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MR-55A tube tuner

that70sguy

that70sguy

Well-Known Member
I recently picked up a Mcintosh tube tuner, the owner identified it as a MR-55A. The tag on the back which designates the model number is gone, but I do know that it is either a MR-55 or a MR-55A.

Does anyone know what the difference is between the two models? I did find an instruction manual for the MR-55a online, but not much info otherwise. I know that the MR-55 was Mcintosh's first tuner.

The unit was dirty, but cleaned up very nicely. All tubes are there, not sure if they are all original. It is missing one knob and one other one is stripped on the inside. The glass is intact and the faceplate is in pretty good condition.

I haven't powered it up yet, but the previous owner told me that it powered up and worked fine.

Anyone have any experience with this tuner?
 
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that70sguy said:
I recently picked up a Mcintosh tube tuner, the owner identified it as a MR-55A. The tag on the back which designates the model number is gone, but I do know that it is either a MR-55 or a MR-55A.

Does anyone know what the difference is between the two models? I did find an instruction manual for the MR-55a online, but not much info otherwise. I know that the MR-55 was Mcintosh's first tuner.

The unit was dirty, but cleaned up very nicely. All tubes are there, not sure if they are all original. It is missing one knob and one other one is stripped on the inside. The glass is intact and the faceplate is in pretty good condition.

I haven't powered it up yet, but the previous owner told me that it powered up and worked fine.

Anyone have any experience with this tuner?
Click to expand...

I have a small collection of Mac tuners including a 55a, a 66 and a 71 among others. I like the 55 primarily for good AM performance. It also looks great next to an early version C20 that I have.

The biggest difference between the 55 and 55a seems to be the chassis layout. The a has a revised and somewhat cleaner layout. Some of the visible differences: non a has meters behind rectangular cutouts. a has meters integrated into the front panel. Non a has antenna input terminals attached above the chassis and 300 ohm twin lead above chassis. Non a has one tube mounted horizontally out the back of the tunner cap assembly.

My impression is that they did some revisions for easier assembly and a cleaner unit in the a. Don't know if there is any performance difference and, if there was, I am sure it would be swamped today by sample to sample condition.

Regards,
David
 
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