Project: Kenwood KA-3500 (Nate Dogg)

[Super Noob]

Well - here goes another rebuild thread. In the last month or so, I succumbed to pressure applied from that other person living in my house. I listed a few of my pieces for sale locally on my wifey's face space marketplace. Needless to say, we didn't get much interest in the pieces listed; however, I did get about 10-15 people looking to hire my services for repair. You know I ain't going out like that. Not too many people out there are willing to challenge themselves to a vintage rebuild. One message came across was from a local cat named "Nate". We will referred to him as Warren G's side kick = Nate Dogg (RIP to the original Dogg).

Basically Nate Dogg indicated that he had a boat anchor that he was getting ready to move to the curb. The boat anchor's nameplate indicated KA-3500. If I had interest, the rig could be secured for FREE.99

The only thing better than a dirt cheap non-working rig is a free non-working rig. The bench is clear so all you "skirts know what's up" next.

Many folks ask me what's my favorite brand might be.... my favorite brand is 1970s (that is a brand isn't it?) Maybe it is just the smoothness of the large advents in my work area, but pretty much everything from this era just turns out great with a little love. Kenwood is no doubt one of the quality brands from the 70s that should not be overlooked or taken lightly.

A very nicely documented build was done by no other than our favorite grey face @hopjohn
https://audiokarma.org/forums/index.php?threads/the-ka-3500-restoration.840144/
His work and builds are always nicely done and documented. Big shout out to Hippity Hoppity Johnnity.

Know that I rebuilt KA-8100, KA-7100, KR-8050, KR-8010, 9G previously... so here goes my build on the KA-3500.

Here is how she landed in the garage.

Lets look inside...

Holy smokes this is straight up nasty = perfect. Too late to put the cover on and pretend like we didn't see that.

 

[Super Noob]

This rig has no protection circuit - speaker coils beware. Fire it up on DBT... and lets look at the offset.

Bad

Worse

Visual inspections imply issues with power supply, but lets start with easy boards. This rig is not easy work on / as well is it not hard to work on either. Will say it is simply not for beginners or for those that scare easily.

PreAmp Unit (X08-1530-00)
Cd1 Electrolytic 22uf / 10v Electro 22uF 10v UKA1E220MDD Nichicon 22uF 16v (UKA)
Cd2 Electrolytic 22uf / 10v Electro 22uF 10v UKA1E220MDD Nichicon 22uF 16v (UKA)
Cd9 Electroylic 100uf / 10v Electro 100uF 10v UKA1C101MDD Nichicon 100uF 16v (UKA)
Cd10 Electroylic 100uf / 10v Electro 100uF 10v UKA1C101MDD Nichicon 100uF 16v (UKA)
Cd11 Electroylic 3.3uf / 50v Electro 3.3uF 50v UKL1H3R3MDD Nichicon 3.3uF 50v (UKL)
Cd12 Electroylic 3.3uf / 50v Electro 3.3uF 50v UKL1H3R3MDD Nichicon 3.3uF 50v (UKL)
Cd17 Electroylic 1uf / 50v (LL) Electro 1uF 50v R82DC4100DQ60J KEMET FILM 1uF 63v
Cd18 Electroylic 1uf / 50v (LL) Electro 1uF 50v R82DC4100DQ60J KEMET FILM 1uF 63v
Cd21 Electroylic 4.7uf / 35v Electro 4.7uF 35v UPW1H4R7MDD Nichicon 4.7uF 50v (UPW)
Cd22 Electroylic 4.7uf / 35v Electro 4.7uF 35v UPW1H4R7MDD Nichicon 4.7uF 50v (UPW)
Cd23 Electroylic 10uf / 25v Electro 10uF 25v UKL1V100KDD Nichicon 10uf 35v (UKL)
Cd24 Electroylic 10uf / 25v Electro 10uF 25v UKL1V100KDD Nichicon 10uf 35v (UKL)
Cd25 Electroylic 10uf / 25v Electro 10uF 25v UKT1V100MDD Nichicon 10uf 35v (UKT))
Cd26 Electroylic 10uf / 25v Electro 10uF 25v UKT1V100MDD Nichicon 10uf 35v (UKT))
Cd37 Electroylic 220uf / 35v Electro 220uF 35v EEU-FM1V221L Panasonic 220uf 35v (FM)
Cd38 Electroylic 220uf / 25v Electro 220uF 35v EEU-FM1V221L Panasonic 220uf 35v (FM)
Ce39 Electrolytic 47uf/16v Electro 47uF 16v UKA1E470MDD Nichicon 47uf 25v (UKA)

This is really two board.

Some board flux cleaning = IPA (not served at your local brewery)

Didn't get very good after pics... need to tighten up.

After I finished the rebuild, went back in and replaced the small transistors and input signal path resistors.

Qd5-Qd8 2SA640 KSA992FB
Qd9-Qd10 2SA872 KSA992FB

 

[Super Noob]

These combo boards are large, and the amplifier and power supply board didn't disappoint. There is no bottom access to the boards, so you gotta get'em up and out. Think I desoldered a few transformer wire-wrap pins from the power supply area which allowed me open her up like split roast beef sandwich.

The original main filters are long gone have looked to have given up their guts in the past. The crime scene (top of the board) had plenty of evidence still visible. The filter replacement jobbie was done by a USDA certified butcher... booger'd up traces were found. Based on the access, I went ahead and replaced all the silicon on the power supply and amp (minus the outputs)... I found good modern replacements were available in my part supply.

I forgot to mention that somewhere along the way, a large hippo took a side bite of the board. Looked like a strategic weight reduction for the most part... one large trace was reduced for aerodynamics I will assume.

Lets call this a noob fortification...

Here is some before pics:

Know it doesn't look that clean... but I worked it like spare rib with acetone, and this is about as good as I could get here.

Power Amp Board (X07-1470-10)
Ce1 Electrolytic .47uf / 50v CE (found 1uf) Electro LL 1uF 50v R82DC4100DQ60J KEMET FILM 1uF 63v
Ce2 Electrolytic .47uf / 50v CE Electro LL 1uF 50v R82DC4100DQ60J KEMET FILM 1uF 63v
Ce7 Electrolytic 47uf/10v CE Electro 47uF 10v UPW1E470MED Nichicon 47uf 25v (UPW)
Ce8 Electrolytic 47uf/10v CE Electro 47uF 10v UPW1E470MED Nichicon 47uf 25v (UPW)
Ce13 Electroylic 220uf / 10v CE Electro 220uF 10v UPW1C221MPD Nichicon 220uf 16v (UPW)
Ce14 Electroylic 220uf / 10v CE Electro 220uF 10v UPW1C221MPD Nichicon 220uf 16v (UPW)
Ce15 Electroylic 47uf / 50v CE Electro 47uF 50v EEU-FC1J470B Panasonic 47uF 63v (FC)
Ce16 Electroylic 47uf / 50v CE Electro 47uF 50v EEU-FC1J470B Panasonic 47uF 63v (FC)
Ce21 Electrolytic 47uf/10v CE Electro 47uF 10v UPW1E470MED Nichicon 47uf 25v (UPW)
Ce22 Electrolytic 47uf/10v CE Electro 47uF 10v UPW1E470MED Nichicon 47uf 25v (UPW)
Ce23 Electrolytic 47uf/10v CE Electro 47uF 10v UPW1E470MED Nichicon 47uf 25v (UPW)
Ce24 Electrolytic 47uf/10v CE Electro 47uF 10v UPW1E470MED Nichicon 47uf 25v (UPW)
Ce29 Electrolytic 6800uf/42v CE Electro 6800uF 42v (local stock - Nichicon) Electro 8200uF 63v
Ce30 Electrolytic 6800uf/42v CE Electro 6800uF 42v (local stock - Nichicon) Electro 8200uF 63v
Ce31 Electroylic 330uf / 35v CEA Electro 330uF 35v UPW1H331MPD Nichicon 330uf 50v (UPW)
Ce32 Electroylic 330uf / 35v CEA Electro 330uF 35v UPW1H331MPD Nichicon 330uf 50v (UPW)
Ce33 Electrolytic 47uf/100v CE Electro 47uF 100v UPW2A470MPD Nichicon 47uf 100v (UPW)
Ce34 Electroylic 330uf / 16v CEA Electro 330uF 16v EEU-FM1E331L Nichicon 330uf 25V (FM)
Ce35 Electroylic 220uf / 50v CE Electro 220uF 50v EEU-FM1H221 Panasonic 220uf 50v (FM)

Qe1 2SA620 KSA992FB (Vbe / HFE Match)
Qe2 2SA620 KSA992FB (Vbe / HFE Match)
Qe3 2SA620 KSA992FB (Vbe / HFE Match)
Qe4 2SA620 KSA992FB (Vbe / HFE Match)
Qe5 2SC1885 KSC2690AYS
Qe6 2SC1885 KSC2690AYS
Qe7 2SA620 KSA992FB
Qe8 2SA620 KSA992FB
Qe9 2SA733 KSA733CYTA
Qe10 2SA733 KSA733CYTA
Qe11 2SC945 KSC945CYTA
Qe12 2SC945 KSC945CYTA
Qe13 2SC945 KSC945CYTA
Qe14 2SC945 KSC945CYTA
Qe15 2SA733 KSA733CYTA
Qe16 2SA733 KSA733CYTA
Qe17 2SC1735 KSC2690AYS
Qe18 2SC1735 KSC2690AYS
Qe19 2SA850 KSA1220AYS
Qe20 2SA850 KSA1220AYS
Qe21 2SD588 (retain)
Qe22 2SD588 (retain)
Qe23 2SB618 (retain)
Qe24 2SB618 (retain)
Qe25 2SA673A (not found)
Qe26 2SC1222 KSC1845
Qe27 2SA673A KSA1013Y

De1 - S5VB20 (packaged bridge) Local Stock Replacement
De2 - 1S2076A 1N4148
De3 - 1S2076A (not found)
De4 - 1S2076A (not found)
De5 - CZ-245 (Zener) (24v / 3W Zener) 1N5359BRLG 24v / 5w zener
De6 - CZ-245 (Zener) (24v / 3W Zener) 1N5359BRLG 24v / 5w zener
De7 - 1S2076A 1N4148
De8 - 1S2076A 1N4148
De9 - 1S2076A 1N4148
De10 - 1S2076A 1N4148
De11 - YZ-140 (Zener) (14v / .5W Zener) 1N5244B
De12 - 1S2076A 1N4148
De13 - W06B (1 amp / 100v) RL202-TP (2A / 100v)
De14 - W06B (1 amp / 100v) RL202-TP (2A / 100v)

VRe1 Bias Trimmer 1K Ohm 1K ohm 1/2 watt (single) 3386P-1-102LF (less than ideal - had to manipulate to mount)
VRe2 Bias Trimmer 1K Ohm 1K ohm 1/2 watt (single) 3386P-1-102LF (less than ideal - had to manipulate to mount)

Some after pics:

Repasted the outputs when I installed back to the large heat sink.

 

[Super Noob]

Want to see some magic...

 

[Super Noob]

Rattlesnake Shake:

Also applied some new-used shoes on her... was running on the rims for the most part.

Some Final Shots:

 

[Super Noob]

The adage that one good deed deserves another more than holds true, scientists have discovered. Researchers found that kindness is contagious and that good acts by a handful of individuals really can make a difference.

What does that mean.... this rig is going back to Nate Dogg. Hope that he enjoys. Been listening to over the last few weeks burning it in... sounds sweet. Was able to get offset in the mid 30mV(dc) in one channel and high 30mVs(dc) in other = nice improvement.

 

[dstariha]

Very nice. Clearly lots of work both electronically and cosmetically. Nate Dogg should love it.
How did you clean the back panel? And where did you use the acetone? I am a little concerned about organic solvents like that around PC boards.

Great Job, Dave

 

[Super Noob]

Very nice. Clearly lots of work both electronically and cosmetically. Nate Dogg should love it.
How did you clean the back panel? And where did you use the acetone? I am a little concerned about organic solvents like that around PC boards.

Great Job, Dave

Davey... here is the deal. I used brasso to polish the back metal. Acetone is a bit aggressive = we agree, but I am not drenching just applying to the stubborn funk on the face of the board. I use high concentrate ISP for most all cleaning except for those low IQ spots and assembly glue... acetone can damage silicone / plastics / and PCBs too.

 

[dstariha]

I have a repair job on a dirty piece of equipment. I have been putting it off because I dreaded cleaning it. Your method may be enough to make me move.

Thanks

 

[The Fuxtor]

Always a pleasure reading your posts Noob!

 

[PatMorgan]

TRIO KA-3500- I enjoyed the read, but Im not looking forward to attacking my one.
I have the devastation of failed 6800 cans and 34 dc across my speaker-could, killing them. Ok, only one channel went, but Im not tearing it apart and just doing the outputs, as Im sure the drivers will be toast. These amps have a lovely sound-better than the Leak Stereo 70 that Ive put in its place. It also has sentimental reasons to get back working, as my son bought it for me about 6 years ago on the basis he had spotted a 'Trio' amplifier on a fe of our old family photos, before we had kids, back in 1980. I paid £25 for my KA-1500, from memory. I didn't ask what Justin paid for the 3500 but I did say to him that it was the 'next one up' from what we had back then!

 

[Bolero38]

This thing sat for a year after I goofed up adjusting the offset and shorted the mains with my probes. It also had intermittent very loud crackle & pops while operating undisturbed - so annoying. While looking for someone who could fix it, I stumbled upon this thread and thought might as well do it myself and learn something new in the process. With many out of stock and obsolete items, I had to source the parts from multiple places...yes, some from eBay too. THANKS SUPER NOOB!

 

[Bob Chieldon]

Well done super Noob, a man after my own heart.

 

[cordes]

Thanks a ton for the thread OP. I discovered this site after receiving an amp from a school that was going to throw it way a after it sat dormant for decades. I bought the matching tuner and simply replaced all of the capacitors. It now sounds awesome and I couldn’t be more thrilled.

Thanks again!

 

[rickl]

Thanks a ton for the thread OP. I discovered this site after receiving an amp from a school that was going to throw it way a after it sat dormant for decades. I bought the matching tuner and simply replaced all of the capacitors. It now sounds awesome and I couldn’t be more thrilled.

Good job getting your 3500 working! These amps can sound great. I have a 5700 in the living room. these are very similar to your 3500.

Enjoy the music.

 

[raycarr00]

accidentally ran into this thread while looking for pics on how to reassemble same unit(board rail...one has insulation(front-L), other, none(f-r)...OMFG! I lucked out on my unit...it just needed a bridge rectifier...it's like new! dc on spkrs is -0 and like 6. great job and effort!

 

[Bourbski]

I am new at this hobby. Watching tons of videos, bought the tools. the technician I bought the amp from had replaced the dead 6800 uF 42V capacitors with 5600 uF 50 v ones . So i figured that was not a good fix. But when I replaced them with new 6800 uF 50V capacitors , I got a hum/buzz in the speakers. The original capacitors are 3 pins. The new ones are two pins. I read that the third pin is a dummy but I wondewr if it is also a ground ? How do I fix that problem ? I re-installed the the 5600 uF capacitors. The hum-buzz is gone. I am getting very bad dc output reading (over 150 mV) . The bridge rectifier is okay. I guess I am doing many things wrong.