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Metal Film Replacement Resistors [message #10515]

Sun, 22 February 2009 22:37

77Pbass
Messages: 18
Registered: February 2009

Junior Member

Anyone have a source for Metal Film Replacement Resistors that you like? I am tweaking a K200B-1 trying to eliminate noise.

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Re: Metal Film Replacement Resistors [message #10518 is a reply to message #10515]

Mon, 23 February 2009 11:13

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

First off, welcome to the board.

I get them from Mouser in Texas. They have a great selection and ship same day, so for me I get orders from them in 2-3 days.

I know in another thread that you are looking for schematics for your amp, I saw the pre-amps posted over at ampage. Try searching there. If I get a chance, I'll try to post a link.

Again, Welcome!

Bill

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Re: Metal Film Replacement Resistors [message #10521 is a reply to message #10518]

Mon, 23 February 2009 11:27

77Pbass
Messages: 18
Registered: February 2009

Junior Member

Thanks for the welcome and suggestion. I got the full schematics faxed to me by another member.

Regarding using MFR's, I see their tolerance is much tighter (1% vs. 10%). does this matter?

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Re: Metal Film Replacement Resistors [message #10523 is a reply to message #10521]

Mon, 23 February 2009 12:00

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

No the tolerance does not matter as long as the basic value is correct. I would suggest starting with the pre-amp boards and then do the power amp board.

I was surprised at the difference that changing a few resistors and a few caps made in terms of the background noise and hiss levels. Even though you will notice a difference don't expect the amp to be dead silent.

For anyone that needs the schematics for the PC105 pre-amp board or the PC703 power amp board here's the link.

<a href="http://music-electronics-forum.com/showthread.php?t=11494" target="_blank"></a>

[Updated on: Mon, 23 February 2009 12:02]

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Re: Metal Film Replacement Resistors [message #10529 is a reply to message #10523]

Mon, 23 February 2009 13:39

77Pbass
Messages: 18
Registered: February 2009

Junior Member

yeah...that's exactly what I am going to do after reading copius amounts of posts by those who have gone before me.

I don't expect total silence but I believe I can reduce the waterfall to a trickling creek.

Thanks for the link to the schematics. I found others on that board but had Boost instead of Bright...those PDF's are good as the values are very clear.

I was reading elsewhere that you can upgrade the Output Caps and Bridge Rectifier(?) to get more headroom and possibly volume. I may tackle that after tweaking the pre-amp.

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Re: Metal Film Replacement Resistors [message #10530 is a reply to message #10529]

Mon, 23 February 2009 13:49

C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...

Senior Member

Just make sure the voltage rating is the same or higher. I generally install caps that are 2 to 4 times larger. For a 2500uF I would put in 10,000uF. Typically in K100's. Or for 4700uF I would use 15,000 to 20,000uF. You might change the AGC3 fuse to a slow blow fuse. I generally don't change the bridge. That brige is very beefy as it is. But a 200VDC 25Amp bridge should be large enough.
Conrad

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Re: Metal Film Replacement Resistors [message #10533 is a reply to message #10530]

Mon, 23 February 2009 15:44

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Changing out the filter caps and upgrading the bridge rectifier will help to get the most usable sound out of the amp, but it will not get more power from the amp.

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Re: Metal Film Replacement Resistors [message #10534 is a reply to message #10515]

Tue, 24 February 2009 06:15

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Making a bridge out of fast recovery diodes(freds) will take some switching hash ( noise) out of the amps idle noise floor that is mistaken for hiss.

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Re: Metal Film Replacement Resistors [message #10537 is a reply to message #10534]

Tue, 24 February 2009 10:12

77Pbass
Messages: 18
Registered: February 2009

Junior Member

Which part number on the PC703 Schematic is the Bridge Rectifier? CR702?

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Re: Metal Film Replacement Resistors [message #10538 is a reply to message #10537]

Tue, 24 February 2009 11:52

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

No, it isn't shown on the PC702 drawing. It appears on the overview page that shows the pre-amp boards and the power supply. It is listed as CR1.

On your amp, it is bolted to the floor of the chassis. It is 1 1/2" - 2" round (at least if it is the original one) and has 4 terminals with 2 wires that come from the power transformer and a red (+) and green (-) wire that go to the large filter caps.

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Re: Metal Film Replacement Resistors [message #10541 is a reply to message #10538]

Wed, 25 February 2009 10:15

77Pbass
Messages: 18
Registered: February 2009

Junior Member

Thanks Bill. I only have the PC board schematics. The amp is all original...I spent an hour cleaning 1970 grime from the chassis.

The part you refer to is clearly visble in this photo:
http://picasaweb.google.com/77Pbass/KustomK200B102#530503703 4957960066

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Re: Metal Film Replacement Resistors [message #10547 is a reply to message #10515]

Wed, 25 February 2009 12:06

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Yes, the round item with the four wires coming off it is the bridge rectifier.
They do not make FRED type as a bridge, so you will have to make it up from 4 seperate ones on a terminal strip or bread board.
I will fax you a schematic of the power supply with the preamp, but I tryed to fax the preamp one to you yesterday and that fax number did not work, so please check it for me.

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Re: Metal Film Replacement Resistors [message #10556 is a reply to message #10547]

Fri, 27 February 2009 09:12

77Pbass
Messages: 18
Registered: February 2009

Junior Member

I'll have to get some information on creating the bridge rectifier from 4 seperate FRED's later when I tackle that part of the amp.

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Re: Metal Film Replacement Resistors [message #10635 is a reply to message #10515]

Fri, 13 March 2009 22:51

pleat
Messages: 1452
Registered: June 2004
Location: Belding, Mi

Senior Member

If it's any help, I have a bridge rectifier from a Kustom 3 monitor amp circa 1975 era. It is a little smaller in size but has the 4 tabs on it for hooking up the leads. 20.00 I looked on the schematic and it shows the power amp using 40.2 volts and I know the older K200 series shows 39.5 volts. Not sure if there would be a problem or if there is something else in the amps that regulates the proper voltage. The Monitor is a donor amp, Tranny is now in my K150 2x10 amp and the power amp board and transistors found a home in NC.
pleat

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