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Old 9th November 2011, 11:27 AM   #2061
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Quote:
Originally Posted by NED1955 View Post
Hi to everyone,

...how significant is the sound difference with MJ15003's or as I seen elsewhere 2N3773 transistors? I thought I'd get opinions before I spend even more money.
Cheers
I can't comment on the 2N3773 as I haven't tried it but the improvement from changing from the 2N3055 to the MJ15003 is substantial. The bass becomes firmer and the treble/midrange becomes cleaner and more focussed. It is one of the best upgrades I ever made to my JLH.

Tim
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Old 9th November 2011, 12:45 PM   #2062
AndrewT is offline AndrewT  Scotland
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I would guess that a part (maybe a large part) of that sound quality improvement comes from a lower variation in Tj as music signal varies.
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regards Andrew T.
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Old 9th November 2011, 01:31 PM   #2063
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Tim, do you know a retail supplier for the MJ's? They're available from RS and Farnell but they're trade only companies.

Andrew, one factor I've picked up on is the difference in the thermal resistance of the junction to case between transistors. The datasheets quote 1.5 deg C/W for the 2N3055 and 0.7 deg C/W for the MJ15003. From my heatsink calculations that will make a difference of 10 deg C at the junction even with my low voltage version of the amp.

Regards Ned
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Old 9th November 2011, 02:33 PM   #2064
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Default MJ15003

Ned,

CPC sell them...

--|MJ15003|TRANSISTOR, NPN, TO-3 | CPC

Tim.
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Old 9th November 2011, 04:22 PM   #2065
Bone is offline Bone  United Kingdom
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FYI RS, Farnell and CPC will accept orders on line from anyone.
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Old 9th November 2011, 05:48 PM   #2066
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Originally Posted by Bone View Post
FYI RS, Farnell and CPC will accept orders on line from anyone.
I didn't realise that about RS. Useful to know. Farnell need a minimum order of £20.
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Old 9th November 2011, 07:06 PM   #2067
Zeta4 is offline Zeta4  United Kingdom
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Hi
Just seen this thread. Built a a pair of these JLH amps for a friend some years
ago. I used Sanken 2SC2922s for the o/p devices as they did not suffer from
beta droop. Dont know if you can still get these.

Other than the o/p devices the rest of the circuit was as JLH designed it and didnt oscillate or do anything funny. Power supply used gyrator like regulators. Sounded very nice at the time.
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Old 10th November 2011, 06:42 AM   #2068
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Quote:
Originally Posted by Zeta4 View Post
Hi
Just seen this thread. Built a a pair of these JLH amps for a friend some years
ago. I used Sanken 2SC2922s for the o/p devices as they did not suffer from
beta droop. Dont know if you can still get these.

Other than the o/p devices the rest of the circuit was as JLH designed it and didnt oscillate or do anything funny. Power supply used gyrator like regulators. Sounded very nice at the time.
Those 2SC2922's look like very nice devices. They are "quicker" devices and the Cob = 250pF, 4 times less than MJ15003. I would have been concerned about oscillation but you say they were fine. I'm sure they will show a much better slew rate than the MJ's on a square wave input. Don't know if one would hear an improvement but it could as the Toshiba I used on the input made a difference with the "attack" of a note. Pianno and strings are just super. So maybe the Sankens can do the same.
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Old 10th November 2011, 12:57 PM   #2069
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2SC5200 Cob is a mere 200pF. Cheap and easy to find...
TRANS NPN 250V 17A TO264 2SC5200/FJL4315 Fairchild Semiconductor Datasheet
TRANS NPN 250V 17A TO3P 2SC5242/FJL4313 Fairchild Semiconductor Datasheet
TRANS NPN 250V 17A TO220AB FJP5200 Fairchild Semiconductor Datasheet

Last edited by kenpeter; 10th November 2011 at 01:10 PM.
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Old 10th November 2011, 01:38 PM   #2070
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There's a lower gain (Beta 55 min) part marked with an "R"
There's a higher gain (Beta 80 min) part marked with an "O"

Lower gain choice might be closer to a drop-in for 2n3055?

I would still plan ahead for reducing the drive current.
Higher gain and less droop isn't going to need so much...
If you adjust bias, then no harm in the higher gain part...

Last edited by kenpeter; 10th November 2011 at 01:47 PM.
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