Kenwood KT-7500 recap and upgrade

[leesonic]

Just thought I'd post some picture of my Kenwood KT-7500 re-cap and upgrade. The plan was to replace all the electrolytic capacitors on the board, but then I got reading the DIY section over on FMtunerinfo, and so I decided on doing some of the upgrades as well.

Here are pictures of the board before I started.





And here are pictures after I replaced the caps. I used Nichicon KWs throughout.







Here's where the upgrades start. This picture shows extra decoupling capacitors across IC6...



...which has been replaced with a gold plated socket containing an OPA2604



One big modification was to remove the 110v AC from the board. I also mounted the transformer on rubber grommets to isolate it from the chassis both mechanically and electrically.





Lee.

 

[miklemke]

Really nice photos.

Could those decoupling caps be mounted on the other side of the board?

 

[thefragger]

Did you listen to it after each mod? I'm curious about how the sound 'evolved' with each step... :scratch2:

 

[JBL GUY]

Nice work!

Tell how it sounds with your upgrades.

 

[CohibaJoe]

WOW...I also just picked up a KT-7500 and just ordered my caps and Films.
I also got the bug to do this Mod at FMtunerinfo.

Another site for Mod..http://sites.google.com/site/mpbarney/kt-7500tuner

I also with be replacing the caps with either Elna Silmic II, Nichicon KZ or FG...still thinking it over.

1. Power Supply Upgrade caps Mod per (FMtunerinfo).
2. Op-amp mod with OPA2604 and/or LME49860NA...another user said the LME49860NA sound better...so I got both to try out.
3. Film relpaced Mod

That's it for me...Will let you know this goes...

 

[EchoWars]

Use an opamp with low enough offset and you can replace Cb49 and Cb50 with a jumper wire. An AD823 would do well here.

 

[CohibaJoe]

I have completed my recap...Well Well Well.

Output Coupling C49 and C50...Following the "mpbarney/kt-7500tuner" link...had BlackGates..I used Elna Cerafine...Nice, Clean and Very Detail..
BUT...Voice on the Top End..Scratchy...not smooth at all.

So, took out the Cerafine and replaced with Nichicon Muse KZ...Well, Lows and Highs were Poor...So..replaced with Nichicon FG..

Now Lows and High are back...But without the Scratchy sound the Cerafine had. :scratch2: Just a touch of Detail is missing compared to the Cerafine.

So, I am going to put in Elna Silmic II....will follow-up.

Silmic II are in...need around 25hrs to these open up..But the Lows and Highs are nice...It will get better...

 

[leesonic]

Really nice photos.
Could those decoupling caps be mounted on the other side of the board?

Thank you. I probably could have found somewhere to put those caps on the other side, but it would still have looked kinda strange. I glued them to the board with a hot melt gun and then soldered them.

Did you listen to it after each mod? I'm curious about how the sound 'evolved' with each step... :scratch2:

I wish I had an FM transmitter or something to inject a signal straight into the tuner. FM radio is so dire where I live, that the tuner got used for background music.

Nice work!
Tell how it sounds with your upgrades.

Thank you. See comments above.

I sold this tuner last month, I hope the new owner is getting some use out of it.

Lee.

 

[Robinhawaii]

Looks good Lee. Are you going to remove the de-emphasis switch and use two jumper wires? "For 75 µS add a wire between standoffs 28 and 29 and between standoffs 26 and 27."

 

[leesonic]

Looks good Lee. Are you going to remove the de-emphasis switch and use two jumper wires? "For 75 µS add a wire between standoffs 28 and 29 and between standoffs 26 and 27."

Yeah, I did that before I sold it.

Lee.

 

[leesonic]

Fixed dead picture links. I've also learned a lot since doing this one. WIMA films or Nichicon KLs should be used to replace orange Elna caps. And a VX series cap is fine for the big axial cap in the power supply.

Lee.

 

[leesonic]

Looks good. Wondering if you've tried that negative voltage regulator that they mention? There seems to be no lack of mods for the 7500 series. That was one of the deciding factors on going with Kenwood gear..along with all the documentation and info all over the net. Had a similar vintage Kenwood transceiver a few years ago that was equally nice to work on.

Yeah, I did it in this one :

http://audiokarma.org/forums/index....green-leds-power-supply-upgrade-recap.457960/

Like I said, these things are like a learning curve, every one you do you figure out something else.

Lee.

 

[8xlaxx]

Fixed dead picture links. I've also learned a lot since doing this one. WIMA films or Nichicon KLs should be used to replace orange Elna caps. And a VX series cap is fine for the big axial cap in the power supply.

Lee.

Very helpful post @leesonic Thank you for your suggestions regarding the caps!

 

[8xlaxx]

Awesome pics too!

 

[Lefty314]

Hello Lee and others. I'm going to perform some mods on my KT-7500. Just a recap and OPAMP upgrade to start. Can anyone tell me what the values of the decouple caps should be?

Thanks!

Bill R.