Another Kenwood KA-7100 recap

leesonic

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I did another Kenwood recap last week, I didn't do that much different to the first one I did.

  • I replaced the four transistors in the tone control circuit as it all went quiet when the tone was switched on.
  • I also removed the output transistors, and put in new insulators that don't require heatsink grease.
  • The protection relay was taking it's sweet time to click on, so I replaced the troublesome Q34 transistor and D27 diode.
  • I added heatsinks to the two transistors in the power supply that run hot.
  • Finally, I polished the actuator rods that connect the front panel knobs to the switches inside for speakers, tape monitor, and source selection.

Since I like taking pictures, I thought I would post them here.

Lee.

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Nice work, nice pics :thmbsp:

In the 7100, is the board with the RCA connectors difficult? Anything underneath that is hard to get to? Or did you remove the RCA's?


Also, did you have to undo wirewraps anywhere to improve access or remove a board?
 
Good work.

Only criticism: Should have replaced those tantalum caps (C25, C26, first pic, 0.33µf 25V, use a stacked film cap here), and popped in a new protect relay.
 
Nice work, nice pics :thmbsp:

In the 7100, is the board with the RCA connectors difficult? Anything underneath that is hard to get to? Or did you remove the RCA's?

Also, did you have to undo wirewraps anywhere to improve access or remove a board?

Thanks.

Only thing hard to get at is a single cap under the RCA connectors. Desoldering it is easy. To replace it, cut the leads down on your replacement cap, and carefully insert it using a long pair of tweezers or needle nose pliers. It should only take a couple of attempts, make sure your holes are clear of solder.

As for the wirewraps, or anything else to remove, I cut all the wires to the 5-pin DIN connector at the back to remove the rear board. I didn't bother to put them back this time, who uses DIN connectors any more? There's a single ground wire soldered onto a screw high up on the back panel that needs to be cut to work on the board, and re-soldered when you put everything back together.

EchoWars said:
Good work.

Only criticism: Should have replaced those tantalum caps (C25, C26, first pic, 0.33µf 25V, use a stacked film cap here), and popped in a new protect relay.

Thanks also.

No need, those caps are for the subsonic filter. I've never ever found myself using one in all the years I've been listening to vinyl. Old relay was working fine.

Lee.
 
Very nice work. How does it sound compared to before? I want to do my 8100 but I'm wondering if I should since it sounds pretty good as is. Suggestions?
 
captaingamez said:
Very nice work. How does it sound compared to before? I want to do my 8100 but I'm wondering if I should since it sounds pretty good as is. Suggestions?

"Before", the thing was as scratchy as hell, the volume control especially, and the tone control didn't work at all.

If the 8100 is anything like the 7100 in it's construction, then it should be a pretty easy amp to recap. It all depends how confident you are doing it, and whether you plan on keeping it for a long time.

Lee.
 
"Before", the thing was as scratchy as hell, the volume control especially, and the tone control didn't work at all.

If the 8100 is anything like the 7100 in it's construction, then it should be a pretty easy amp to recap. It all depends how confident you are doing it, and whether you plan on keeping it for a long time.

Lee.

I meant before you recapped it not before you cleaned it. All my amps were all a little scratchy before deoxit, but I want to know how it sounded original vs recapped. My 8100 is original and sounds excellent.
I do greatly enjoy my 8100, I'd like a 9100 to go with it. I probably will keep it quite a long time.
 
Leesonic,

Did you make up the trimmer pots VR3 & VR4 with the three legs spread like that? I need something like it for my 9G. What trimmers are those?

Mike
 
captaingamez said:
I meant before you recapped it not before you cleaned it.

That's always impossible to tell unless you do an A/B comparision on them. Maybe if another one comes along cheaply, I'll audition them together. Or perhaps I should start an eBay business doing these, I see this kind of thing for other amps?

mikte15 said:
Did you make up the trimmer pots VR3 & VR4 with the three legs spread like that? I need something like it for my 9G. What trimmers are those?

They are just Bourns 3296Y trimmers with an extra piece of wire soldering on to the center leg. Mouser part number is 652-3296Y-1-501LF for these 500 ohm ones.

Lee.
 
Thanks for the great pictures (again!). What did you use for replacement transistors - I have a 7100 I am planning on recapping.
 
They are just Bourns 3296Y trimmers with an extra piece of wire soldering on to the center leg. Mouser part number is 652-3296Y-1-501LF for these 500 ohm ones.

Lee.

That's good to know. I guess the easiest way to do this is to snip the lead closely to the trimmer body and then desolder the other legs. Lift it a little from the top side of the board and solder the new trimmer's lead to it. I'll be using the Murata ones...25 turn 500ohm...about $1 cheaper each.

I'm assuming that you measured the ohms on each leg of the ones you removed to "preset" the new ones going in so that you'd be in the ballpark when powering up correct?
 
Thanks for the great pictures (again!). What did you use for replacement transistors - I have a 7100 I am planning on recapping.

Which ones? The tone control transistors are KSA992 and KSC1845. The relay driver transistor is KSD1616.

Lee.
 
Yes, those are the ones...I recall reading discussions on Q34 especially and wasn't sure what a good available replacement is.

Which ones? The tone control transistors are KSA992 and KSC1845. The relay driver transistor is KSD1616.

Lee.
 
lee - I am curious about the heatsinks you added to those two transistors in the power supply.

are those mouser parts? are they mounted with a special screw/nut? it appears that there may be some type of thread lock compound applied to them, is there?
 
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