Replacement for Sanken A1186/C2837 - diyAudio
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Old 31st July 2009, 05:09 PM   #1
CBRworm is offline CBRworm  United States
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Default Replacement for Sanken A1186/C2837

I am working on an amplifier which has a bad channel. The amplifier has been repaired in the past (not by me) - about 11 years ago. The good channel has two pairs of A1186/C2837 (original). The bad channel has 2 original A1186, 1 ECG36, and one significantly smaller transistor labelled 2sc2837, but most of the ink has wiped away.

The owner said he accidentaly shorted the outputs for a second and the sound has been distorted since.

It appears that the replacement transistors have failed, I have not gotten to the drivers yet. I have found these transistors listed on Sankens web site, but have not been able to figure out if they are still in production or where to get real ones.

The amplifier is a 22 year old Onkyo Integra A8087. I would not mind replacing them with on-semi replacements if there is something suitable in a TO-3P package.

are there any proven replacement transistor pairs?

Thanks
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Old 31st July 2009, 06:03 PM   #2
CBRworm is offline CBRworm  United States
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is MCM a reliable source?
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Old 31st July 2009, 06:21 PM   #3
jaycee is offline jaycee  United Kingdom
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MCM is reliable - they are part of Farnell. The 1186/2837 is still in production according to Sanken.

OnSemi have NJW0281/NJW0302 in TO-3P packages but they are not as fast or low Cob as the Sankens. They might work acceptably, but they might need compensation adjustments to the rest of the circuit.
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Old 31st July 2009, 08:49 PM   #4
CBRworm is offline CBRworm  United States
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Ok, I will order them from MCM - worst case if they look suspicious I will do some more searching.
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Old 31st July 2009, 09:26 PM   #5
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CBRworm,
the A1186/C2837 is really nice. Could you post a picture of them later, please?
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Old 31st July 2009, 09:32 PM   #6
CBRworm is offline CBRworm  United States
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Yes - once they show up I can do that.
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Old 31st July 2009, 10:12 PM   #7
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CBRworm,
thanks, counterfeiting is prevalent nowadays.
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Old 1st August 2009, 04:54 AM   #8
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These Sanken power transistors have high a Ft and good 100W/60pF Cob ratio.

The 100W NPN Sanken 2SC2837 Y Rank has hfe= 90-180, Ft=70Mhz, and a low COB=60pF

The 100W PNP Sanken 2SA1186 Y Rank has hfe= 90-180, Ft=60Mhz, and a low COB=100pF

I use 1-2 pairs for low wattage Class A amps.

I use 8-16 pairs for high current Class A amps.
Optimal Class-A transistion to Class-AB biasing requires ~23mv across each emitter resistor. A high current amp with optimal bias requires many pairs. The low 60-100pF Cob, vs. 400-500pF Cob for most 200 Watt transistors, allows paralleling many of these Sankens with a normal VAS stage.
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Old 7th August 2009, 06:46 PM   #9
CBRworm is offline CBRworm  United States
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Here are the pictures as promised.

I hope they are real - the lettering doesn't look great - but they came from MCM.

Hmmm.. Pictures have to be really small.
Attached Images
File Type: jpg onka8087 001a.jpg (53.8 KB, 377 views)
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Old 7th August 2009, 08:16 PM   #10
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there are some new bjt's available, e. g. "ST" and "ON"
I have listed the most populare types - go to
bipolar (bjt) transistor families for audio power output stages
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