Kenwood KA-6000 as a pre-amp?

SigloOne

Active Member
I was recently gifted a Kenwood KA-6000 integrated amplifier and a Kenwood KT-7000 tuner. They haven't been used in a while (over 5 years) but were in good shape before that.

I want to use the KA-6000 as a preamp for a tube amp I am building. My concerns are what to do about having no speaker load on the unit, I know in tube amps this is disastrous and will toast transformers. Can the amplifier section be disabled?

Also, should I be concerned about the existing capacitors in the unit? I know with vintage tube gear they generally need to be replaced. But solid state is not my forte.

Any help would be appreciated.

-Steve
 
i'm really no authority

does the unit have pre-outs on the back? that's a pretty good indication of it being appropriate for use as a preamp. if the speaker switching has a "speakers off" setting i would use that. if there is no such setting, perhaps a pair of 8 ohm resistors across the speaker terminals would be appropriate. you could also run some dedicated low frequency drivers off the speaker taps of the KA 6000. plus here's an earlier post on your unit http://www.audiokarma.org/forums/showthread.php?t=223751
 
Yes it does have pre-outs on the back. I will have to take a good look at the controls to see if it has a speaker off position. I didn't notice any but wasn't really looking either. I didn't think they would have that.

Thanks for the input.
 
if you pull the jumpers you can still patch through to the power amp section of the kenwood with some y-plugs. i would suggest using it drive some low frequency drivers to give the low end of your tube rig some bottom end. what kind of a tube amp are you going to be running and with what sort of speakers?
 
The tube amp I am building is a push-pull design using 12AT7's on the front end and 6CW5's for the power tubes. I will be running the amp into a pair of Cerwin Vega speakers that have a 92db/w efficiency. Should be pretty kicking. Eventually I would like to get a tube preamp like a Dynaco PAS-3 or a Fisher, but haven't found one in my price range yet. I am cheap and poor, lol.
 
Can the amplifier section be disabled?
Yes, by removing the jumper wire between the pre-amplifier output and the main amplifier input you will not have to worry about the power amplifier section. There is need to add load resistors to the unused amplifier outputs.

Also, should I be concerned about the existing capacitors in the unit? I know with vintage tube gear they generally need to be replaced. But solid state is not my forte.
Some capacitors age better than others. In general paper and electrolytic capacitors will be effected by age while polyester, polystyrene and polypropylene will not be effected much by age. The Kenwood KA-6000 and KT-7000 were made in the late 60’s or early 70’s and unfortunately use a lot of electrolytic capacitors. I have found that some (very few) electrolytic capacitors have gone bad in my KA-6000 units. I would recommend checking the distortion and frequency response of your KA-6000. If they check out good, you may be able to put off replacing the electrolytic capacitors for a while.

The preamplifier section gain of the KA-6000 is negative. That is, if one feeds in a signal, tone controls flat or out, with the volume control set to maximum the signal will be about 5.5dB lower at the output.

Also keep in mind that the KA-6000 is stuffed full of 2SC458 transistors which are notorious for becoming noisy with age. If you find that there is more noise from the preamp section than is acceptable, replacing the 2SC458 transistors will fix that problem.

There is a lot of good information to be found here at AudioKarma by using the search engine with the keyword: Kenwood6000. Let us know how your project turns out.
 
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