KA-8006 Re-cap & Repair Cost

Picked up a garage sale KA-8006 today.
Owner said it wasn't working.

I cleaned it up and sprayed all the pots and selectors.

It looks nice. It powers up, and sounds pretty good, but right channel has a little hum to it and the left channel is noticeably weaker than the right without any hum. This is consistent with a TT to either Phono input and a CD to Aux1 and switching L/R RCA connections so it must be in the amp somewhere?

I don't have much $ into it so far, what would be a ball park cost to have it re-capped and repaired? ( assuming I can find someone to do it)

Thanks
Jim

Very hard to estimate. Tech charges might run around $65 an hour, or they may quote by the job. My advice would be to look for loose ground wires as a first hum source, make sure the power transformer is securely fastened to the chassis, and give the caps a good looking at to see if any are bulging or leaking. There's a 4 channel output/input set of RCA jacks on the back and a Normal/Separate switch. Make sure that switch gets a good cleaning and working back and forth. When you say you sprayed the pots and switches, what did you use and did you work them through their ranges a bunch? Hit the balance knob, speaker selector, phono impedence and separate switches.

Not sure if it works exactly like Preamp Out/Power Amp In switches, but if so, and if you have another amp with preamp Inputs, you can try and determine if the issue lies with the preamp or power amp section. Set the switch to "separate" and then run RCA cables from the Output jacks to the Inputs of the other amp. Use the KA-8006 just as a preamp and see if the quietness and or hum is present in the speakers being driven from the other amp. If so, the issue most likely lies in the preamp section. If, on the other hand, this wiring arrangement clears up the problem, your quietness and hum lie in the power amp section.

If you can learn to do the work yourself, parts might cost $50 or so for a complete recap and replacement of some problem transistors if needed.

Download a Service Manual from hifiengine, get a hold of a digital multi meter and check the DC Offset and BIAS of the amp.

The caps most likely should be changed since it's an early to mid '70s amp (bad filter caps can cause hum issues) and you could be having some transistor issues causing the lower volume on the Left side.

Jehu02,
Thanks for the reply. Finally got around to some more checks on this Kenwood amp.

The following day I powered it up with the same connections from the first test. Strangely the hum is gone from the right side and if anything the left was louder.

The volume pot seems to be the issue on getting it balanced. I cleaned it again, and while in there I followed your suggestions, hitting the switch on the back. Gave it another test and everything seems to be balanced now.

As for the caps I think there might be some leaks, but being a noob I'm not sure. Following is a photo of two of the four 330uf 35v caps on the main power supply board. Photo taken from the top, if this is leakage I thought it would be exposed on the bottom of the cap instead of from the top. From what I can see the bottom side of these caps are clean.

And from the same power supply board the lone 100uf 16v cap, same brown residue on the top side but not the side towards the bottom of the amp.

Also this cap has me puzzled. The service manual parts list and PC board layout shows this cap to be a 100uf 10v, but the actual one on the board is a 100uf 16v

The following two photos show the 100uf 63v cap on the right and left main amp boards, but these were taken from the bottom of the amp, but again, I'm not sure these are leaks or did some of the caps get glued to the board?



I think I'm going to attempt the Main Power Supply board myself, and the large 15,000uF 63v caps. It looks like I will have to remove all the connections to the Main Power Supply board and remove the board to do it, just a matter of marking/documenting which wires come of which leads.

I just opened a fortune cookie that said: "No job is so simple that it can't be totally screwed up" and another "The road to success is always under construction"

Thanks for the advice.

The brown stuff that you see around base of those caps is glue. Not uncommon and often mistaken for leakage.

Regarding the discrepancy between schematic/parts list component values vs. what is actually installed: (again, not uncommon) go with what is actually installed as long as you believe it to be original i.e. done by the manufacturer and not by a hacker. In this particular instance, going up one step in the voltage of a cap does no harm. The voltage of a cap is simply a rating for the max working voltage it can handle. In this same vein, always note (and record before removing) polarity of capacitors as installed. Occasionally the markings on the PCB can be incorrect.

As for recap/refurbish projects I believe that access to the components is often the greatest challenge. And access varies considerably from one amp to the next.

My first major project was a KA-4006, two steps below your amp in the same family. Access in the KA-4006 is a bear. There is no bottom cover to provide access to the solder side of the main and power supply boards. And its tone board is buried deeply requiring significant dis-assembly to access, even then it is very tough. I don't know about the KA-8006 in this regard. Something to think about maybe.

Good luck...

BTW my KA-4006 was improved greatly by my work and it sounds wonderful. Right now I am finishing a KA-7100 that outclasses the KA-4006 and is very much easier to work on.

Dont remove those wires, you need to loosen all the front boards from the front of the chassis and remove the side screws all but two that hold the front on, the front will tilt. Look and you will see, the front pulls forward and tilts down. Once this is done you will have access to the ps board foil side.

Do NOT unwrap wire-wrapped wires. Big mistake. Whatever needs to be done can be done leaving the wires in place.

EchoWars said:

Do NOT unwrap wire-wrapped wires. Big mistake. Whatever needs to be done can be done leaving the wires in place.

Click to expand...

Just curious as to why? I've seen threads where it's recommended to add some solder to them to ensure a good connection after many years. If that's good advice, what is the difference between wire wrap and soldered connection that you wouldn't want to change it? IOW, why were some connections wrapped and others soldered? Inquiring minds want to know.

roger2, bktheking, jheu02,
Thanks all for the advice. Being able to do the caps on the power supply board without removing all the wires has saved me a lot of angst.

I've priced out the electrolytics for the power supply board with Panasonics from both Mouser and Digikey about the same price.

The 2 I'm having trouble finding are the 15000uf 63v that sit next to the transformer in the center of the chasis. The 2 connection 'lugs' on the bottom are larger than anything I've found online. I should have taken a picture while I had the bottom off - maybe it doesn't matter?

The KA-8006 gives access from top and bottom, but yes I believe the tone and filter boards are buried.

Regardless, I thought I would start with the Power Supply board, should I expect to hear any improvement, or does that come only after doing main amp, filter, and tone boards?

I have yet to see how the pre-amp performs on it's own. I've got a Pioneer SX-1000TW that sounds great, so I think I will take the KA-8006 pre-out to an Aux in on the SX-1000TW and see how it compares. That should give me an idea if I need to do anything with the pre-amp board on the Kenwood, yes?

BTW - it looks pretty :

You likely won't find large can caps with the 22.5 mm lead spacing (or whatever it was on those old caps). Standard is now usually 10 mm. I have found that the leads can be carefully bent with needle nose pliers and made to reach (barely). Other options...depending on the size of the solder pad, carefully drill new holes to accommodate the lead spacing. Option 2: 14/2 Romex as extender wires which are soldered to the bent snap terminals as pictured below.

John,

Nice Work! And thanks for all the advice.

I hope you all don't mind if I ask some more questions once I get some caps and get started on this, I'm sure some things are going to come up.

Jim

JamVal said:

....

I've priced out the electrolytics for the power supply board with Panasonics from both Mouser and Digikey about the same price.

Click to expand...

Both are excellent and are the first places most here go to for parts. I suggest trying them both. If funding is very tight DK has a free shipping option if an order is prepaid by check or MO. I believe Mouser has a better selection of transistors. If Mouser doesn't have a certain transistor then B&D might be next up in your search.

The 2 I'm having trouble finding are the 15000uf 63v that sit next to the transformer in the center of the chasis. The 2 connection 'lugs' on the bottom are larger than anything I've found online. I should have taken a picture while I had the bottom off - maybe it doesn't matter?

Click to expand...

This is another of the common hurdles in recapping. I suggest taking one of them out, measuring, posting pics here, searching various sellers, etc. I am going to respectfully disagree with the previous post. I could be wrong but I believe that 10mm is standard lead spacing for snap-in type caps, but there are other types out there. You may find a closer match or something easier to work with, with a wider spacing, in a different type of cap.

Sometimes a bit of improvising is required, sometimes not. My KA-4006 filter caps were replaced with computer type screw lug caps. Very neat and easy (also shown in my thread linked below). Also, you might search (AK advanced search and/or google search of AK) for threads on the KA-8006. I believe that pete_mac did one of these. I don't know whether he addressed this topic in his thread. But someone else may have.

Regardless, I thought I would start with the Power Supply board, should I expect to hear any improvement, or does that come only after doing main amp, filter, and tone boards?

Click to expand...

IMO you should be able to notice improvement by doing only the power supply board. In fact, it is a very good idea to do the work in small chunks and then test for problems before proceeding further.

I have yet to see how the pre-amp performs on it's own. I've got a Pioneer SX-1000TW that sounds great, so I think I will take the KA-8006 pre-out to an Aux in on the SX-1000TW and see how it compares. That should give me an idea if I need to do anything with the pre-amp board on the Kenwood, yes?

Click to expand...

Two things here:

1) Does KA-8006 have pre-out and amp-in connections? I ask because my KA-4006 does not, but it has something similar looking that is actually made for interfacing with a 4-channel set-up that existed back then. The link below is to the post in my thread about the 4-channel interface and its functionality.
http://www.audiokarma.org/forums/showpost.php?p=6217533&postcount=109

2) If your amp has real pre/main jacks then by all means test out each section separately before doing any work. As a general suggestion, observing everything you can before making changes is a good idea. Sometimes I have made a change and afterwards became aware of something that I had not noticed previously...then I am not sure whether the thing I am noticing was there before or whether I caused it.

BTW - it looks pretty

Click to expand...

Yes, it does

OK, one last thing specific to the KA-4006 and I would assume also your amp. The wires wrapped around the posts are solid, small, and fragile. Repeated bending can cause these wires to break, usually near the base of the post where the wire emerges from its winding. Efficiency in limiting the number of times any board with these wires connected needs to be turned over and back, as well as a gentle hand, is time and effort saved.

I used large BHC caps on both of the 8006's that I've restored. They are pricey but do be job nicely. Excuse the soldering on the filter caps in the pics - it looks much neater in real life!

http://www.audiokarma.org/forums/showthread.php?t=360313

The amp in the above thread remains the 'daily driver' in a good friend's main rig, and he has a wide variety of amps at his disposal - it sounds THAT good

pete_mac said:

I used large BHC caps on both of the 8006's that I've restored. They are pricey but do be job nicely. Excuse the soldering on the filter caps in the pics - it looks much neater in real life!

http://www.audiokarma.org/forums/showthread.php?t=360313

The amp in the above thread remains the 'daily driver' in a good friend's main rig, and he has a wide variety of amps at his disposal - it sounds THAT good

Click to expand...

pete_mac,
Thanks, great thread and beautiful work you did on that 8006.
three questions:
1. Where did you get the BHC caps?
2. I'm not a tech. I assume the BHC are the same value as the originals - 15000uf 63v, so why were they bypassed with the 2.2uf 250v caps?

and 3. unrelated to the large caps, the service manual shows a 10uf 50v cap on the power supply board that I can't quite see without taking everything apart, but it looks like an axial rather than a radial mount - is that correct?

roger2 said:

1) Does KA-8006 have pre-out and amp-in connections? I ask because my KA-4006 does not, but it has something similar looking that is actually made for interfacing with a 4-channel set-up that existed back then. The link below is to the post in my thread about the 4-channel interface and its functionality.
http://www.audiokarma.org/forums/showpost.php?p=6217533&postcount=109

Click to expand...

I think you are right. I have yet to find an owners manual, only the service manual. I just took a look at the schematics for the 8006 and those plugs are labeled "4 Channel". Thanks for the heads up.

roger2 said:

This is another of the common hurdles in recapping. I suggest taking one of them out, measuring, posting pics here, searching various sellers, etc. I am going to respectfully disagree with the previous post. I could be wrong but I believe that 10mm is standard lead spacing for snap-in type caps, but there are other types out there. You may find a closer match or something easier to work with, with a wider spacing, in a different type of cap.

Sometimes a bit of improvising is required, sometimes not. My KA-4006 filter caps were replaced with computer type screw lug caps. Very neat and easy (also shown in my thread linked below). Also, you might search (AK advanced search and/or google search of AK) for threads on the KA-8006. I believe that pete_mac did one of these. I don't know whether he addressed this topic in his thread. But someone else may have.

IMO you should be able to notice improvement by doing only the power supply board. In fact, it is a very good idea to do the work in small chunks and then test for problems

Click to expand...

Yes, there can be non snap-in caps with other lead spacing than 10mm. Personally, I stick with low ESR, High Temp caps like TS-HA from Panasonic or the KMH series from United Chemicon. There's also the Cornell 381LX series that I believe are 105 C, low ESR. I won't pay a premium price or go to a low temp "standard" cap just to get lead spacing right when extending the leads works well for me.

There's certainly the option of using screw terminals, but that will probably require other, but different mods/wiring unless the original design used screw terminals. To each his own. You can probably measure lead spacing without even removing the cap unless it's buried under some other board so that you can't see the trace side.

Doing chunks and testing is great advice, though I rarely follow it myself. I'd rather get in and do all the work I'm planning, but perhaps the next recap i do I'll make it an experiment...PS, test, one channel, test and compare sound. Then the other to match.

Edit. The link finally worked for Pete_macs rebuild so I can now see that the caps aren't soldered into a board, but just clamped in place. Your main issue here now isn't the lead spacing or style, just the diameter of the original cap and finding a like size replacement, or at least one close enough that a little ring of PVC could go over the cap to allow the clamp to tighten. The use of screw types here makes perfect sense as simple ring terminals can be soldered to the wires and then attached to the caps.

However...looking at the price of screw terminal caps, I'd probably solder ring terminals to the snap-in leads and then solder the wire connections to the correct ring of the terminal. Again, to pay double the price when it really doesn't gain me anything seems silly to me.

John,
Everything you've advised makes perfect sense to me. Thanks so much.
I think I can do this, at least the power supply and large filter caps for starters, although it's been a long time since I've done any soldering, so I will practice first on something of no value.

I found another webpage that shows an 8006 recap. http://iamthejeff.com/post/21/kenwood-ka-8006-amplifier

He used smaller diameter caps and wrapped them in foam to fit the clamp.

Thanks again.
Jim

That is an interesting external thread. I haven't read it read it yet. But glancing through it looks like he did a good job and provided some nice pics and other info. <EDIT: I have read that thread now. It looks like a super nice job and I like his idea of replacing the relay and also the hot-running resistors on the PS board>

I don't know if I would feel comfortable with foam sleeves as a mounting method for the big caps though. Over time, wouldn't the foam compress slightly loosening the mechanical connection? I don't know, just thinking out loud here I guess. If the mechanical connection did loosen up a bit, it might put some mechanical stress on the wire connections, which would not be ideal. There could possibly also be some small movement due to expansion/contraction with thermal cycling.

If I had to use a smaller diameter cap I would try to find some other way. I have seen use of a cut-off portion of PVC pipe as a sleeve. I think it may have also been split down the side. That may have been one of the projects at cdkands site, not sure though.

I'm sure there are yet other ways to improvise a solid mounting system.

Or, following pete_mac's lead would, IMO, be the best possible choice since the diameter matches the original and those caps are probably better quality than anything else that you are gonna find.

Another option if all else fails with finding a close diameter match is to restuff the original cap can like is done with the multi-cap cans in a lot of tube gear. Here's a couple pics of a multi cap I stuffed. It was from the tuner/preamp section of a console and there wasn't enough room underneath to mount the replacements individually. Yours would be much simpler as there's only one cap that would need to be stuffed. It's especially useful if you want to keep the vintage feel and like the look of the massive caps, but again, for me, I'd just go with new caps and get spacers if needed to make the clamp fit properly.

I forgot to add, if you haven't already placed your purchase, I'd highly recommend getting 2 new 1K multi-turn trimmers for when you need to set your bias. I'm fine with Murata, some swear by Bourns. Here's the Murata offering with "Y" leads and side mounted adjustment. The multi-turn trimmers are much easier to fine tune than the old, single turn ones which could have some corrosion dead spots since they weren't sealed. These will go in the Vre1 spots on each amp board.

http://www.mouser.com/ProductDetail...GAEpiMZZMvygUB3GLcD7u3z%2bNHL9M9L/IIw1LsaOGI=

jheu02 said:

Another option if all else fails with finding a close diameter match is to restuff the original cap can like is done with the multi-cap cans in a lot of tube gear. Here's a couple pics of a multi cap I stuffed. It was from the tuner/preamp section of a console and there wasn't enough room underneath to mount the replacements individually. Yours would be much simpler as there's only one cap that would need to be stuffed. It's especially useful if you want to keep the vintage feel and like the look of the massive caps, but again, for me, I'd just go with new caps and get spacers if needed to make the clamp fit properly.

Click to expand...

Neat stuffing job! How do you re-attach the can top to the base?

I also liked those pictures of the filter caps with the new wire extensions, that's a handy trick.