|
Tubes Asylum Questions about tubes and gear that glows. FAQ |
|
|
|
Tubes Asylum Questions about tubes and gear that glows. FAQ |
|
In Reply to: Steve Oda: More mc275 re questions posted by Jareb on August 26, 2002 at 08:30:45:
Jareb,Sorry to hear about your continuing problem. It sounds like one tube is doing all the work which is how the output section of a Mac works. If your speaker is the issue just switch it to the other channel and we will know. Most techs will test the amp on load resistors with a scope and generator. I do not believe your speaker is the problem but this test is one way to eliminate that.
Not all of the parts are on the board you bought. What is left is some wiring from the tube sockets through a connector which plugs on the main board. I would inspect these closely.
The remaining parts are the two,220 ohm, 5 watt sand blocks, and the
2.2uH chokes. If you have not replaced the sand blocks I would change them first as we have had some issues with these and they are cheap, less than $.50 a pair. The sand blocks are designed to fail when a tube shorts and one of yours may have been wounded in a past tube failier.The 2.2 uH chokes are available from the McIntosh parts dept. under #12017.
Do you have a service manual? If not send me an email with your fax number and I will send the voltage charts and a schematic so your tech will know what to check. If you run the amp up to 50 watts at 1khz, you should be able to spot the imbalance on the AC measurments.
On the output tubes,the resistance of pin 3 should be 19.5 ohms and pin 4, 238 ohms (19.5 ohms + 220 ohm sandblock) with the amp off and C18A shorted to ground. Caution! C18A is a power supply cap and needs to be blead off before grounded! This measurement should cover the output trans primary and the two parts mentioned above.
If the issue is the output windings of the transformer, both tubes would be weak.
Ron-C
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Re: Steve Oda: More mc275 re questions - Ron-C 08/26/0216:26:04 08/26/02 (2)
- Re: Steve Oda: More mc275 re questions - Jareb 06:53:48 08/27/02 (1)
- Re: Steve Oda: More mc275 re questions - Ron-C 17:54:24 08/27/02 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
