Krell KSA 50 pcb - Page 844 - diyAudio
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Old 16th February 2013, 05:33 PM   #8431
henryve is offline henryve  South Africa
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Can it be done? Yes.

Do I think it is a good idea? Nope.

Just bias when everything is not quite in the case. Leave some room and once biased, close it up.
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Old 17th February 2013, 02:52 PM   #8432
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Does anyone have the diy pcb's for the Krell 50 clone? pm me thanks
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Old 17th February 2013, 03:08 PM   #8433
bcmbob is offline bcmbob  United States
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Don't know if you prefer not to deal with eBay vendors, but I did a search yesterday and found the following.

High Power Pure Class A Amplifier PCB KSA50 | eBay

New DIY Class A KSA50 150W Mono Amplifier Board | eBay
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Old 17th February 2013, 03:27 PM   #8434
Arick is offline Arick  Canada
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Quote:
Originally Posted by bcmbob View Post
Don't know if you prefer not to deal with eBay vendors, but I did a search yesterday and found the following.

High Power Pure Class A Amplifier PCB KSA50 | eBay

New DIY Class A KSA50 150W Mono Amplifier Board | eBay
I have purchase the PCB of the first link, the quality is quite good. For more info go to the following link, one of us built his KSA-100 clone with these PCB's.
Eric

http://www.diyaudio.com/forums/solid...-new-post.html
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Old 4th March 2013, 09:16 AM   #8435
henryve is offline henryve  South Africa
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Stupid question.

I am trying to bias this sucker. Do one need to attach a load when biasing the outputs? All my voltages looks OK up to the point after the the drivers. I start off biasing with 520mV on the driver output, but when I measure the voltage over Re, I never get more than around 150mV, no matter how much I open the trimmer.
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Old 4th March 2013, 09:18 AM   #8436
AndrewT is offline AndrewT  Scotland
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set the bias with the input shorted and with the output open.
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Old 4th March 2013, 09:46 AM   #8437
henryve is offline henryve  South Africa
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Thanks Andrew. Have done all that. Beginner's mistake. I forgot to remove the 100W bulb tester from the circuit.
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Old 4th March 2013, 10:10 AM   #8438
henryve is offline henryve  South Africa
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Nice. Now my fuse has popped. I suppose a single standard 3A fuse is not good enough for this beast. I will have to get some stronger fuses. No chance of getting a T type 5A fuse in this town, so I will go for a normal 8A fuse or such.
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Old 4th March 2013, 01:06 PM   #8439
henryve is offline henryve  South Africa
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OK, my left hand channel seems to work perfectly. I biased it to 325mV on Re, and heatsink temps seem fair since the Ta = 36 deg C here at the moment (16h00). I also checked the voltages of Re 1 to 6 and all the voltages are 325mV. The offset is 0.5mV. BTW, Re = .5R.

The right hand channel is not so fine. I can't get it to bias. Also, the voltages on the driver output seems strange so I will have some debugging to do. I get 550mV on the +ve drive while I get -660mV on the -ve drive but with on offset on the FB point of 2mV.
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Old 4th March 2013, 07:50 PM   #8440
henryve is offline henryve  South Africa
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Found my problem. Forgot to solder the output transistors on the bottom layer of the negative output board.

However, this side doesn't seem to be matched so well as the left hand channel. Some of my transistors pull slightly more than the other.

Right Hand side +ve outputs:
Re1 = 303mV
Re2 = 310mV
Re3 = 333mV

Right Hand side -ve outputs:
Re4 = 312mV
Re5 = 320mV
Re6 = 322mV

Should I be worried? Also, my sinks takes a long time to get hot enough so that I can just hold my hands on them for 20 secs. Is this normal for the KSA50 clone?

Last edited by henryve; 4th March 2013 at 07:52 PM.
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