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K250 diodes [message #6051]

Thu, 04 August 2005 09:44

Wattsyurz
Messages: 16
Registered: July 2005
Location: SC

Junior Member

My K250 power amp (PC5065) shorted a diode (CR4), and I can't determine it's exact voltage rating. I would guess at 80v? Also, what about the 1% tolerance on the biasing resistors? Where would you get those buggers???

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Re: K250 diodes [message #6052 is a reply to message #6051]

Thu, 04 August 2005 12:43

stevem
Messages: 4786
Registered: June 2004
Location: NY

Senior Member

I do not have a schematic here in front of me at work, but if cr4 is a crystal type diode, than it is a zener type and needs to be replaced with the same value. The 1% resistors can be ordered from mouser electronics.

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Re: K250 diodes [message #6055 is a reply to message #6051]

Thu, 04 August 2005 20:57

Wattsyurz
Messages: 16
Registered: July 2005
Location: SC

Junior Member

Thanks, I'll try Mouser for the resistor network, but the schematic doesn't have wvdc or current ratings. The schematic is from the lid of my K250-2. I made a parts placement diagram, but have no way to determine the diode type. Anyone have any literature on this component?

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Re: K250 diodes [message #6056 is a reply to message #6051]

Fri, 05 August 2005 07:31

stevem
Messages: 4786
Registered: June 2004
Location: NY

Senior Member

If you remove that diode from the board, are any numbers on it?

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Re: K250 diodes [message #6101 is a reply to message #6051]

Mon, 22 August 2005 08:54

Wattsyurz
Messages: 16
Registered: July 2005
Location: SC

Junior Member

The glass diodes are tiny, and barely able to mark the anode, maybe with a microscope I could see numbers!! There are 5 diodes total, these two are to prevent current from backing up on the feed transistors. The 250 power amp board seems very similar to the 200, while the pre amp was redesigned. If nobody knows the rating, I'll have to guess.

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Re: K250 diodes [message #6106 is a reply to message #6101]

Tue, 23 August 2005 11:57

chicagobill
Messages: 2010
Registered: April 2003

Senior Member

Wattsyurz:
I'm not that familiar with the 250 power amp, but Kustom used the same diodes for all of the 200 series amps. The small glass cased diodes in the short protection circuit were Fairchild FD111's. NTE cross references this to a diode rated at 1/4 amp 200v. Personally I've seen the 1N4148 used in the same circuit by Peavey, Crate, Fender, etc., and will probably work here as well.

The bias string diodes are two 1N3193 (axials mounted on the board) and one 1N3754 (mounted on the heat sink with the output transistors). I think that the metal fronts had the same heat sink mounted diode as well.

Bill

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