Developing the BOM for a Kenwood KR-6160 restoration

tonefoto said:
I know this is an ancient post but I'm going to add to the mystery noise on the KR-6160 after recap. I've recapped a couple of these receivers so far. I'm not a big fan of Kenwood I have to be honest. This one really sounds exceptional so I think it worthwhile to resurrect them. I too had recapped the amp, toneboard and preamp boards but still had this white noise at no volume, audible when your ear is right up to the speakers. Surprise to me, I found that giving the MIC pot a good cleaning with Deoxit cured the noise for me. YMMV.
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The MIC circuit also uses a 2sc458 which, by this time, is adding plenty of noise... sometimes quite loudly.

A "fast" way to cut the noise, if you don't plan to sing karaoke through this fine receiver, is to detach the MIC circuit from the rest of the unit.
 
I have a question. After replacing so many components, have you noticed a change in the sound? And more importantly, have you noticed an improvement? Because I think this amplifier sounds great, but it's a bit lacking in accurately reproducing the low and mid-low frequencies, where I'd like more clarity. Otherwise, I have nothing to complain about. So I'm wondering if this flaw is inherent in the design or if it's simply the components aging.
 
dlucy said:
The MIC circuit also uses a 2sc458 which, by this time, is adding plenty of noise... sometimes quite loudly.

A "fast" way to cut the noise, if you don't plan to sing karaoke through this fine receiver, is to detach the MIC circuit from the rest of the unit.
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I have a question. After replacing so many components, have you noticed a change in the sound? And more importantly, have you noticed an improvement? Because I think this amplifier sounds great, but it's a bit lacking in accurately reproducing the low and mid-low frequencies, where I'd like more clarity. Otherwise, I have nothing to complain about. So I'm wondering if this flaw is inherent in the design or if it's simply the components aging.
 
We're talking about this particular amplifier, which I find similar but superior to many of the much-vaunted Sansuis. But in general, I think this is also a question that should be asked about many older devices: how much or when it's worth replacing various components.
 
Pfrullo said:
We're talking about this particular amplifier, which I find similar but superior to many of the much-vaunted Sansuis. But in general, I think this is also a question that should be asked about many older devices: how much or when it's worth replacing various components.
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That is a question for a different thread. It has been asked many times, answered hundreds of times. Lots of different answers. Use the Search function and you'll find plenty of responses... or start a new thread on that topic, if you prefer.
 
Pfrullo said:
I have a question. After replacing so many components, have you noticed a change in the sound? And more importantly, have you noticed an improvement? Because I think this amplifier sounds great, but it's a bit lacking in accurately reproducing the low and mid-low frequencies, where I'd like more clarity. Otherwise, I have nothing to complain about. So I'm wondering if this flaw is inherent in the design or if it's simply the components aging.
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For my ear, the differences (improvements) were obvious and strong. But that's just my hearing and my opinion.
 
ducati2 said:
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Qe5,Qe6 are listed as 2SC627 in the schematic, but I can't read the label on these. The datasheet for 2SC627 is typical and boring until you reach the hFE of "360 minimum".​
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2SC627 NPN CBO=200 CEO=200 IC=100mA Pd=700mW fT=20MHz hFE=360​
​
So, these will have to be high output and it took a thorough run through alltransistors to find devices that matched and Mouser to find one that was available and matched or exceeded. I'm going to try ZTX696B instead of a Darlington since I really don'[t know enough about them to select and replace them confidently.​
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Ok so after receiving my ztx696b replacements for Q5-6, I see they are nothing alike. Oem was metal with a metal radiator affixed, will this not matter?​
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Hi everyone. I know this is an old thread but in my searching for answer to my question the above post sums it up perfectly. However, I don't believe ducati2's question was ever answered.

My unit is the Kenwood KA-6000 and the 2SC627's are on the main amp board with little heatsinks around the TO-29 package.

So my question is, can the ZTX696B be installed without a heatsink? I see that these E-Line devices are rated at a higher temperature. But my understanding of electronic circuitry is limited and I'm not sure how to calculate the power disipation as it relates to temperature so I'm asking if anyone has the easy answer.

Another possible replacement is the 2N3440 in a TO-29 package that I can re-use the existing heatsink thingy. But looks like the Hfe of the 2N3440 is 160(?) where as the 2SC267 is min 360. Is this going to matter? Some random dude on a facebook post wrote "HFE is generally unimportant in the application here. Iirc one is for the VAS stage which should have compensation, and the other is for the bias circuit which is VBE dependent". This was for Pioneer SX1000. I don't know what that all means and if it applies to my KA-6000 circuit.

Any advice and help is always appreciated. If anyone thinks I should just start a new thread, please let me know.

Thanks.
Marc
 
MarcD said:
Hi everyone. I know this is an old thread but in my searching for answer to my question the above post sums it up perfectly. However, I don't believe ducati2's question was ever answered.
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If I had one and wanted to do all this work, I'd use jeffery's transistors in post 55. And add heatsinks.
 
MarcD said:
Thanks. Those are obsolete, heavy sigh. That's the problem with old threads. Probably going to go with the 2N3440.
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Sorry about I have them in my stock. I didn't think to check availability
 
dlucy said:
Preamp board first

It's on the topside of the chassis, mounted by itself, and you just have to carefully document the wires, cut them, pull out the board, replace the componets, then put it back in. No problem.

View attachment 1123426

View attachment 1123428

View attachment 1123429

I don't have time to replace all the components, so the trimpots, non-electrolytic caps, and resistors get to stay... even as ugly as they are an as coated in old rosin or whatever....

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Here's a better view of the silkscreening once the transistors and electrolytics have been removed. Easier to see the component numbers and the transistor pinout diagrams this way. Triple-checked the outgoing transistors with the Peak Atlas DCA75 Pro and the silkscreen on this board are correct.

View attachment 1123432

The schematic tells us what should be in there:

View attachment 1123434

A quick sketch from before removing the components reminds me where the polarity for the electrolytic caps are, what my transistor check revealed, and what values came off the board:

View attachment 1123435

The two 2SC871 and two 2SC458 all get replaced with KSC1845FA.

The electrolytics all get replaced with higher-voltage Nichicon KL series low leakage caps (except the one value I didn't have).

View attachment 1123437

The trimpot gets a good Deoxit-ing and FaderLube-ing and it all goes back in place. I'll have to locate the service manual procedure for setting the one trimpot. Hmmm....

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To do list:

List all the caps that went in.
List the caps that should have also been replaced
Point to the trimpot adjustment procedure.
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Hey there Dlucy, this is some solid work you've documented here good on ya! I am repairing a 6160 for a friend and there's some sentimental value here (it was his dads and has some fond memories of it being around when he was growing up). Hoping to bring it back into use for the next generation.

I was writing to ask if you ever figured out what the trim pot is for and how the adjustment procedure goes Vrd1 on the schematic. no info in service manual for it.. hmm. any wisdom welcomed!

PS, is pretty close quarters working inside this thing, not surprised you pulled the boards fully I'm considering the same.

Cheers
 
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