• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Kenwood KA 6000 output transistors?

gonzothegreat

gonzothegreat

Super Member
I just dug this one out of storage after hearing Echowars rave about the KA7000. I looked at it ten years ago when I first found it in the trash but I never put much effort into it.

I know it has some serious DC on the outputs (I forgot how much but it was more than a few volts) but I'll worry about that later.

I think the outputs may be bad and the previous owner subbed NTE transistors (NTE280 I think). What are the original japanese TO-3 transistors?

ObBrag: Just picked up a Sansui 8080 and a Pioneer sx-780. Haven't even had time to test them.

Virtu-Al
 
Register to hide this ad
ooooo...nice score on the 8080 and SX-780! Very nice pieces, both of them, and well worth putting time into.

:)

TP
 
Check the model again. There is a Model 600 integrated, and a KA-6000. There was no KA-7000, but there was a 700M amplifier, KA-7002 integrated, KA-7300, and a KA-7100.

The KA-6000 is a real oldie if that's what you have. From 1970, and rated at 58WPC. Pretty early in the Japanese solid-state design phase, and I'd have no idea what it might sound like. Tuned and tweaked it ought to sound fine.

If you need output devices, just get a couple of pairs of the all-purpose 2SD424 / 2SB554 devices and fuggetaboutit.
 
You were right EW - I was refering to your 700M that needed the new diff pair to correct the DC offset.

As for the outputs, it has NTE280 TO-3 all around and not the complimentary outputs of "modern" receivers. It reminds me of my old Scott R357 I used to use with my Lafayette electrostatic headphones 20 years ago.

This is an interesting amp. Some Italian site said it was from 1968 (as old as I am :) ). Unfortunately the case bottom and cover are missing. I'm thinking of slapping on some thick acrylic plastic since the inside looks cool (though cramped) for a see-through case. I don't see many amps with the old Dynaco mid-size case.

Virtu-Al
 
What are the original japanese TO-3 transistors?

Virtu-Al [/B]
Click to expand...
I have a KA-6000 that I repaired about a year ago. The original output transistors were 2SC898. I looked into replacement transistors and decided not to go with the NTE or original replacements because of the cost. I ended up using some 2N5878's. At the local surplus store they cost $0.85 ea. I bought ten and was able to get two reasonably well matched pairs to use as replacements.

Since repairing the amplifier about a year ago it has proved to be very reliable. The KA-6000 was reviewed in the December 1968 issue of Stereo Review. You may be able to find a back issue copy at your local library.

edit: Since writing my original reply I obtained a manual. The service manual indicates that the RCA 2N3442 is a suitable output transistor replacement. These are available from Mouser at a reasonable price.

One drawback to this amplifier is that it is noisy. This is due to the unusually high gain (46bB) in the amplifier section. I am working on a modification to reduce the noise by reducing the gain. I expect the results in a couple of days.

According to the instruction manual that came with the amplifier, the output power with both channels driven is:

41 / 41 watts at 4 ohms
45 / 45 watts at 8 ohms
34 / 34 watts at 16 ohms

Sincerely yours,

tcdriver
 
Kenwood KA-6000 Noise reduction.

The following is an update to my earlier post:

I had observed that there was more noise from my Kenwood KA-6000 output than I would expect from a high quality amplifier. With medium to low sensitivity speakers, such as my Advent loudspeakers, the noise was just audible from my normal listening position. However, when I connected the amplifier to my pair of high sensitivity Altec A-7 loudspeakers the noise was apparent to the point that I deemed the combination unsuitable.

Looking into the source of the noise, I discovered that the amplifier section of the KA-6000 was designed with an unusually high gain of about 46.5 dB. With gain this high, one will hear a hiss through the speakers even if the volume control is set to minimum. I found that by replacing the 470 ohm resistors R911, R912, on the Main Amp board, with 1.82k ohm resistors that the gain could be reduced to a comfortable 35 dB. This 12 dB reduction in gain brings with it a 12 dB reduction in noise. The high level sensitivity is now about 600mV for full output into an eight ohm load. Most sources will have enough output to drive the amplifier to its full output.

I would recommend this modification to any owner who wants to lower the noise of their KA-6000.

Sincerely yours,

tcdriver
 
If you need output devices, just get a couple of pairs of the all-purpose 2SD424 / 2SB554 devices and fuggetaboutit.
Click to expand...

Now that's what I'm talking about! Where do you get those?
 
I've got one I picked up at an antique store about '92. He only worked on tubes so didn't try it. All that was wrong was a blown fuse. It's been a reliable back-up amp and served as the main amp quite awhile while my Mitsubishi was out with bias issues.

It sounds nice, not superb but does the job if not pushed too hard. I can testify to the power loss at 4 ohms. Wimpy supply begins to sag and distortion goes up. When you switch in both speaker pairs, they are connected in series for 16 ohms. The pre-amp has a weak output, matched to that over-sensitive amp section so it's not too useful subbing in to drive other amps.

-Ed
 
I have the KA-6100 amp, it's rated at 50 watts RMS at 8 ohms impedence, I think it might be 60 watts at 4 ohms, from 20 to 20,000 cycles with, I think, .03 distortion. In any case it sounds just great. Since it is old, I do have to keep the controls active or some noise will come into them. For example the volume control, I move it around every few days just to keep the pot clean. I'm driving the Insignia $49.99 specials with it and it's perfect in my living room with them. It compares very favorably with the AR amplifier I once had. Oppppps! Sorry I now see this is an old thread. I'll leave the info anyhow, just in case anyone else is interested in the KA-6100.
 
This is an update on the noise issue described in post #6. After modifying another KA-6000 to reduce the gain, I noticed that it still had a little more noise than I would have expected. Looking at the schematic, I realized that the two transistor amplifier stage driving the power amplifier section was made using 2SC458 transistors. The 2SC458 transistors of that era have a well deserved reputation for becoming noisy. Based on a recommendation that Fred Longworth made in one of his posts, I purchased some 2SC2240 transistors to replace the 2SC458s. The 2SC2240 replacement transistors made another significant reduction in noise in my Kenwood KA-6000. I recommend this transistor substitution.
replace2sc458.jpg

keyword kenwood6000
 
Last edited:
Thanks for that. After 4 1/2 years of sitting on the edge of my seat, my ass was getting a nasty crease in it.

Glad you have it sorted out.
 
Sounds kinda simplistic but was working on an old Fisher receiver that was motorboating, checked everything finally I pulled out the plug in boards cleaned all the contacts then reinstalled them and no more motorboating. Did the same to my Kenwood KA-6000 and so far, playing for about 10 hours no noise just sweet music. Going to do that resistor swap to lower the gain. Thanks tcdriver
 
You must log in or register to reply here.
Back
Top Bottom