| audio, gear, kenwood, vintage | 24 comments

I did a decent amount of repair work to this Kenwood receiver, compared to my usual restoration routine. And I remembered to actually take photos of the whole process this time. Lots of photos!

I'm starting to run out of ways to introduce all of these receivers that I've been finding lately. I've been extremely lucky to come across so many this winter—it's usually the in spring and summertime that this happens, mosty likely because people are cleaning out their garages.

This Kenwood KR-6400 is rated at 45 watts/channel and has pretty much all of the standard features you can ask for on a vintage receiver. From what I could find, it seems to be related to the KR-5400 and the KR-7400. All three share a similar faceplate design with the tuning and volume knobs protruding through the tuner dial glass. It looks like you can pass a quadraphonic signal into the back, but I'm unfamiliar with how it works. Normally this feature is a huge selling point, so I found it strange that it wasn't mentioned anywhere on the faceplate. The owners manual seems to confirm that you can in fact listen to 4-channel sound with this receiver, but it probably converts it down to stereo or something.

As usual, most of the lights were burned out when I got it home, so once again, I ordered replacements from djwogo.com. The original style of bulbs were unfortunately no longer in production, so I had to make due with a slightly different crimp style

The replacements fit pretty good in the original rubber holders, but I had to stick the bottom end in a little further to angle them up so that the bulbs weren't resting against the internal plastic enclosure.

With the new bulbs installed, it was looking fairly pretty, but there was still another small problem. Whenever I powered the receiver on, no sound could be heard at all until I cranked up the volume. Once I did that, the sound would kick in and I could reduce the volume back to a normal level. I've had this problem before with my Sansui AU-5900, and the culprit was the protection relay. The tiny little contacts get dirty with oxidation over the years and cause trouble. With the Sansui, I was able to simply remove the plastic cover from the relay and gently rub the contacts with a piece of paper soaked in contact cleaner. It did the job, but I found out that they still sell the exact same relay used in this receiver today, and it was only $13 on Digikey. So I figured I might as well do the job right and replace the part entirely. For anyone wondering, the manufacturer is Omron and the part number is MY4-02-DC24. 

To remove the relay, you just need to remove a couple screws on the amp board and lift it out, then tilt it back to access the solder joints.

The new relay was almost identical to the old.

I've gotten a lot of soldering practice lately so the installation was fairly easy. It helps if you bend a few of the pins back to hold the relay in place while you solder it in.

With the relay replaced, it was working perfectly again! One useful tip to test whether a relay is giving you trouble or not, is to gently tap on the plastic case while the receiver is running. If you hear static through the speakers, you should probably replace it. Or at the very least, try to clean the contacts.

And of course, as usual, I made one final adjustment to the bias current, setting both channels to 50mV by adjusting VR1 and VR2 on the amp board. Perfect!


Hey! I also have a Kr-6400. I came across your post as I am curious as to what type of quadrophonic equipment I would be able to hook up to it. Where would I be able to find a Quadrophonic adaptor and are there radio stations that even broadcast in quad or is it for quad vinyl, reel to reel and or quad 8 track?

Hi Charlie. Unfortunately I am not sure what kind of quad adapter you would need, or where to get one. I also don't know what kinds of components would be compatible, since there were several different quad formats back in the day. You'd probably have better luck asking over on http://audiokarma.org

Just curious, but how do you keep your amps and PCBs looking like new? I've got some similar gear and no matter what I do they don't look that great...

For the faceplate and knobs, I just use warm soapy water with a microfiber cloth. For tough grime I use a melamine foam sponge (Magic Eraser). Obviously careful not to wipe away any lettering.

For the interior and PCB I use a can of compressed air to get rid of most of the large dust particles. Then I use a 1 inch soft bristle paint brush dipped in 99% isopropyl alcohol, and I gently brush the boards to pick up as much remaining dust and grime as I can. I blow it dry again using the compressed air—the alcohol evaporates quickly.

How is the sound in this reciever?

I hate describing the sound of any audio equipment, so I'll just say that it sounds "good" :)

Nice job on the re-furb. I just picked one of these up a month ago, in mint shape plays fantastic...enjoy your blog.

Hey looks great! What voltage of bulb did you replace the burnt out ones with?

Jason, I believe they were 8V 250mA

Hey there: I just bought one of these KR 6400's on ebay. I had a kenwood (model unknown) when growing up after moving to live with foster parents in 1968. I decided to try and find the exact one from that time in good shape for sentimental value. I couldnt find which model it was so ended up with this one yesterday on ebay. And just now saw an old ad on ebay from 1968 advertising this receiver. However the manual has no dates on it.Can anyone confirm this is the year it was made? Thanks!

Sweet. Two phono inputs and three speaker connects. Reminds me of my old Onkyo TX-4500, which in addition boasted Tape 1, 2 and 3, which let me dupe my reel-to-reel tapes to two cassettes simultaneously.
Ten years later my wife bought me one of the early Revox single CD players which I ran on the Tape 1 input. I made cassette copies to play in the car.
Myrtle Beach SC

Hello Jeff i would like to ask if the relay would be the same for the Kenwood Kr-5400 and if so is there anyway you can tell me where did you purchase the new relay from or what part number did you use ? Please any information would be appreciated as I have changed the caps and still the relay would not engage but before I changed the caps and tapped on the relay with the original caps (old ones ) still installed the relay would engage and the receiver would play fine until I shut it off and when I turn it back on I would have to tap the relay again for it to work . I resoldered all of the joints no luck . I replaced the big caps and not tapping will not do anything . Could this be the relay itself ? It is a kenwood kr-5400 model

Rennie, you'd have to look at the service manual or perhaps even remove the original relay to determine what a modern replace ment would be. I ordered mine from digikey and it was around $12. It's possible the relay is at fault, as the contacts inside can get quite oxidized over time and they are hard to clean.

Nice work man! Just picked one up on eBay last week..it's missing the wood. Any idea where to find replacement? or, measurements? (Merry Christmas!)

I bought my Kenwood 6400 new in 1976. It is the only amp I have ever owned and it still sounds great.

My co-worker asked me to clean out the interior of his kr6400 and the speaker select knob has a lot of built up grime and dust on it. I recently bought some Deoxit for cleaning my guitar's pots but I'm hesitant to use such a powerful chemical on vintage gear. So for now I'm gonna try to clean it to the best of my ability using only alcohol and compressed air instead. Thoughts on using Deoxit?

PS this amp was out in his shed for years so it's pretty dirty and has been exposed to the elements. Still works though!

On the contrary, detoxit is the standard go-to cleaner for vintage audio gear. You'll see it recommended everywhere for stereos and I've used it myself with great success. Go nuts!

Hello. do you have any idea on voltage and current for the stereo indicator lamp?

Hola yo tengo un kenwood KR6400
quiciera saver cuantas bosinas le puedo poner o de cuantos whats

Hola yo tengo un kenwood KR6400
quiciera saver cuantas bosinas le puedo poner o de cuantos whats

How much are they worth, the kr-6400

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i have one from 1970. i have a 4yr old Colby tv. can i run my sound system thru the AUX channel?

Hi Jeff, I just lucked into one of these and am trying to reove the faceplate for a good cleaning.
Can't seem to pull off the balance knob. I can see no set screw. any ideas?