My new KA-3500. Re-cap.

Hey guys.
I am stoked to finally get my vintage Kenwood integrated amp. Sounds really pretty decent.
I'd like to get the most of my new gear so I am going to be gathering parts for a recap of all the electrolytic capacitors.

One of the reasons I am moving from a receiver to an integrated amp is that there is a lot less parts, and the KA-3500 fit the bill perfectly.
A lot less caps to replace in this thing than there were in my Concept receiver.

Below is a list of the capacitors that the parts list has in the service manual:

Amplifier section
(1) .47mf 50v - Nichicon KW - Mouser
(1) 47mf 10v - Nichicon VP - Mouser (or Elna Cerafine)
(1) 47mf 50v - Elna Silmic II - Handmade Electronics (*Black Gate available)
(1) 47mf 100v - Elna Silmic II - Handmade Electronics
(1) 100mf 10v - Nichicon KW - Mouser (or Elna Cerafine)
(1) 220mf 10v - Nichicon KW - Mouser (or Elna Cerafine)
(1) 220mf 50v - Elna Silmic II - Handmade Electronics (*Black Gate available)
(1) 330mf 35v - Nichicon KW - Mouser
(1) 330mf 16v - Nichicon KW - Mouser
(1) 6800mf 42v - Can't find one of these anywhere

Pre-amp section
(1) 1mf 50v - Elna Silmic II - Handmade Electronics
(1) 3.3mf 50v - Elna Silmic II - Handmade Electonics (*Black Gate available)
(1) 4.7mf 35v - Nichicon ML - Mouser
(2) 10mf 25v - Elna Silmic II - Handmade Electronics
(1) 47mf 16v - Elna Silmic II - Handmade Electronics
(1) 220mf 35v - Nichicon KW - Mouser
(1) 22mf 10v - Nichicon ST - Mouser


Without opening up the cabinet I have not yet measured the caps that I have selected to see if they will fit although I have seen pictures of the inside of the cabinet and it looks like there is lots of room.
The other thing I am not sure about without opening the cabinet is whether or not some of these caps are bi-polar.

Can't wait to get started.
Does the list above seem to be going in the right direction as far as brand, etc.?

Go up in voltage for the one you can't find.
Not knowing where in the circuit, but if in the audio path many replace the <1µF units with poly film caps

Blue Shadow said:

Go up in voltage for the one you can't find.
Not knowing where in the circuit, but if in the audio path many replace the <1µF units with poly film caps

Click to expand...

I just updated the post above with the section applicable.
Thank you for any input.

Okay, Elna does make a 6800mf 50V cap.
If I substitute a 50V cap for the 42V called out in the service manual will I fry anything, or are there any negatives to doing this?

It'll be fine. The problem is that the pin layout for the new caps is pretty unlikely to match the original (if the original is a snap-in, or a tri-mount). You might have to get creative.

I have a rebuilt 3500 here driving my Heil's in a biamp setup, but I left the big PS caps alone.

That tells a lot.:yes:
Did you replace all the other Electrolytics?

Oh yes. I also added offset adjust, a protection circuit w/relay, and opamp buffered pre-out/main-in jacks. But that's getting carried away.

A great little amp you have there, well worth fixing up. I had one for nearly 30 years that I bought new in 1977.

And it looks so purdy in the walnut cabinet.
Now I just need the matching KT-5300 to go with it.:thmbsp:

EchoWars said:

Oh yes. I also added offset adjust, a protection circuit w/relay, and opamp buffered pre-out/main-in jacks. But that's getting carried away.

Click to expand...

Wow. That's awesome!

Let me ask you guys this.
In the list on the original post I pointed out where Black Gate caps were available.
Do you think these are really that much better than Silmic II's?
For consistency's sake I could see keeping with mostly Silmic II's and Nichicon.
Also, there are Cerafine's available instead of the Nichicon's.
Any ideas which ones would be better?

No, they aren't.

For Cd17 & Cd18 in the preamp, and Ce1 and Ce2 in the power amplifier, use a 1µf 50V Panasonic Stacked film #P4675-ND from Digikey. For the rest of the signal path caps (Cd11, Cd12, Cd23, Cd24), the Elna Silmic II's will be more than good enough (use a 4.7µf 25V for Cd11 & Cd12). The rest of the caps can be Nichicon PW or HE, or Panasonic FC or FM. No, I don't know what the Mouser equiv. is, as I deal with Digikey 99% of the time.

Ce7 and Ce8 on the power amp ought to be replaced with 220µf 10V.

Bias pot question.
In the service manual it says to measure voltage across the emitter resistors.
Got that.
There is a pot for the left an right channel, so do you adjust both pots until you get 40mV across the emmiter resistors?

Two pots...one for each channel. One gets adjusted, and then you have to move the meter leads to adjust the other.

Take note...the output devices in the 3500 are unobtanium, and replacing them will be an unnecessary PITA. If you are going to try and adjust the bias, read below:

The point contact leads shipped with most meters is the cause of more blown amps than I care to count here at AK. Tuck them in a drawer somewhere and forget about them. Here are Pomona Minigrabber leads, and this is what you shall use. Digikey PN 501-1060-ND for 48" black, and 501-1061-ND for 48" red. Every meter you own should have a set of these.

Click to expand...

From here.

Oh yeah, I've read and re-read.

So, one channel you measuere voltage across Qe21 and Qe23 emitter resistors, and the other channel you measure voltage across Qe22 and Qe24 emitter resistors?
I suppose Qe21/Qe23 is the the pair that adjusts the left channel?

Thank you, thank you EW.:

EWizard said:

So, one channel you measuere voltage across Qe21 and Qe23 emitter resistors, and the other channel you measure voltage across Qe22 and Qe24 emitter resistors?
I suppose Qe21/Qe23 is the the pair that adjusts the left channel?

Click to expand...

Yes on both counts.

Thank you again.
That's all I have for now.:thmbsp:

Power off, connect to the emitter legs of the transistors directly with the mini-grabber leads...or if that makes you nervous, study the schematic so you can identify the sides of the emitter resistors that are connected to the emitters and connect to the legs of them (there's usually a bit of lead showing between the resistor and the PC board). Power up, adjust one side, monitor the voltage reading for a good 30 minutes and readjust as necessary, and power down before you move the leads to the other channel. You do want to be careful here, as replacing those output transistors will be a serious PITA and you'll be kicking yourself for having to do it.

I gotta say, this amp ROCKS!!!
Really hard to believe it is only 40 watts per channel.
It's freaking loud when the dial is a 3.5!

The sound is good now, so I can't wait to see what it sounds like with all the e caps replaced.

Catalogs are your friend, search engines are a bitch.

For your PS caps, I went with Nichicon VZ caps and bypassed with the Panasonics

Nichicon 6800uf, 63v.....Digi-Key p/n 493-1363-ND

Panasonic 2.2uf, 250v...Digi-Key p/n P10983-ND

These are for your amps' bigger brother, the KA-7100. I had one like yours for a spell and shouldn't be any problem. Had no fitting issues on my amp.

Good luck and happy listening!