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Old 12th January 2013, 01:30 AM   #2531
spurlte is offline spurlte  United States
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All I need to finish my KSA-100 are a set of fan type heat sinks. Even FIX is out of them. I found these on ebay but wonder if they are big enough.
1pcs Aluminum Heatsink for Amplifier ?Fan Type 300mmx93mmx63mm | eBay. Suggests anyone?
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Old 12th January 2013, 06:14 AM   #2532
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[/QUOTE]
1pcs Aluminum Heatsink for Amplifier ?Fan Type 300mmx93mmx63mm | eBay. Suggests anyone?[/QUOTE]

Looking at this heatsink...
It`s center stem is too thin for proper heat conduction of a pure class A as a Krell KSA100.
It`s a poor copy of the original heatsink.
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Old 12th January 2013, 07:57 AM   #2533
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Quote:
Originally Posted by spurlte View Post
have you had luck in locating your transistors? How far are you with the KSA-100? Where are you going to get your output heatsink?
Single transistor which I found Toshiba 2SC2238 and 2SA968. On Ebay I do not inspire confidence in buying from China and Hong Kong.
I miss filtering capacitors are not decided on its purchase and I are missing a few pieces. Krell finish in 4 months.
Build two monoblocks in class AB and if you are satisfied with the sound, like in about 1 year 2 monoblocks class A building with passive cooling.
Toshiba 2SC2238, 2SA968 transistors original find, U.S. ?
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Old 11th February 2013, 02:25 PM   #2534
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I've built 9 channels for LCR tri-amped speakers using this thread. After 6 month of running fine, one of the channels started to die every half an hour or so. The reason is failing Q3 (negative rail LTP "input" transistor, the left bottom 2SA970 on the schematics). Here is what I see after failure:
1) Dead transistor measures with ohmmeter fine.
2) Amplifier output is close to the negative rail (-45V).
3) Q3/Q1 base are about - 5V
4) After replacing the transistor everything seems fine.

Here is what I've done except just replacing transistors about 7 times already:
1) Put DC blocking capacitor on the input
2) Put 2 by 3 diodes between Q1/Q3 and Q2/Q4 bases in opposite direction to protest the Q1, Q2, Q3, Q4 EB junctions from reverse voltage

I have separate power supplies for LTPs and VAS + output. The first one is stabilized 60V shared with the other 3 channels on the same chassis. The second one for this particular channel is 45V. The input is from a crossover on the same chassis.

What can cause it?

Last edited by stolbovoy; 11th February 2013 at 02:28 PM.
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Old 27th February 2013, 10:56 AM   #2535
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Iím thinking to double output transistor amount.
I have drivers MJE15032/33 and Iím planning to use 8 pairs MJ15024/25 for output.
So one MJE15032/33 will drive 8 pcs MJ15024/25.
Is there something I should be known or take special care?
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Old 27th February 2013, 11:06 AM   #2536
AndrewT is offline AndrewT  Scotland
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The ksa100 already has two pairs of drivers. One driver pair drives two output pairs.
__________________
regards Andrew T.
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Old 27th February 2013, 03:21 PM   #2537
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I mean to use four output transistors behind for one driver transistor.
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Old 28th February 2013, 06:54 AM   #2538
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Feel free to take it to the extreme if you like walking on the edge.
twice the load on the driver stage plus cutting it`s ability by 50%.
it`s a sure recipe for overload and circuit failure. but hey, it`s your money...
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Old 28th February 2013, 08:21 AM   #2539
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Thanks for your comments. So I may stay with original amount.
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Old 28th February 2013, 02:43 PM   #2540
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Quote:
Originally Posted by BenY View Post
Feel free to take it to the extreme if you like walking on the edge.
twice the load on the driver stage plus cutting it`s ability by 50%.
it`s a sure recipe for overload and circuit failure. but hey, it`s your money...
Why? What if he will keep the total bias the same? Even if the total bias current will be twice of original will it put the drivers outside of SOA?
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