Vintage Integrated Amps: KA-5700, KA-7100

[hopjohn]

I've primarily used the KWs as above but also KGs. I'm going from memory but I've used both the 10000uf 50v and 6800uf 63v. I think it runs around 48v so 50v is a bit close. These are all 12.5 mm leaded. The holes are 15mm LS but wide enough to allow. If I've ever widened the holes it was only just slightly. I don't know of anything better to use, and believe me I've looked.

Edit: Forgot to say that I've used FWs as well.

 

[roger2]

Now I recall that I also used KW's with (I think) 12.5mm lead spacing. Memory isn't what it used to be. I did have to alter the holes a bit with a sharp blade (exacto type knife).

My rails measured about 46.5V and I did use 50V, 10K uf. But I would recommend to anyone making decisions now to use 6.8K uf (or maybe 8.2K uf if available) if they don't plan on improving the main power switch in some way.

Mainly, I just wanted the OP to be aware that some modification may be required to the PCB to get new main filter caps to fit.

 

[hopjohn]

My rails measured about 46.5V and I did use 50V, 10K uf. But I would recommend to anyone making decisions now to use 6.8K uf (or maybe 8.2K uf if available) if they don't plan on improving the main power switch in some way.

That sweet little triac mod is useful. I use it all the time on the 7100 and more.

 

[gort69]

This was on sale at parts express so I figure I'll try it:
http://www.parts-express.com/ecg-j-045-ds-45-watt-desoldering-iron--372-202

Thanks!

That's the tool that I use. Once you get the hang of it, it works really well. Just get in and get out quickly - it's pretty hot, and you could damage solder pads. If you use it a lot, you'll go through some tips. I've recapped what are considered fairly difficult units with just that for 99% of the desoldering. Make sure you squeeze the bulb before you go in, and empty after each solder joint. (I just empty it on the garage floor and sweep up) If you forget to empty it and forget to squeeze first you'll spray molten solder all over the board - not the best scenario. Once in a while I've used this https://www.radioshack.com/products/radioshack-pro-line-desoldering-pump. I have some solder wick, but hardly ever use it.

The one KA-7100 I did I'm pretty sure I used the UKW 6800uf caps and don't recall doing any enlarging of the holes.

I agree with Roger on the switch. I'm currently working on a KA-9100 which uses the exact same switch as the 7100. The 9100 has 4 x 12,000uf caps - the switch in this one was TOAST.

Hopjohn gave me a great tip on removing the glue. Soak with acetone using a q-tip and scrape with a sharpened (beveled) popsicle stick from a craft sore. Slow going, but the wood won't scratch the board.

 

[hopjohn]

I use the reamer in a kit like this for cleaning up the holes or making them a touch larger if needed.

 

[roger2]

@gort69 - Does the power switch in KA-9100 use both sides of the power switch?

In the 7100 and (I believe) the 8100 only one side of the switch is utilized. In my 7100 I cleaned up the switch contacts then jumpered the switch so that both sets of contacts were in use.

 

[gort69]

No - just one side. And as you know, really uses just one of the four available contacts.

There's a guy from Taiwan on this one particular well known, often maligned yet very handy website that we all use from time to time who sells brand new "Alps 6 pin toggle switch"es cheap. I have use a few of them to overhaul these switches a few times by swapping the new body onto the original toggle.. On this one I just flipped the body 180 to the unused pair and bridged it as you did.

 

[hopjohn]

I have use a few of them to overhaul these switches a few times by swapping the new body onto the original toggle..

Did you break the body tabs? I'm always concerned with that possibility.

I thought @gort69 @roger2 that you guys would've adopted the triac by now. No more inrush, no more worries.

 

[gort69]

No - those tabs are pretty tough. Of course there would be a limit to how many times you could do it. I bet it would take it several times to finally break.

I was gonna do the triac on this one, but Mouser doesn't sell them(that I could find). Next time I order fom DigKey I'll get a few, and go back in and do it. I've done a few 9600s and 7600 with relays. That extra click is pretty cool, but it is a lot more work than the triac.

 

[hopjohn]

That extra click is pretty cool, but it is a lot more work than the triac.

Yea, it kinda is and it kinda is.

Q6030LH5 should be back in stock around 3/10/17 according to Mouser.

 

[claneg]

Thanks claneg. I think that is the same part that is referenced in leesonic's list. I appreciate the help!

You are right, my mistake! I was thinking at VR series: 647-UVR1J682MRD. Same dimensions as KW but general purpose; however VR has a better ripple current than KW, which is worth in a power supply.

 

[fromnowon]

I just wanted the OP to be aware that some modification may be required to the PCB to get new main filter caps to fit.

Thank you, roger2.
What kind of glue do you guys use to attach the new capacitors? I really appreciate all the help.

 

[hopjohn]

Thank you, roger2.
What kind of glue do you guys use to attach the new capacitors? I really appreciate all the help.

I use Permatex RTV Clear Silcone adhesive. Just a tiny dab'll do ya.

 

[fromnowon]

I use Permatex RTV Clear Silcone adhesive. Just a tiny dab'll do ya.

thanks hopjohn!

 

[fromnowon]

Hello,
I'm able to reference everything in leesonic's list for the power supply caps to my service manual, except I'm not sure about this one:
Per Lee:
bypass caps for mains 4 x 1uF film 5989-100V1.0-F, which is this:


Is that Ce35-38?


Thanks very much. I sincerely appreciate all the advice.

 

[hopjohn]

The bypass caps are added items and aren't stock on the unit. They are meant to be placed across each of the large filter caps. There's no polarity for film caps, so just install them with the printed values showing and do so at the same time as the main caps in order to make a mechanical connection.

 

[fromnowon]

The bypass caps are added items and aren't stock on the unit. They are meant to be placed across each of the large filter caps. There's no polarity for film caps, so just install them with the printed values showing and do so at the same time as the main caps in order to make a mechanical connection.

- Oh! Thanks again hopjohn. I can't find any pictures of that mod. Does this help the sound significantly?

So absent a picture, do these bypass film caps just go between the + and - leads on each respective 6800 uF filter cap then the leads on the bypass caps are long enough to bend them up along the side of each filter cap?

 

[hopjohn]

Read posts #81 - #84

 

[fromnowon]

OK, thanks that helps.

From that picture it looks like the film caps will be attached to my leads on the bottom side. That makes more sense now.

"The film caps keep impedance low even at high frequencies." Somehow it seems logical that this will help with low end, I think.

BTW, I ordered 6,800 uF as in the original list leesonic posted. All the parts were available for power supply and very cheap except the filter caps. I think roger2 used 10,000 uF so i hope I made the best decision there; my relay and power switch seem fine so I don't plan to mess with that now.

I'll try 6,800 uF filter caps with the film caps strapped across the leads attached beneath the PCB.

Thanks again.

 

[roger2]

FWIW, the use of poly bypass caps across main filter caps is an issue about which there is no consensus. If anything, some of the more recent thinking is that they are not needed to improve impedance characteristics of modern caps. This topic has been debated in depth over at DIYaudio.com, which is quite a different place than AK. Discussions over there get extremely in depth technically, and can run hundreds of pages long. There are even some compelling arguments against bypassing main filter caps, in particular by a poster who goes by screen name Eva.

I have read much of that discussion (well, at least what was posted up until a couple years ago), and came away with the feeling that, not having the ability to test adequately, I would simply not install bypass caps. YMMV