Mc225 shuts off in stereo

G

Gibbleznbitz

New Member
I recently acquired an mc225 for dirt cheap. Having no experience with mcintosh i set it up and immediately fell in love with the warm sound. However, it only runs with the switch in mono. If i switch it to stereo the amp shuts off. If i put stereo mode on the preamp it only works through the right speaker. If i put it in reverse stereo only the left speaker works. If input it to L+R both speakers work but doesnt sound as full as the sound while in stereo mode (despite only coming from one channel). Any ideas what i can check first as to why this amp shuts off in stereo and only works in mono mode? Thanks in advance!
 
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Gibbleznbitz said:
I recently acquired an mc225 for dirt cheap. Having no experience with mcintosh i set it up and immediately fell in love with the warm sound. However, it only runs with the switch in mono. If i switch it to stereo the amp shuts off. If i put stereo mode on the preamp it only works through the right speaker. If i put it in reverse stereo only the left speaker works. If input it to L+R both speakers work but doesnt sound as full as the sound while in stereo mode (despite only coming from one channel). Any ideas what i can check first as to why this amp shuts off in stereo and only works in mono mode? Thanks in advance!
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I'm wondering if it was dirt cheap that the previous owner knew there was something wrong with it.

Irregardless of McIntosh what is your experience with tube gear in general?

You could check the OEM owners manual, as found in the link below, to see if there is a trouble shooting section

McIntosh MC225 Vacuum Tube Amplifier

www.mcintoshlabs.com www.mcintoshlabs.com

Seeing as you got it dirt cheap I would have an experienced tube technician give it a thorough look over before you possibly do more damage beyond it's current state of operation.
 
What do you mean by "shuts off"?

Sound stops, or literally shuts off e.g. like all the heater filaments go out?
 
Yea i mentioned that it didnt work in stereo but he insisted it did… makes me wonder if he wasnt even aware there was an issue rather than him pawning an issue off to me. Ill take your advice and bring it to a tech nearby that deals with vintage mac gear. Thanks for the quick response appreciate it
 
nothing in the schematic indicates that it should do any such thing. the stereo/mono switch is nowhere near the power, it just bridges the L and R inputs together.

I wonder if someone repurposed it as a power switch. in stock form these do not have one. That honestly seems far more likely than some bonkers fault with that switch that somehow kills the power

as to why it only runs through the right speaker, could be related to whatever was done with the switch, could be something else entirely. A couple pics with the bottom off might reveal an answer.


 
gadget73 said:
nothing in the schematic indicates that it should do any such thing. the stereo/mono switch is nowhere near the power, it just bridges the L and R inputs together.

I wonder if someone repurposed it as a power switch. in stock form these do not have one. That honestly seems far more likely than some bonkers fault with that switch that somehow kills the power

as to why it only runs through the right speaker, could be related to whatever was done with the switch, could be something else entirely. A couple pics with the bottom off might reveal an answer.


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Yea i think you must be right good call. So now im starting to wonder if its a preamp thing with the channels being wonky. Ill connect a different preamp and see what happens.
 
Gibbleznbitz said:
Yea i think you must be right good call. So now im starting to wonder if its a preamp thing with the channels being wonky. Ill connect a different preamp and see what happens.
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I wonder what other changes, if any, were made to this amplifier? The reason I ask is that a Mc225, functioning properly, is not "warm". It is detailed and accurate. Pictures under the hood will tell us a lot.
 
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