Musical Fidelity P270-2 output devices? - diyAudio
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Old 15th February 2009, 11:43 AM   #1
kenneth is offline kenneth  Sweden
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Wink Musical Fidelity P270-2 output devices?

I have bought a secondhand Musical Fidelity P270-2 power amp recently. The amp works fine but someone seems to have replaced the output devices to K1058 and J162 types. The repair seems kind of amateurish so i would be very happy if someone could confirm that these are the correct output devices (or equivalents).

Thanks,

Kenneth
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Old 15th February 2009, 12:18 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
the 2sk1058/j162 are Lateral mosFETs by Renesas.
They are the modern equivalent to 2sk135/j50 by Hitachi.
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Old 15th February 2009, 12:22 PM   #3
jaycee is offline jaycee  United Kingdom
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The original amps used the 2SK135/2SJ50 pairs from Hitachi. At least that's what the schematics indicate.

MF had the annoying habit of soldering a wire directly to the MOSFET case, rather than using a proper terminal under one of the screws, so if that's what's under the hood of yours, whoever repaired it has only done what MF themselves did!!
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Old 15th February 2009, 07:18 PM   #4
kenneth is offline kenneth  Sweden
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No there are no wire to the mosfets cases. But i am curious why there are ferrite beads attached to the right legs of the mosfets?
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Old 15th February 2009, 11:57 PM   #5
jaycee is offline jaycee  United Kingdom
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hmm.. bit odd that they have swapped TO-3 cased mosfets for flatpack ones! Unless of course, MF updated the design.

The ferrite should be on the gate lead (pin 1) to help prevent oscillation. If it is on pin 3, it's in the wrong place.

Does it look like there are supposed to be TO-3 cased devices in there? It'll be quite obvious from the drill holes on the heatsink. If it's supposed to be TO-3 devices I would consider putting them back as TO-3's have better thermal dissipation than the flatpacks.
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Old 16th February 2009, 08:28 AM   #6
AndrewT is offline AndrewT  Scotland
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would a ferrite on the gate lead increase or decrease the risk of oscillation?
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Old 16th February 2009, 10:23 AM   #7
kenneth is offline kenneth  Sweden
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Here are a picture of the modification.
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Old 16th February 2009, 10:45 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
this amp may have been fitted with 2sj81/2/3 & 2sk225/6/7.
These are two bolt fixing flatpacks, with very good Rth c-s. Probably better than To3.
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Old 16th February 2009, 11:02 AM   #9
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Original P270, 3 pairs of J82/K226 per side.
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Old 16th February 2009, 12:57 PM   #10
AMV8 is offline AMV8  United Kingdom
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Hi

As Jacco states the original P270's Original P270, "3 pairs of J82/K226 per side".

The original P270 ran very hot and the output devices burned out on some amps and were replaced. The Mk 2 version of the P270 had a lower bias and ran cooler.

I am guessing that you have an early amp with replaced output devices. I have P270 with original devices and one with replaced output devices. They sound the same although the original parts could accept slightly more current.

The beads on one leg of the output device were meant to stop oscillation. I have no idea whether they were really necessary or not - but they were on the original factory supplied amps.

Don
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