nashou
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Post by nashou on Mar 27, 2019 16:33:37 GMT -5
LED fuse lamps came in as di the Coupling caps and the main Rail cap. those are sexy !!
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nashou
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Post by nashou on Mar 26, 2019 21:18:26 GMT -5
Using Mousers selection options it comes up as a 2n4124 as an exact replacement with the same parameters. But says they are on order. Of course you can exceed some parameters and get a whole bunch more options it is just harder to narrow down. Yeah, i saw that thats why i was looking for others, and here I think Id like to use a lower noise part. The way the through holes are laid out on the board adjusting the legs to their correct locations will not be hard. Also the existing c900 have a insulator on one leg I can move over incase the legs get too close for comfort. Nashou
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nashou
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Post by nashou on Mar 26, 2019 19:53:04 GMT -5
What is a good replacement I think i read some where the KSC1845's? Nashou There are a lot of various replacements. But you have to watch for leg placement. Your cross does not match leg placement to the 2sc900. Just looking around and the Ic is too low with the KSA1845, here is the 2SC900 Data sheet the 1845 has 50mA Ic the c900 has 100mA , but the package is reversed so I'd just have to put it in backwards if I was going to use it. the BC550 I think would work better but then id have to watch leg placement. These are said to be low noise. I started a thread on AK about what small transistors to keep in stock . What else would be good? Looking on mouser now. I want to place an order with a crap load of different transistors and more caps in one order so I'm not constantly wasting money on shipping. plus I hate waiting for parts, it be nice to have most common parts on hand if I'm going to be doing more vintage repairs. nashou
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nashou
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Post by nashou on Mar 26, 2019 8:08:22 GMT -5
One thing I realized, now looking back, that may have been an issue was using my iPhone for testing. I can't remember if I had the volume all the way up on the phone when I noticed the distortion. Because after the re cap I had the volume at mid point on my iPhone. I turned it up to full and i got distortion again. So I think the input limit on this amp is not tolerant to high voltage input. I need to look up max output voltage on the iPhone. And I wonder what the max input voltage is on the pre amp? But I think I might change those two 2sc900 transistors that drive the LD 3120's . because even with no input turning volume up I still get noise, just down about 80% than before the re cap. What is a good replacement I think i read some where the KSC1845's? Nashou
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nashou
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Post by nashou on Mar 25, 2019 19:28:48 GMT -5
Gotcha , Well I have the lights coming for this and i decided to get some nicer coupling caps for the two outputs and the main power cap, the 2200uf 63 volt. I went up to 4700uf and 80 volts Nichicon LKG1K472MESCBK and on the output caps I went to 50 volts and 3300 uf Nichicon LKG1H332MESABK . Might help a bit maybe?
Been playing for about 20 minutes and sounding better as it settles in I think.
Nashou
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nashou
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Post by nashou on Mar 25, 2019 19:05:59 GMT -5
Sounds much better !!! Still some back ground noise with no input and volume turned up. Might be those 2SC900's or maybe that other board is in play . I'll need to do some tracing of the inputs . But the re cap helped a lot or it may have been the pots being cleaned and worked more than I did before . I did not change any of the ceramic caps, I wonder if that might make any improvement, if I choose the right ones to replace. I have some of the 101's ( 100 pf) in silver micas I think. and maybe some others in film.
Oh and the HUM is still there but maybe not as loud.
Nashou
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nashou
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Post by nashou on Mar 25, 2019 18:54:42 GMT -5
Never mind, found the data sheets and max is 1000 hFe so we're good here.
Nashou
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nashou
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Post by nashou on Mar 25, 2019 18:46:36 GMT -5
Sounds good. Oh one thing i noticed and forgot to mention in previous post. The two transistors are 2SC900's . I pulled one and tested it and saw the highest hFE i have ever seen on a transistor. is this normal for these?
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nashou
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Post by nashou on Mar 25, 2019 18:13:13 GMT -5
I have no idea of other boards. But what I can say is by using the above schematic and if you could put together an audio signal tracer like I posted in the audio section you could test at a few points and see if the noise is there or not and probably trace around to see where it is being introduced. Yeah thats the hard part. that board is buried under the front panel making it hard to probe and test. But I re capped it anyhow since I had all the caps, except for some 10uf i went with 22uf as I have a crap load of those. The .47uf caps had 45 ohm ESR !! And most caps were all way higher than the ones I replaced and the values were all almost doubled or 1.5 times more than what they were listed as. I also sprayed WD-40 into the all the pots and turned them about 25-40 times each . So At this point I'll solder the board back in maybe with jumper wires so If I do need to hook up my scope and a 1 khz signal ( my one LCR meter does that) I can look for the noise then. I'll report back once I get it rigged up. Nashou
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nashou
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Post by nashou on Mar 25, 2019 13:08:47 GMT -5
Reference only. Thanks Mac, I've looked for noise issues others may have had with that part, but have not seen it discussed. Do you have any experience with that part? Also What is that other board, the smaller board , the one under the metal cover? Equalizer/Phono board? Nashou
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Post by nashou on Mar 24, 2019 21:49:39 GMT -5
one part on the board is a Sanyo LD3120 Integrated Circuit 9 Pin ZIP audio preamplifier with equalizer Replaces ECG1019 What is this part for? Is is then the preamp board ?
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Post by nashou on Mar 24, 2019 21:37:44 GMT -5
unless this is it, under the silver box in the one photo of the entire amp .
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nashou
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Post by nashou on Mar 24, 2019 21:32:20 GMT -5
Also remember distortion and/or scratchy can be volume control needs cleaning or even any other manual control or switch. Yes, i am going to go through that as well. Thought I did clean them well as adjusting them while playing amp I heard no scratchy doing than. But I did on the Tape monitor switches but not too bad. I think what I removed is more of the tone board. have to look for other boards that might be the pre amp, or maybe this is it?
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nashou
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Post by nashou on Mar 24, 2019 21:04:43 GMT -5
You are welcome. When you say with no input, did you try with the preamp/amp jumpers removed? Some hum may be normal in this type amp. Is the AC plug 2 prong? Yes jumpers removed , and it is a two prong plug. nashou
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nashou
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Post by nashou on Mar 24, 2019 20:19:52 GMT -5
Well I skim read that article and found nothing surprising. As far as your questions I have no specific answers. You still don't even know what those pots are really adjusting. You keep saying bias but there has been no prof of that. I don't know what they are adjusting only that you are reading some changes at a location. But it sounds like it is working. What seems to be the problem? I figured out why it didn't sound right and had distortion. Something in the pre amp section. I decided to use my iPhone as the preamp . No distortion at all and the amps in here sound really good even with the iPhones crappy pre amp. So now I am going to take that out and check transistors and caps etc. ugh more work but also more learning!!!! I love learning and You Mac are a great teacher. Thanks so far So now off to start removing the preamp board. And to do that the whole from needs to come off to get to it. Thing I hate about pre amp boards is all the parts connected to them. Any suggestions as to what parts to check first? Probably the transistors correct? With the volume up at higher volumes with no input you could hear two things. Hum that would get louder as volume increased and the same with just scratchy noise or distortion. Athanasios
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