Further....

Posted by doodlebug (A) on February 26, 2007 at 07:38:32

In Reply to: Re: Mcintosh 240 dysfunction posted by corerosin on February 25, 2007 at 21:57:16:

I would suspect that there has been a failure of a resistor somewhere in the power supply. Corerosin is on the right track as the high voltage doubler is part of that circuitry.

I've seen this with older tube gear after its been worked on - the failure of some associated components after the amp has been run in a bit. I tend to want to keep someone's amp for about a month for use in regular operation to ensure that there's no drift in spec from the original resistors that are left in the amp.

I've seen these resistors 1) develop cracks which cause noise or arcing, 2) drift out of spec and/or 3) flame out from heating. Lastly, I've also had new, replacement metal-film resistors of the proper wattage fail due to high voltage arcing across the surface of the resistor when used in high voltage circuits. In this case, the fix is to use a larger wattage resistor of the same value in order to increase the spacing between the two ends of the resistor.

I'd suggest you pull the cover and look for part that looks 'heated' in some way. Post some pics, if you'd like, for others to see, too.

As always, know that there's a lot of high voltage in that amp so I do not recommend you attempt to work on it unless you're comfortable you know how to get around in there.

Hope that helps.

Cheers,

David

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Follow Ups Full Thread

Topic - Mcintosh 240 dysfunction - Will Shade 20:34:47 02/25/07 (13)

Re: Mcintosh 240 dysfunction, Michael Samra - gkargreen 15:25:17 02/27/07 (4)

Gkargreeen yes! - Michael Samra 00:13:12 02/28/07 (3)

Re: Gkargreeen yes! - gkargreen 18:20:42 02/28/07 (0)

Re: Gkargreeen yes! - gkargreen 13:09:03 02/28/07 (0)

Re: Gkargreeen yes! - gkargreen 12:23:40 02/28/07 (0)

Re: Mcintosh 240 dysfunction - gkargreen 12:11:05 02/27/07 (0)

Re: Mcintosh 240 dysfunction - Michael Samra 23:28:11 02/26/07 (1)

Re: Mcintosh 240 dysfunction - Will Shade 06:59:35 02/27/07 (0)

Re: Mcintosh 240 dysfunction - corerosin 21:57:16 02/25/07 (4)

Further.... - doodlebug 07:38:32 02/26/07 (3)

That helps a lot. - Will Shade 12:12:17 02/26/07 (2)

Not really,... - doodlebug 12:26:45 02/26/07 (1)

Re: Most Mac 240s have an internal B+ fuse.. - Steve O 13:16:41 02/26/07 (0)

Follow Ups

Further.... - doodlebug 07:38:32 02/26/07 (3)

That helps a lot. - Will Shade 12:12:17 02/26/07 (2)

Not really,... - doodlebug 12:26:45 02/26/07 (1)

Re: Most Mac 240s have an internal B+ fuse.. - Steve O 13:16:41 02/26/07 (0)

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