KA-8006 recap - a few issues

iamthejeff

Active Member
I just finished a full recap of a KA-8006 and I'm happy to say it went perfectly. I also replaced the relay as it was causing some audio cutouts. DC offset measures 2 mV and 16 mV.

The amp works great now but I noticed that R1 and perhaps R2 as well on the power supply board are extremely hot. So hot that I can feel the heat rising on my face simply looking down into the unit with the top off.

R1 looks a little toasty, and actually matches this picture posted by another AK member a while back:

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Is it worth looking into fixing this? Can it be fixed? I worry about the heat buildup once I put the top on.

As an aside, I also want to measure the bias just to make sure it's correct. I did a search and found a few other posts on the topic but no clear answers.

Forgive me for being an electronics newbie, but can somebody point me to the correct pins on the circuit board that I need to hook my voltmeter up to?

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Replace all the electrolytic caps on that board...while the old caps are off, scrape all the old crusty assembly glue off. When ordering parts, don't forget that Ck4 is a bipolar cap. Replace the overheated resistors with 2 or 3W Panasonic metal film jobs (both Mouser and Digikey sell them). Mount them above the board like the originals, so they can breathe.

To adjust the bias, connect a minigrabber lead to Pin 8 (+) and Pin 5 (-) of the driver board and adjust for 30mV (dunno why the manual has the other goofy procedure, but measuring voltage at the pins I name is much safer than fooling around with a current measurement)..
 
Thanks so much! I did recap the *whole* unit already with good quality caps, so the bulk of it is done. I didn't notice the single bipolar cap, so I had to make a 2nd order haha. But it's all good now.

I'm glad that the two resistors are extremely easy to access.

While I am at it, is it worth replacing the output transistors? The unit sounds really good right now, and I don't know how likely transistors are to fail during normal operation conditions. Are they fairly reliable? I mostly want to *really* extend the life of this thing. Make it last another 40 years if possible :D
 
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