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McIntosh MR 74 Tuner

H

Ham’r

New Member
I have a McIntosh MR74 Tuner, a C33 Preamplifier and an MC2255 Power Amplifier. I recently noticed that the MR 74 is sounding "wonky" below (approximately) 96 MHz (or so), I cannot seem to lock a good signal, signal lock or clean audio. Above 96MHz, the signal and audio clean up. It sounds like I have a weak filter capacitor. Does anybody (a) know of a good vintage McIntosh mechanic in the Southern New Jersey (the Western Atlantic County) area, or (b) have any idea what the issue may be?

Thank you for your insight.
 
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There's also a guy in northern New Jersey, Tim Schwartz of Bristol Electronics who is/was recommended by fmtunerinfo.com. I have not used his services, so I'd contact him to discuss, if I were you. Here's info from a google search.
5 Riverview Ln, Ho-Ho-Kus, NJ 07423
(201) 447-4299
 
It's almost certainly NOT a filter capacitor if it works fine on the upper half of the band and not the lower. Bad filter capacitors would cause hum everywhere.

Not sure what amounts to "wonky" but it could be IBOC interference. Lots of discussion threads on that here on AK.
 
Ham’r said:
I have a McIntosh MR74 Tuner, a C33 Preamplifier and an MC2255 Power Amplifier. I recently noticed that the MR 74 is sounding "wonky" below (approximately) 96 MHz (or so), I cannot seem to lock a good signal, signal lock or clean audio. Above 96MHz, the signal and audio clean up. It sounds like I have a weak filter capacitor. Does anybody (a) know of a good vintage McIntosh mechanic in the Southern New Jersey (the Western Atlantic County) area, or (b) have any idea what the issue may be?

Thank you for your insight.
Click to expand...
Define "wonky" please.
 
I have the same trio and had the tuner gone over by a tech who worked at McIntosh starting in the 60s. It functions fine as far as I can tell, but it is pretty much useless due to the geographic barriers between me and the transmitters. The south part of the Boulder valley is notorious.

I'm not an expert in FM, but I'm wondering if the real issue in the difference between the ends of the dial is different wavelengths.
 
w3jn said:
It's almost certainly NOT a filter capacitor if it works fine on the upper half of the band and not the lower. Bad filter capacitors would cause hum everywhere.

Not sure what amounts to "wonky" but it could be IBOC interference. Lots of discussion threads on that here on AK.
Click to expand...
It is almost like a wall and as the VFO is turned, the signal goes up, and there is a squeal, but no discernable audio. That does not happen at the upper end of the VFO.
 
edwinh said:
I have the same trio and had the tuner gone over by a tech who worked at McIntosh starting in the 60s. It functions fine as far as I can tell, but it is pretty much useless due to the geographic barriers between me and the transmitters. The south part of the Boulder valley is notorious.

I'm not an expert in FM, but I'm wondering if the real issue in the difference between the ends of the dial is different wavelengths.
Click to expand...
I thought the same. I live in southern new jersey, halfway between Philadelphia (30 miles to my west) and Atlantic City (30 miles to my east). The lower side of the FM spectrum 94.5MHz has several stations in the Atlantic City area that have a relatively strong signal. As I run the VFO up to about 104MHz, everything cleans up around 100MHz . I attempted to reproduce but was unable to with with my shop receiver, a Kenwood KR-5340 receiver, my Marantz Model 4400 (a beast), and my Marantz 2270 (a gold standard). I did not hear any of MR 74 distortion and was able to lock in the FM Stations using the exact same antenna configuration with the 3 other receivers.
 
Maybe your LO misbehaves at lower frequencies. I've had that in a Pioneer from the seventies. It is hard to fix without specialist equipment, notably a spectrum analyzer. The Pioneer's LO had issues with an inductor in the mixer. Very weird fault. I expect something similar in your Mac.
 
PE9ZZ said:
Maybe your LO misbehaves at lower frequencies. I've had that in a Pioneer from the seventies. It is hard to fix without specialist equipment, notably a spectrum analyzer. The Pioneer's LO had issues with an inductor in the mixer. Very weird fault. I expect something similar in your Mac.
Click to expand...
Thank you for the advice. It is very much appreciated. I am an amateur radio operator and I am sure members of my radio club have the knowledge and technology to check it out.
 
Sorry I got nothing but an inspiration to fix it. I've found all the good stations are on the left side of the dial...
 
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