Tips and pics on my KA-8006 restore and future restores

saabracer23

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So I have been into audio for some time, since I was about 10 and I'm 32 now. I purchased my first powered subwoofer when I was 12 with Christmas money and I was lost from there. I've owned a lot of gear but have recently decided to simplify. I've been having issues with my "newer gear" with their bells and whistles. I decided to ge back to old school. I'm dropping the surround and going back to stereo. My start up system will consist of Kef reference 105.1 speakers, velodyne HGS-15 subwoofer, Philips GA-312 TT. For now power will come from a Kenwood KA-8006, as soon as I finish restoring it, will then be a model 600.

The KA-8006 was given to me for free. It works perfectly, everything about it works excellent. I want to completely restore it. I figure it will be good practice to do this guy before I move onto the Model 600. I'm a DIYer at heart and I've done a lot of PCB work and have many tools knowledge to feel confident in this. I'm not a complete newb. I will say this will be my first time completely tearing down a vintage amp and restoring it.

So my questions are, what are the things I'll want to replace? All of the electrolytic capacitors of course (including the 15,000 uF ones). I've seen some people increase the wattage values of the resistors on the power supply board. I see there are many that replace the relay, I'm guessing that would be a good idea? I've also read in some of the model 600 rebuild threads that people will replace parts that are known to be troublesome just to eliminate them as issues in the future. Are there any parts in the KA-8006 that that are that way?

Basically I want to know what exactly are all the pieces I should change out to complete this restore. I appreciate everyone's help!













Dan
 
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So I was talking to some folks over at diyaudio and they strongly suggest I increase the filter cap capacitance. It was suggested I could go up 50% with zero issue to the transformer or rectifiers. So go from 30,000 uF to 45,000 uF.

Thoughts?

Dan
 
The rectifiers can likely deal with it OK, but the power switch will be unhappy. It is probably overworked on this model in any case.

Additionally, you may not have as many choices as you suppose, depending on the physical size of your current caps and their electrical connection style (probably solder lug). I suspect that the original caps are 50mm diameter. If so, this is a good replacement and probably as large as I'd want to go with that unit. If it fits, you'll need to add ring terminals to your current wiring for attachment to the cap.
 
The rectifiers can likely deal with it OK, but the power switch will be unhappy. It is probably overworked on this model in any case.

Additionally, you may not have as many choices as you suppose, depending on the physical size of your current caps and their electrical connection style (probably solder lug). I suspect that the original caps are 50mm diameter. If so, this is a good replacement and probably as large as I'd want to go with that unit. If it fits, you'll need to add ring terminals to your current wiring for attachment to the cap.

That's good to hear the rectifiers should be ok. The power switch was another concern of mine, but did not know it should be that big of a concern. I have seen your work so I'll take your word as gold. Why is it you think the power switch is already stressed in this model? I ask as I thought Kenwood made this and others in this series like tanks, overkill.

I plan on pulling the cover off and using my digital calipers to measure the filter caps. Thanks for the link though. The caps in the 18,000 uF size a very limited in selection. I'd probably be better off going back to a 15,000 uF. Is there any possibility that there would be any positive benefits from going to a larger filter cap? Only 6,000 uF total increase. I had planned on going with a screw terminal like the Epcos and doing a the appropriate steps to make hookup possible.

I also plan on using 2.2 uF poly caps as bypass caps on the filter caps.

What are the general thoughts on replacing all of the electrolytic caps in the preamp circuit with either poly, film, mylar, or???

It was suggested to me at diyaudio forums. Would I be wasting my time? If I don't I would just use Elna Silmic II caps in the preamp section.

Also, what is the general thought about this amp? Is it loved or hated? I love my 600 but this one will be used in a secondary system.

Thanks
Dan
 
Also, thoughts on replacing the opamp in the phono section? I've read the phono preamp in the KA-8006 is kinda the weak point in the amp. So it was suggested by a well known, well skilled member at diyaudio to do it.

"The opamp in the phono section is an RC4558T -- one of the earliest dual opamps. You might try plugging in an LM4562 or other low noise dual bipolar opamp."

But like every other forum the idea was both criticized and praised.

Dan
 
That's good to hear the rectifiers should be ok. The power switch was another concern of mine, but did not know it should be that big of a concern. I have seen your work so I'll take your word as gold. Why is it you think the power switch is already stressed in this model? I ask as I thought Kenwood made this and others in this series like tanks, overkill.
To a point. But anytime you're charging 30,000uf or more of capacitance with no provisions for a soft-start, longevity of power switches is always an issue. But E-Switch makes a replacement that'll fit right in there (I'm pretty sure).
I plan on pulling the cover off and using my digital calipers to measure the filter caps. Thanks for the link though. The caps in the 18,000 uF size a very limited in selection. I'd probably be better off going back to a 15,000 uF. Is there any possibility that there would be any positive benefits from going to a larger filter cap? Only 6,000 uF total increase. I had planned on going with a screw terminal like the Epcos and doing a the appropriate steps to make hookup possible.
Not much to gain, but I recommended the United Chemi-Cob 18K cap because a) you seemed to want a bit more capacitance, which is reasonable, and b) because the UCC caps are very good and reasonable priced, and have screw terminals, which are great as there's no soldering directly to the cap, and c) if your stock caps are 50mm or so, then these are some of the best that will fit in there like they grew there.
What are the general thoughts on replacing all of the electrolytic caps in the preamp circuit with either poly, film, mylar, or??? It was suggested to me at diyaudio forums. Would I be wasting my time? If I don't I would just use Elna Silmic II caps in the preamp section.
Up to about 4.7uf, this is feasible if there's enough room on the PC board. Anything larger and it gets real difficult.
Also, what is the general thought about this amp? Is it loved or hated? I love my 600 but this one will be used in a secondary system.
Nice amp, worth the effort. But your opinion is the only one that matters.
Also, thoughts on replacing the opamp in the phono section? I've read the phono preamp in the KA-8006 is kinda the weak point in the amp. So it was suggested by a well known, well skilled member at diyaudio to do it.

"The opamp in the phono section is an RC4558T -- one of the earliest dual opamps. You might try plugging in an LM4562 or other low noise dual bipolar opamp."
The 4558 does a decent job, and there are gotchas involved with popping in modern fast opamps in vintage gear. Some newer opamps are picky about board layout, some not (I use the OPA2132 a lot, as it doesn't seem to be terribly picky about layout, but I'd admit that the LM4562 looks decent on paper). In any event, I'd not be sweating the phono opamp till everything else was done and working.

One thing not mentioned...good idea to get rid of the stock bias trimpot and replace with a decent Bourns job. There's also a couple of 2SC1451's that gotta go.
 
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To a point. But anytime you're charging 30,000uf or more of capacitance with no provisions for a soft-start, longevity of power switches is always an issue. But E-Switch makes a replacement that'll fit right in there (I'm pretty sure).Not much to gain, but I recommended the United Chemi-Cob 18K cap because a) you seemed to want a bit more capacitance, which is reasonable, and b) because the UCC caps are very good and reasonable priced, and have screw terminals, which are great as there's no soldering directly to the cap, and c) if your stock caps are 50mm or so, then these are some of the best that will fit in there like they grew there.Up to about 4.7uf, this is feasible if there's enough room on the PC board. Anything larger and it gets real difficult. Nice amp, worth the effort. But your opinion is the only one that matters.

I want to say thank you very much to you and to all at this forum. The people at this forum and techtalk ore some of the nicest folks I know. I put a thread up at diyaudio about this very subject and was told that I was a troll and I'm completely wasting my time and money replacing 40 year old caps as they are completely fine. Some are very rude there, it got ugly.

Thanks again. I'll be posting progress and thoughts as I go

Dan
 
Couple of assholes...ignore them. I did add my 2¢ worth at the end of the thread.

But I'll reiterate here a bit of what I said there. On most of these vintage pieces, it's entirely too easy to destroy PC board traces, so a decent temp-controlled soldering iron is needed. Solder wick is also mandatory...I use this stuff: http://my.mouser.com/ProductDetail/Plato/1811-25F/?qs=sGAEpiMZZMuzEnlwMwYUNhHpn9jErgQEl0vUG6XZAto= A solder sucker is a nice thing to have, and handy, but you can get by without it at the expense of using more wick (and solder joints that have been hit with the sucker usually have to be followed up with the wick anyway). Still...a good solder sucker is an essential tool if you do this much.

A dab of paste flux both when desoldering AND soldering helps a lot. Here's a short bit I wrote about desoldering a while back...it might help to save a few PC board traces: http://www.audiokarma.org/forums/showpost.php?p=2922066&postcount=21

When ready to solder a new part in place, a small dab of paste flux helps the heat to disperse evenly, and thus the solder flows evenly. Rookies can make pro-looking connections with the help of a dab of paste (and I'm no rookie, but I use a dab of paste flux on just about every solder joint I make). It can get messy, but a Q-Tip and some alcohol or acetone will clean it up. This stuff works great: http://my.mouser.com/ProductDetail/MG-Chemicals/8341-10ML/?qs=sGAEpiMZZMtm36YkO3Igk%2b0%2bVw8aUsIm

RatShack also sells some, but in the round plastic container as they sell it, it has to be stored in the fridge when you're not using it: http://www.radioshack.com/2-oz-non-...-paste-flux/6400022.html#q=Paste+flux&start=2 The syringe doesn't have that drawback.
 
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Couple of assholes...ignore them. I did add my 2¢ worth at the end of the thread.

But I'll reiterate here a bit of what I said there. On most of these vintage pieces, it's entirely too easy to destroy PC board traces, so a decent temp-controlled soldering iron is needed. Solder wick is also mandatory...I use this stuff: http://my.mouser.com/ProductDetail/Plato/1811-25F/?qs=sGAEpiMZZMuzEnlwMwYUNhHpn9jErgQEl0vUG6XZAto= A solder sucker is a nice thing to have, and handy, but you can get by without it at the expense of using more wick (and solder joints that have been hit with the sucker usually have to be followed up with the wick anyway). Still...a good solder sucker is an essential tool if you do this much.

A dab of paste flux both when desoldering AND soldering helps a lot. Here's a short bit I wrote about desoldering a while back...it might help to save a few PC board traces: http://www.audiokarma.org/forums/showpost.php?p=2922066&postcount=21

When ready to solder a new part in place, a small dab of paste flux helps the heat to disperse evenly, and thus the solder flows evenly. Rookies can make pro-looking connections with the help of a dab of paste (and I'm no rookie, but I use a dab of paste flux on just about every solder joint I make). It can get messy, but a Q-Tip and some alcohol or acetone will clean it up. This stuff works great: http://my.mouser.com/ProductDetail/MG-Chemicals/8341-10ML/?qs=sGAEpiMZZMtm36YkO3Igk%2b0%2bVw8aUsIm

RatShack also sells some, but in the round plastic container as they sell it, it has to be stored in the fridge when you're not using it: http://www.radioshack.com/2-oz-non-...-paste-flux/6400022.html#q=Paste+flux&start=2 The syringe doesn't have that drawback.

Cool thanks I read that over there, I appreciate that. I have quite a bit of soldering and de soldering in my past. I currently have a Xytronic iron with a digital temp readout. Is there specific temp I should use for vintage gear?

I used to have a solder sucker but hated it. It was one of the one where you push down the pluger and release it to suck. It would get clogged and it wasn't very good. I'm sure an electronic one is way better. Let's just say I now have about 10-15 rolls of wick. That stuff is great.

I can honestly say I have never used flux with the exception of copper plumbing. The guy that owns the local electronics store here said I shouldnt need it as the solder that I was using has flux in the core. I've never had an issue, but I guess I should pick some up.

Thanks for your help. Any suggestions for me? I noticed you commented on the transistors. Anything from my list you think I should forget about doing to the amp?

Thanks again,
Dan
 
The main transistor in question is labeled 2SC1451. I was told that one was troublesome. That and I might as well just replace all that I can source while I have it open. Was I given bad info? Should I just leave them be? I popped open my amp so I could take pics.







Dan
 
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See post 8 above about the 2SC1451. If Echowars says they gotta go, then they gotta go.

He also mentions the trimmer which is the part labeled VR1. These old carbon trimmers make it hard to adjust anything properly so you'll wanna replace those with some good Bourns multi-turn trimmers that you can really dial in. There are some precautions to replacing the trimmers you need to be aware of though, which others can explain better than I, so make sure you ask about that specifically before doing anything to them.

I went over and read what was said in the diyaudio forum and it just makes me appreciate this place that much more. We can all have differences in opinion about replacing parts, but one thing that can't be argued is that some of the parts that went in to these old things have a lifespan, just as simple as that. I have hard time understanding why anyone would have issue with you replacing capacitors of that age. My personal opinion..If I have a unit of that age that's worthy of restoration all electrolytic caps go. Possible exceptions are the large filter caps, which can become cost prohibitive, and rarely caps in the tuner section of some receivers.

One other little tidbit, I don't know the history of the unit you are working on obviously, but anytime I see a shop sticker (from the photo above) on the back indicating it may have been worked on... I can't trust entirely that all parts are original. Just something to keep in mind when replacing parts. Cheers and good luck to you.
 
Cool thanks I read that over there, I appreciate that. I have quite a bit of soldering and de soldering in my past. I currently have a Xytronic iron with a digital temp readout. Is there specific temp I should use for vintage gear?
I'm usually set to about 650°F.
I used to have a solder sucker but hated it. It was one of the one where you push down the plunger and release it to suck.
That's how they work. :)
It would get clogged and it wasn't very good.
The classic Soldapullt is a very well-built tool. They do require disassembly and cleaning from time to time...that's the nature of the beast.
I can honestly say I have never used flux with the exception of copper plumbing. The guy that owns the local electronics store here said I shouldnt need it as the solder that I was using has flux in the core. I've never had an issue, but I guess I should pick some up.
The amount of flux in the solder is burned up very quickly. Adding flux to the joint makes a near-perfect solder joint almost automatic, and a small dab on a joint to be desoldered (with wick, as a solder sucker gets jammed up by using paste) helps pull more solder from the joint at lower temperatures, helping to save the precious foil traces.
Thanks for your help. Any suggestions for me? I noticed you commented on the transistors. Anything from my list you think I should forget about doing to the amp?
Get rid of the old electrolytics. My basic selection guide is here. Look for overheated resistors, and replace as necessary.
The main transistor in question is labeled 2SC1451. I was told that one was troublesome. That and I might as well just replace all that I can source while I have it open. Was I given bad info? Should I just leave them be?
The only transistors I'd be replacing outright are the C1451's, Qk1 and Qk2, the protection trans and the relay driver trans, and perhaps the input differential pair transistors at the input of each amp channel (Qe1 and Qe2) with a new high-gain pair.

Suggestions for replacement transistors:

2SC1451 -> 2SC3902T (Mouser)
2SA620 -> 2SA970BL (B&D Enterprises, need a dozen or so to gain-match two pair)
2SC1212A relay driver -> 2SC3902T
2SC1416 detector -> 2SC2240BL (B&D Enterprises)

Yes, the stock bias trimpot needs to get shitcanned. Replacement is Mouser #652-3296P-1-102LF (25-turn Bourns). Will be a bit tricky to install, but should do fine with a bit of creativity.

Somewhere down the line you can attack that phono opamp if you like, but I'd do the rest of the unit before I worried about that.
 
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See post 8 above about the 2SC1451. If Echowars says they gotta go, then they gotta go.

Haha I totally read over that. Oops thanks for pointing that out.

He also mentions the trimmer which is the part labeled VR1. These old carbon trimmers make it hard to adjust anything properly so you'll wanna replace those with some good Bourns multi-turn trimmers that you can really dial in. There are some precautions to replacing the trimmers you need to be aware of though, which others can explain better than I, so make sure you ask about that specifically before doing anything to them.

I was actually planning on replacing them. I've done a lot of reading lately and it seems as though most people do replace them.

I went over and read what was said in the diyaudio forum and it just makes me appreciate this place that much more. We can all have differences in opinion about replacing parts, but one thing that can't be argued is that some of the parts that went in to these old things have a lifespan, just as simple as that. I have hard time understanding why anyone would have issue with you replacing capacitors of that age. My personal opinion..If I have a unit of that age that's worthy of restoration all electrolytic caps go. Possible exceptions are the large filter caps, which can become cost prohibitive, and rarely caps in the tuner section of some receivers.

I haven't come here much in the past, I kind of just joined and left. I'm really glad I found it again. Just like techtalk this place just feels like home if that makes sense. It's very welcoming here and I enjoy coming here. That wasn't the first time I have rude, obnoxious people post in my thread. There are wonderful people there as well. Here, people respect each other. But I agree time to change some parts!


One other little tidbit, I don't know the history of the unit you are working on obviously, but anytime I see a shop sticker (from the photo above) on the back indicating it may have been worked on... I can't trust entirely that all parts are original. Just something to keep in mind when replacing parts. Cheers and good luck to you.

Yes, when I had the amp apart today I noticed that some of the solder joints looked fresher than others. Looks like the mainly belonged to resistors. I haven't been able to place my order for parts yet as more and more things are showing up on my shopping list. To say I'm excited about all this is an understatement!

Dan
 
I'm usually set to about 650°F.That's how they work. :)The classic Soldapullt is a very well-built tool. They do require disassembly and cleaning from time to time...that's the nature of the beast.The amount of flux in the solder is burned up very quickly. Adding flux to the joint makes a near-perfect solder joint almost automatic, and a small dab on a joint to be desoldered (with wick, as a solder sucker gets jammed up by using paste) helps pull more solder from the joint at lower temperatures, helping to save the precious foil traces.Get rid of the old electrolytics. My basic selection guide is here. Look for overheated resistors, and replace as necessary.The only transistors I'd be replacing outright are the C1451's, Qk1 and Qk2, the protection trans and the relay driver trans, and perhaps the input differential pair transistors at the input of each amp channel (Qe1 and Qe2) with a new high-gain pair.

Suggestions for replacement transistors:

2SC1451 -> 2SC3902T (Mouser)
2SA620 -> 2SA970BL (B&D Enterprises, need a dozen or so to gain-match two pair)
2SC1212A relay driver -> 2SC3902T
2SC1416 detector -> 2SC2240BL (B&D Enterprises)

Yes, the stock bias trimpot needs to get shitcanned. Replacement is Mouser #652-3296P-1-102LF (25-turn Bourns). Will be a bit tricky to install, but should do fine with a bit of creativity.

Somewhere down the line you can attack that phono opamp if you like, but I'd do the rest of the unit before I worried about that.

You are just a treasure trove of information. You're an incredible help, I really really appreciate all you've done.

I'm going to make a "complete and final" shopping list and I'll post it here and see what everyone thinks.
 
I've been doing this a while. But FWIW, I've never rebuilt an 8006.

Anyway, you'll need a new speaker relay as well. Almost certainly an MY4-02-DC24. Mouser has 'em.

And if you do not have minigrabber leads for your meter, get 'em: http://www.audiokarma.org/forums/showpost.php?p=2867400&postcount=10

Haha already on my list, you are correct in the model number. I have these leads for my fluke that allow you to screw different ends on. I have the mini grabbers, alligator clips, tiny pin point ends that help eliminate shorts and one other thing that slips my mind. $20 well invested.

Dan
 
What is he general thought on tantalum capacitors. I see there are quite a few in the audio section of this amp and I see some people really dislike them. Is it worth my time to replace them or should I leave them be?

Dan
 
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