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Threshold Cas-2
Threshold Cas-2
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Old 18th February 2014, 12:23 PM   #11
JamesBrennan4 is offline JamesBrennan4  United States
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Original transistors were most likely CAS5, CAS6, CAS8.
Look at CAS1 schematics - CAS5 and CAS6 (could be marked as A5 and A6)
Look at 400A / 4000 schematics - CAS8 and CAS6 (could be marked as A8 and A6)

There have been several threads on recommended replacements for these amplifiers.
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Old 18th February 2014, 01:08 PM   #12
6JohnS is offline 6JohnS  United States
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Thanks for the help and I grateful for everyone steering me in a direction. I am a very analytical guy but I have very little electronics education. I follow instructions well and I have built more than a few amps (mostly tube) in my day. What I am not understanding is why someone doesn't tell me what I asked for, the part numbers for the original transistors or a suitable replacement. I will follow your suggestion in hopes that I can figure it out. Thanks again.
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Old 18th February 2014, 01:53 PM   #13
JamesBrennan4 is offline JamesBrennan4  United States
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Mospec 2N5876/2N5878 or ON MJ21193/MJ21194

The original transistors are marked A5 and A6

I have a CAS2.

I replaced all of the output transistors with ON MJ21193/MJ21194.
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Old 19th February 2014, 12:21 AM   #14
6JohnS is offline 6JohnS  United States
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James, Thank you. That is exactly what I needed. I have already ordered new ones. Would you advise me to replace the power capacitors as well? They have been discharged for at least 15 years. Thank you again for the direct help. John
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Old 19th February 2014, 12:28 AM   #15
JamesBrennan4 is offline JamesBrennan4  United States
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I always have replaced the filter caps with as large a value in capacitance with the same voltage rating that will fit in the space available.

But, using a variac, you could slowly bring up the voltage. Maybe they will not fail, at which point, listening test may confirm need or not need to replace capacitors.
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Old 19th February 2014, 01:10 AM   #16
6JohnS is offline 6JohnS  United States
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I am in this amp for the long haul but I will bring it up slowly and see what happens. The Caps are marked well and shouldn't be too hard to find replacements. I will look into how much they are and if they aren't prohibitively expensive I will replace them all now. I will do a full tear down and a thorough cleaning and perhaps I will get many more good years out of this amp. Thanks again for your and everyone's help and advice. John
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Old 25th December 2018, 04:46 PM   #17
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Hi all,

Sorry to bring this thread back from its graveyard. I have one and i know it old and dont know how many owners has it been through but it is still one good amp. In the future i am planning to power planner speakers. Do you guys know if this amp can handle the low impedance from the planners or maybe martin logan electrostatic speakers.
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Old 25th December 2018, 06:32 PM   #18
Zen Mod is offline Zen Mod  Serbia
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question for Pa
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Old 28th December 2018, 01:07 AM   #19
outfire is offline outfire
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Wonder when will PA shows up
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Old 28th December 2018, 02:35 AM   #20
Zen Mod is offline Zen Mod  Serbia
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well , he and boyz claimed some things long ago , most of them working in your favor

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