ka-6000 and kt-7000 in tha house, time to restore

bktheking

Gitter Done!
I love old school SS, it's when it was cool, hand made and solid.

I have my work cut out for me, the amp has been through some destruction- 2 of the to-3 outputs and 2 of the smaller outputs have been replaced. I'm going to clean it and do all the lytics in it, one has already blown up and spewed goo inside the amp.

The tuner needs work, I suspect the stereo bulb is burnt cause the needle never gets to the center, I read that the bulb serves as a trigger for the stereo circuit. I will get to it later, the dial glass needs some tlc, it appears to have split or peeled away.

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I have one of these. Sounded wonderful when i played it for the 2 weeks i did back in 2010 before i started a recap with my friend Will (sir.byrd)

But it got half recapped. Still need to locate (or more than likely stuff) the really big coke can power cap. Also have to install the 4 transistors that are usually known for making the amp to go noisy so.

When mine was operational it sounded really good and had great sound! Good luck! Theirs alot of lytics in that amp and lots of point-to-point wiring underneath.
 
They should, they were built when SS was when it sounded best IMO. It may not be a "powerhouse" but who need 800 watts of power for listening to shit in a garage or basement.

I'm thinking the 100V 4000uf cap will become a coffin to house a much smaller 4700uf 100v cap.

The small transistors under the shield. The heatsink paste and different "look" and part number is a dead give away for replacement.

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Replacement output, something smoked it!

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A fine example of "haven't got the right value resistors so lets be cheap and cobble up a rats nest of shit" -think this is bad, you should see the solder work I have to fix! That coupling cap or whatever it is isn't even sitting on the board!


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Underside with some funky smoke patterns, did a cap blow and was replaced??? Other units show the same thing.

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Could you take a picture of the back of this board? There are 2 wires that are soldered to the back traces of this board and mine were desoldered so that i could replace the capacitors and the 4 noisey transistors that go bad on this board.
 
Give me a sec, outside taking a break. I replaced the 10k and 33ohm resistor, got rid of that double up crap, although it works looks amateur.
 
2240's done and all but 5 caps replaced, recapping this board is a delicate job. Resistors were replaced to clean up the left side of the board.


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Removed the leaking cap and started cleaning it up inside.

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2240's done and all but 5 caps replaced, recapping this board is a delicate job. Resistors were replaced to clean up the left side of the board.


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Removed the leaking cap and started cleaning it up inside.

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Did you ever find out what caused that carbon track in between the caps?Looks all original but i don't see anything burned up.....:scratch2:
 
So far i've redone 4 of the big caps and can't find a blown component. I cut 3 open and soldered in the caps, I left one as is and just ran it underneath. I fired it up for the first time tonight first on the dim bulb then on full power, no smoke thank god :banana:. Dead silent and sounds magnificent. I'll post some pics of the cap job tomorrow, i've been at it since this afternoon.
 
OK so now it's time to do the center voltage and bias. After reading umpteen posts and looking at the 4000 service manual this is what i've come with:

Potentiometers VR903/left channel and VR904/right channel adjust the “center voltage”.

Center voltage according to the schematic should be 43V, each channel should be set by putting the meter on the + of the 3300uf cap and ground.

Potentiometers VR905/left channel and VR906/right channel adjust the bias.

Bias should be 23.5 mv and taken from R172 and R271.

I tried reading the procedure on how to set it using "jack a" but it was written in Japanese and converted to English, it makes no sense. I'm afraid of "jack a", looks like something to cause smoke!
 
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The bias procedure out of the manual is a little messed up, maybe the 4000 and 6000 procedure isn't the same but I can't see that. Center voltage at 43V puts current close to 100ma and ran the heat sinks at 150F. On another thread 100ma was mentioned and 50ma was corrected, voltage somewhere is wrong. I think something somewhere is wrong with the bias setup.


Here's what I did to set it properly:

I ignored the 43V part and just went to setting the bias to 50ma across each resistor. I used the inside pots "vr905 and vr906" to get it close to 50ma and then used the outer pots "vr903 and vr904" to fine tune the current to get it spot on 50ma. Now the heatsinks are sitting at 110F after an hour of constant playing.

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To do the caps this is what I did.

1. Using a dremel cut off disc I cut the cap open in the center of where the holder sat.

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2. Remove the inside of the cap and cut the leads off. Remove the lead going around the lugs as best as you can.

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3. Cut two short pieces of solid core wire, I used 18 gauge. Strip the leads long enough so you can wrap them under the lug. The lug's are aluminum, make sure the wire wraps back around itself in a loop so you can solder it together.

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