

    Glad you fitted bigger caps, they do need it imo.

    The matching 3A preamp has passive outputs as well as outputs with gain and I always thought that the passive output was a better match sensitivity wise but lacked the balls of the other output. The B4 unity gain preamp I've been using addresses those issues. I also have some Avondale low gain boards which I might try.
    Si.

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