No ..., i can asure you, in reality there is an more than just noticeble difference of performance for P170/P270/A370, when equiped with 2SJ162/2SK1058 ..., the specsheets are rubbish and just pure "cut and paste" ...The specsheet does not tell the true matter, total THD/IMD is much worse in total value and more servere the raise of the curve starts in the midrange.
The true matter is that some years ago, i did perform a lot of testing among others of the entire MF range using an Audioprecision, in these circumstaces i will mention: B200/P140/P170/P270/A370 & P270-2 ..... the last one made our firm believe somthing was utterly wrong at the first audition of it ..., we then inspected the P270-" and did not locate any viseble failure, next i made b2b test of P270 vs. P270-2 .., audible and messureble two very different amps, dispite when looked at for instance the Hitachi speecsheets "tiny" psysical difference
Ps. B200/P140 has one pair 2SJ50/2SK135 each ch.
The true matter is that some years ago, i did perform a lot of testing among others of the entire MF range using an Audioprecision, in these circumstaces i will mention: B200/P140/P170/P270/A370 & P270-2 ..... the last one made our firm believe somthing was utterly wrong at the first audition of it ..., we then inspected the P270-" and did not locate any viseble failure, next i made b2b test of P270 vs. P270-2 .., audible and messureble two very different amps, dispite when looked at for instance the Hitachi speecsheets "tiny" psysical difference
Ps. B200/P140 has one pair 2SJ50/2SK135 each ch.
Those are probably the date codes not the type number
Originals are actually 2N3055 and MJ2955 marked as A1N and A1p
MJ15003 and MJ15004 can be used as an improvement.
hi,
can anyone help me out with my MF P140. Im getting a very hot resistor,so hot it glows red. its rated 220hm probs 5watts. i'm not sure of the cause. I swapped the transistors over with the other channel but i get that same resistor getting hot,so i know that's not the cause. i will try to upload a pic. anyone else had hot resistor issues? what could be the cause? i would love a shematic or service manual if anyone has a copy.
thanks.
can anyone help me out with my MF P140. Im getting a very hot resistor,so hot it glows red. its rated 220hm probs 5watts. i'm not sure of the cause. I swapped the transistors over with the other channel but i get that same resistor getting hot,so i know that's not the cause. i will try to upload a pic. anyone else had hot resistor issues? what could be the cause? i would love a shematic or service manual if anyone has a copy.
thanks.
There aren't any neat, service manual schematics available for early MF products. All we have is hand drawn versions that have to be guesstimated across several models such as the P series amplifiers. They do seem to be similar apart from rail voltages and number of output Mosfets. See earlier posts in this thread and you will get the idea. There are a few about like one for the A370 but they can only be indicative, as the posts in threads advise
Here is a discussion of the problems involved with many early MF Mosfet models. It is not pretty. http://www.diyaudio.com/forums/solid-state/166250-musical-fidelity-p150-owners-take-note.html
MF typically used power resistors in series with the load and I'm guessing this is what is hot, indicating a blown or shorted output stage, caps etc. When you locate the likely problem, the T03 Mosfets can be substituted with Profusion Exicon parts or Magnatec Alfet parts if needed. Expect to have to do a lot of replacements in there including the main electrolytics and the reassembly of the case is not simple - the cover is part of the heatsink.
This is not a simple model for repairs.
Here is a discussion of the problems involved with many early MF Mosfet models. It is not pretty. http://www.diyaudio.com/forums/solid-state/166250-musical-fidelity-p150-owners-take-note.html
MF typically used power resistors in series with the load and I'm guessing this is what is hot, indicating a blown or shorted output stage, caps etc. When you locate the likely problem, the T03 Mosfets can be substituted with Profusion Exicon parts or Magnatec Alfet parts if needed. Expect to have to do a lot of replacements in there including the main electrolytics and the reassembly of the case is not simple - the cover is part of the heatsink.
This is not a simple model for repairs.
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ok thanks ian. The more i read about MF the more it starts to make sense. There's deffo DC at the speaker outputs as i used a tester speaker and the coil burned out. I did find those exicons on the bay, so would you recommend replacing the transistors anyway? Maybe that would stop the resistor burning out as it is linked directly of the casing of the K135. i noticed that the transformer is getting hot aswell, is this typical of MF early amps?
thanks.
thanks.
In your previous post, you concluded that the MOSFETS were OK because you swapped them and the resistor still became hot. Was that because the other channel from which you took the parts was originally working or were both channels dead?
Pressing on...
The threads here give a pretty unequivocal view on MF engineering and describe the high case temperatures well enough but that direct soldered resistor connection should not be repeated. Fit a small, 3-4 mm hole diameter eye terminal to the resistor lead and bolt this with the most suitable MOSFET mounting bolt to its case that way. Ensure that new mounting bushes (which you should also consider along with mica washers and correct grease) don't prevent reliable contact with the MOSFET case. The transformer does run hot on these - it is undersized but will heat even more due to the power burning up in the shorting resistor. It goes without saying that you don't place these amps in tight places or position anything near or on top of them. In this country, it took little time for failures of those P & B series amps to appear - few survive apart from those coming from deceased estates, with little use.
Failed MOSFETs are likely not the only casualties. You should check all resistors when the semis are removed and measurements should be less confused. Check supply voltages to the IC and its output which should be close to 0. Replace all heat damaged parts and, like the earlier posts urge, uprate the main electrolytic voltage rating to exceed the rail voltage by at least 10% - if required. However, don't waste money on boutique parts - MF certainly didn't! The MPSA93/43 (or similar) driver transistors are also doubtful after many years of stress.
Don't buy Exicons or any semiconductors on Ebay, particularly from HK traders. If there are difficulties buying EXICON brand direct from Profusion on the net, go to Magnatec and get the same parts branded ALFET. The prices are better when buying from the distributor this way, at least.
Farnell/Newark/Element14/CPC also market ALFET but the premium price they ask in my area makes them unviable. YMMV
Counterfeit Transistors
Suitable Magnatec part numbers are ALF08N16K and ALF08P16K.
Profusion EXICON TO3 parts are ECF10N16 and ECF10P16 . There are higher voltage options that could be used if availability is a problem. Don't be fooled by the apparent discrepancy in brand part numbers. One is derived from the peak maximum current rating and the other is continuous maximum current but they are actually the same chip, if you read the data sheets.
Pressing on...
The threads here give a pretty unequivocal view on MF engineering and describe the high case temperatures well enough but that direct soldered resistor connection should not be repeated. Fit a small, 3-4 mm hole diameter eye terminal to the resistor lead and bolt this with the most suitable MOSFET mounting bolt to its case that way. Ensure that new mounting bushes (which you should also consider along with mica washers and correct grease) don't prevent reliable contact with the MOSFET case. The transformer does run hot on these - it is undersized but will heat even more due to the power burning up in the shorting resistor. It goes without saying that you don't place these amps in tight places or position anything near or on top of them. In this country, it took little time for failures of those P & B series amps to appear - few survive apart from those coming from deceased estates, with little use.
Failed MOSFETs are likely not the only casualties. You should check all resistors when the semis are removed and measurements should be less confused. Check supply voltages to the IC and its output which should be close to 0. Replace all heat damaged parts and, like the earlier posts urge, uprate the main electrolytic voltage rating to exceed the rail voltage by at least 10% - if required. However, don't waste money on boutique parts - MF certainly didn't! The MPSA93/43 (or similar) driver transistors are also doubtful after many years of stress.
Don't buy Exicons or any semiconductors on Ebay, particularly from HK traders. If there are difficulties buying EXICON brand direct from Profusion on the net, go to Magnatec and get the same parts branded ALFET. The prices are better when buying from the distributor this way, at least.
Farnell/Newark/Element14/CPC also market ALFET but the premium price they ask in my area makes them unviable. YMMV
Counterfeit Transistors
Suitable Magnatec part numbers are ALF08N16K and ALF08P16K.
Profusion EXICON TO3 parts are ECF10N16 and ECF10P16 . There are higher voltage options that could be used if availability is a problem. Don't be fooled by the apparent discrepancy in brand part numbers. One is derived from the peak maximum current rating and the other is continuous maximum current but they are actually the same chip, if you read the data sheets.
After many years of service my P170 is now starting to act up. Over the weekend the right-hand channel started to produce clicks but is now distorting quite noticeably. I have ordered replacement Mosfets due to discolouration on the pcb around the base of the 2SJ162 . The power supply capacitors look fine and voltages are stable. Does anyone have any other thoughts on a possible cause ?
Ian
Ian
The board will discolour with heat even in a good, working amplifier too. These have minimal heatsinking and will run hot if biased correctly. You can test Mosfets of all types by measuring for a shorted Source-Drain, since this is the most common failure mode. If they check out good, and you will probably have to disconnect the source resistors to measure individual mosfets, I would not remove them yet but look elsewhere, to the voltage amplifier section and the MPSA93/43 support components, including the small caps there. Ideally, you would use a 'scope and sig. generator to compare the +/- driver voltage waveforms which would save a lot of time and guesswork there.
There is no service manual, as you will read here, so only circuit sketches by others are available. This CAD drawing by member Tiefbassubertr, is more detailed, noting that only 1 pair of output Mosfets is shown. Other pairs, with their individual gate and source resistors, are simply in parallel: http://www.diyaudio.com/forums/atta...170-power-amp-c_musical-fidelity-p170_ckt.pdf. There are several sketches reference as P170 but most are of other similar models. See #68 here for more references to P170 mosfet problems.
There is no service manual, as you will read here, so only circuit sketches by others are available. This CAD drawing by member Tiefbassubertr, is more detailed, noting that only 1 pair of output Mosfets is shown. Other pairs, with their individual gate and source resistors, are simply in parallel: http://www.diyaudio.com/forums/atta...170-power-amp-c_musical-fidelity-p170_ckt.pdf. There are several sketches reference as P170 but most are of other similar models. See #68 here for more references to P170 mosfet problems.
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