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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 4:50 pm 
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Hey Fred,

Thanks for the advice. I am pretty sure I was able to measure that low with it because my old man gave me a high quality DVM that was meant for automotive use. A fluke meter that costs in the $400 range. However, I will try it the way you mentioned as well.

Yes, electrolytics don't have a good shelf life so stocking up with backups is pretty much useless.

I still have to snap some photos of the boards, but they all use axial style caps so getting regular caps will probably not extend long enough from the legs to the PCB.

Is there a difference between the 85 and 105C? The amp does not get very hot and it will be in a temperature controlled room. The guy on AudioKarma who replaced it with TVA atoms that were rated for 85C worked just fine for him. I know it will cost more to get the TVA Atoms, but like I said regular caps will probably not fit right on this board and these will basically just drop in like new ones.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 6:41 pm 
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Maraakate wrote:
I still have to snap some photos of the boards, but they all use axial style caps so getting regular caps will probably not extend long enough from the legs to the PCB.

Is there a difference between the 85 and 105C? The amp does not get very hot and it will be in a temperature controlled room. The guy on AudioKarma who replaced it with TVA atoms that were rated for 85C worked just fine for him. I know it will cost more to get the TVA Atoms, but like I said regular caps will probably not fit right on this board and these will basically just drop in like new ones.
TVA Atoms will work as coupling caps but there are other types more suited for carrying audio signal such as: http://www.vishay.com/docs/42042/te.pdf


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Sun 28, 2013 3:40 am 
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105 degree capacitors last longer than 85 degree capacitors. They're more resistant to the destructive influence of heat. Test 85 degree caps located next to power resistors and regulator transistors on an ESR meter, and it will become obvious how much they degrade. i make a lot of money from the simple fact that heat kills electrolytics.

Here's the ESR meter we use at Classic Audio Repair.

http://www.amazon.com/Midwest-Devices-C ... =ESR+meter

Fred

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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: May Sat 04, 2013 8:31 pm 
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Here is the pictures.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: May Sat 04, 2013 8:32 pm 
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And yes, the one preamp board is laying out and the one cap has the lead clipped.

The one tone board is slightly messy from some flux with me testing out adding new caps.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: May Sun 05, 2013 6:44 am 
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Those black axial electrolytics are infamous!

Fred

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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: May Sun 05, 2013 7:10 am 
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heh, looks like I'll be changing them! So far the extra/input tuners work just fine but in a week or two I will replace it all with new caps and report back if the preamp channel is working properly.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Sun 09, 2013 6:29 am 
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I haven't forgotten about this, but my work recently severely cut my hours so unfortunately I do not have the money to complete the recapping.

For those interested in an update, it was acting great for awhile but sure enough two other caps started to give me trouble and those needed replaced as well. Luckily I had some random junk laying around in my parts to get me by for now but the rest are all soon to follow I am sure.

Another thing I have noticed is the two huge resistors are very hot to the touch. Refer to the schematic to the left of the transformer/coil it is the R202 and R203 resistors by the C204 and C203. The schematic says one is a 150 ohm and the other is 8.2(hard to read?)k but they appeared to be about 1.2k for both of them when I checked. Is it possible someone built this incorrectly? Both of them are very hot but does not seem to affect the output of the amp, but I'm sure it is an issue I should address as soon as possible.

If someone needs pictures I will take them.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Sun 09, 2013 6:52 am 
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Did you check them in circuit, or with one lead disconnected?

Fred
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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Sun 09, 2013 7:09 am 
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I just read the colour code brown green red silver... which would make it 150 ohm. Sorry, thought it was 1.5k.

Maybe I am just reading the schematic wrong, so I should take pictures so you can see what I am talking about. I will do this tomorrow.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Sun 09, 2013 10:13 am 
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Brown - Green - Red - Silver is 1.5k 10% tolerance.

Fred
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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Sun 09, 2013 2:23 pm 
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http://www.elexp.com/t_resist.htm says Red == 100 ohm or I am reading this wrong?

EDIT: Nevermind I see what I was doing wrong! :S Anyways, pictures to come later today.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Sun 09, 2013 9:21 pm 
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Here is a picture. The two large resistors are the ones that are getting hot.

Yes, yes, I know there's some slight slop with how I did the capacitors but I just wanted to whip up a quick solution until I can get around to finishing everything properly.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Sun 09, 2013 11:29 pm 
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That value appears to be an emitter resistor. All of the current through the transistor is flowing through that resistor if I am on target. So, if the transistor bias is off, they may get hot. But if you are driving the amplifier hard, they will also get hot.

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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Mon 10, 2013 12:06 am 
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Then maybe the bias needs to be adjusted again. I rarely have it extremely loud. It is used daily hooked up to the TV and PC but again it's probably no more than on a scale of 10... about a 2 for the volume level.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Mon 10, 2013 12:40 am 
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Well, now I probably killed it :(

My finger slipped while reading the outputs and it popped the main fuse put a new in and heard a loud hum the light came on and then it destroyed one of the main transistors.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Mon 10, 2013 12:58 am 
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I guess this is what I wil lwant to replace them with: http://www.vetco.net/catalog/product_in ... ts_id=1944

I also realized I used the wrong fuse to replace it, ugh. Either way something was bad after that. Did I likely destroy one of the transistors before the fuse incident? Not quite sure how to diagnose what got hurt after my multimeter slipped.


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Mon 10, 2013 1:42 am 
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And the 0.82ohm 5W resistor I was testing (see pictures from earlier) now reads ~230 ohms. The others read about 0.82ohms like they should. Is it possible I destroyed this resistor and that is what popped the fuse?

Would this be an appropriate replacement: http://www.mouser.com/ProductDetail/Arc ... eomwF4Q%3d


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Mon 10, 2013 1:54 pm 
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Is it reasonable to assume the zener diode near that circuit and/or possibly the large stud mount rectifiers could have went bad during the short? Should these be replaced as well?


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 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Jun Fri 21, 2013 6:04 am 
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Got most of it recapped and sadly, most of the transistors that were on the driver boards are all bad except for one. That small one was enugh to get some dim output from either board.

I still have one preamp board left to recap and the large filter caps. Once it's done I'll snap some photos for you guys to check it out!


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