Kenwood 600 Supreme restoration (and nudies!)

[Pacific Stereo]

I've had a 600 in the lab for the last week or so. The owner wanted a full restoration, so it's been thoroughly gone through.

These are absolutely beautiful integrateds, both cosmetically and electronically. Full dual-mono everything, class-A prestages, a nice (if oddly complicated) power supply, FET differentials and direct-coupled power stage with no caps in the signal or feedback paths. Very sweet and smooth-sounding, with excellent detail and speed.

There are a lot of things to do to these, and they are damn annoying to work on. Since the power supply is the one thing that is easy to work on, I started with that. Why the rest of the amp isn't made this way, I simply don't understand. But it isn't.



This supply got a full recap, replacement of regulators, error drivers and zeners, "carbon glue" cleanup and tweaking of gains to bring voltages to where they belong.



I always seem to forget to take "before" photos, and I did again this time, too. Suffice to say that the amp was dirty inside, with a lot of "sticky dust" that doesn't just blow out. The main filter caps on these always tend to be bad, but this one's were still all right. However, since the unit was apart and this was the opportunity, the customer and I agreed that it made sense to go ahead and change out the filters, since it's difficult.

And look at that BEAUTIFUL precision attenuator! Oh, the stuff of dreams.



I ended up using some snap-in parts because I don't really like what's available in the screw-terminal department. These are better parts with a ripple-current rating of 11 amps each. They're slightly smaller in diameter than the parts they replace, so I glue some foam to the new parts to make them fit in the clamps correctly. You can just see it between the clamps and the parts. Oh, and see the output relay on the board in the center left? Guess what you have to do to change it? Yup. Remove those capacitors. Oh. You want to remove the capacitors? Remove the transformers.



All the other boards were recapped and serviced as well. The power stage boards were serviced, drivers replaced (those funky-can 2SA810s and their counterparts are time bombs), new sealed Bourns bias and offset pots were installed, and a few other various and sundry items were addressed.

Then it was time for BeautyMaker. This customer wanted the outer case redone, so along with the usual, she got some new paint, too. I've developed a method that duplicates the factory "splatter paint" effect quite nicely, and that was done here. So a little paint and polish, and voila!







After a 12-hour burn-in, she is ready to go back. Hate to do it, though, I'd just like to keep her!



NOTE: The volume knob is quite gouged up on the front. It's not easy to see because of the lighting, but it's there. I'd like to find a replacement for this customer. So if y'all wouldn't mind keeping your eyes peeled, I'd appreciate it.

Photos are copyright 2012 by Pacific Stereo. Absolutely NO unauthorized use or copying is permitted, and specifically, NO EBAY USE is permitted.

[goodrat]

So how does it sound?

[Pacific Stereo]

Originally Posted by goodrat

So how does it sound?

Absolutely delightful. Would keep it if I could.

[ke4mcl]

thats soooo not fair!!!

this guy's got mountains as a backdrop! not fair at all i tell you!

[Nakdoc]

Good job! Did this one have double sided boards? When I encounter the early feedthru types I often have to add hardwire jumpers.

[VintageSteve]

As always, a superb looking restore! (Is that leaky capacitor gunk on the power board?)

[Pacific Stereo]

No double-sided boards in this one. The stuff on the power boards is the carbonized glue, though this one did have several leaking small capacitors in various places.

[DaveInVA]

Very nice! I like the flagship Kenwood stuff. I have a 7002 kicking around here somewhere along with its matching tuner.


Dave

[Socal Sam]

PS, nice work as usual on all your stuff. Very impressed with the wide range of gear you do. Keep it up!

[NAD613]

Nice work! There sure were some nice looking integrated amps back in the 1960s-70s.

[Pacific Stereo]

Well, just putting another one of these in burn-in. This one had mondo leaky main filter capacitors, as ugly as they come. It also had a problem I have seen only once before, and that's self-destruction of the detent mechanism for the precision attenuator. This causes the VC to lock up at various points in its rotation, very scary.

Alps put the detent mechanism in the MIDDLE of the attenuator instead of at the end, so service is well-nigh impossible. This control is so rare that one does NOT want to disassemble it under any circumstances.

It's now fixed, but it's a nerve-wracking feeling, because one can't just go out and get another one of these. The detent function is gone, but that's a small price to pay.

I'll have to see if I have any new photos of this one worth putting up. She sure sounds nice, though!

EDIT: Here are the caps.

One thing I just don't like about these is how hot they run the pass transistors in the power supply. Hard to see, but if you look you'll see added heat sinks on the four devices at the top. This is different than the earlier one in the thread.

[Pacific Stereo]

And the last track before she goes to the load resistors is...

Peter Murphy - Indigo Eyes.

[Trekmaster]

Very cool been awhile since I've seen any new restore pics. I notice you don't have any restore pics of a 950 hint hint

[HKken]

Beautiful! The Supreme series was awesome!

[Pacific Stereo]

Originally Posted by Trekmaster

Very cool been awhile since I've seen any new restore pics. I notice you don't have any restore pics of a 950 hint hint

<sigh> The world it turns, from sun to sun, and Pacific's work is never done...

[Pacific Stereo]

I had one of these come in for some additional work. This is the second Kenwood I have run across with switches and controls so dirty that my standard treatment just isn't enough. The trouble is that it is impossible to know this until trouble crops up again. After a year and a half, this owner wanted them gone through again. This time, I have modified the procedure and expect a good outcome.

One of the things I do not like about the 600 is how hot they run the power supply pass transistors. Even with the additional heat sinks, they are too hot to touch for longer than abut three seconds. That's just too hot in my book, even though I know what the specifications say. I took some additional measurements and made some calculations, and the devices are indeed safe, but that doesn't mean I have to like it. So what do we do when we don't like something? We change it!

Since we have some convenient metal right next to the supply, it makes a lot of sense to move the devices there.



They're connectorized, so that the board can just be popped out, just like before.



The paint under the devices was removed. And now they run cool as cucumbers. I like that. She's back in burn-in, and expect to have good news to report to her owner tomorrow, as the switches and controls are once again working very nicely.

Love the way this amplifier sounds. It's got something... something about it.

[HKken]

Nice work, PS!

[S10LAKE]

Great work PS!

I can't wait for you to go through my Pioneer SX-1980

Steve