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MCINTOSH MR78 FM TUNER

B

BobOnTheJob

The manual on the MCINTOSH MR78 claims it will take 12 volts of RF input...has anyone ever witnesses overload or intermod on an MR 78?
 
I read that too. It's a great tuner. I would tend to believe that spec. I tried it for several months, and the guy I borrowed it from also found an MR-80 that I tried. The first adjacent selectivity is fantastic on both. I actually think I preferred the MR-78. The MR-80 seemed to drift when not AFC locked, and locked back on to the stronger signal on a fade of the weak signal when in the locked AFC position. When IBOC signed on, the regular first adjacents were wiped out, and it was frustrating to have such a good tuner reduced to the level of much cheaper ones by the IBOC sidebands. Now you almost need a phased interferometer antenna to get back to the previous numbers of regulars and DX.

I witnessed no RITOIE on either, but I have never lived in an area of super strong signals.
 
BobOnTheJob said:
The manual on the MCINTOSH MR78 claims it will take 12 volts of RF input...has anyone ever witnesses overload or intermod on an MR 78?
Click to expand...

Is that just a "survival" spec, or does it mean that it will meet all its performance specs with an r-f input of 12 volts. And what if that 12V value is not on a frequency you want to use?

I have a McIntosh MR-73 that I bought in 1966 (to replace an MR-55A), and still have the MR-73 working in my LR stereo setup. The AM section in it died, but it wasn't very good in the first place -- nothing like the AM performance of the MR-55A, which had 3 choices of IF bandwidth. The widest BW gave a 9.5 kHz upper limit to the demodulated audio, and had a 70 dB "whistle filter" notch at 10 kHz to suppress the hets caused by the carriers on adjacent channels.

I just looked at the IB for the MR-73, and it doesn't state what the max r-f input voltage can be.
 
If you had an MR-78 or MR-80, who would you recommend to service them to repair or get them back to specifications? I know McIntosh recommends that they do all servicing. Just shipping would cost a fortune. Those units are quite heavy.
 
The brass ring of MR-78 repairs/updates is for Richard Modafferi (the gentleman who designed the MR78) to do the repairs and his list of updates which will bring the already amazing MR78 to a point that exceeds it's original factory specs. It's salty...$700 plus shipping but for the serious collector, it's the way to go.

http://audioclassics.com/mods.php3
 
Thanks, Bob. Does he have anything to cancel the IBOC sidebands on the first adjacents?

The 12 V test specified 12 V at 104.3 and the response at 96.3 or vice versa. I can't recall if that was RMS, Peak To Peak, or what. I assume it was RMS.
 
Schroedingers Cat said:
Thanks, Bob. Does he have anything to cancel the IBOC sidebands on the first adjacents?
Click to expand...
Well, kind of. The IBOC sidebands "only" occupy 1/2 of the adjacent channel. If there's only IBOC on one side of the frequency you're interested in, it's possible to tune on the 'far' side of the IBOC mess in the narrow band position & often pull out the desired signal. If there's an IBOC on 103.3 and 103.7 (like there is here), 103.5 is toast no matter what.

My 'new' MR78 just arrived this week (it has the modifications I spoke of). There's a 5KW FM on my tower. The FM yagi is 110' directly below the FM 4 bay. The MR78 did intermod until I put an old passive tunable FM notch filter in line (the S meter on the MR78 is amazing--it allowed me to tune the notch filter & get the local FM station down to an 8 on the meter!). With the MR78 in the narrowest mode, I can hear a 6KW on the lower adjacent and a 50KW on the upper adjacent (each about 80 miles out) with only the smallest amount of slop from the on-site FM station. Amazing tuner...
 
Schroedingers Cat said:
What's the charge for the MR-80? The same? And does that include any repairs?
Click to expand...
I believe the $700 includes modification parts...there may be an extra cost for repairs. IIRC, the link said that the $700 covers "tuners" so I'd expect the 78 and 80 to be equal in the cost dept.
 
OKCRadioGuy said:
After the mods, how would it compare to a good DSP radio like the Sony HD tuner or the BW Broadcast rebroadcast tuner?
Click to expand...
Can't say as I've never had my grubby paws on either of those tuners. If they are based on the same DSP chip as the Tecsun portables or the Pioneer SupertunerIIID, one could expect them to be very good...as long as you were at least several miles from the nearest 50KW FM. Those units don't 'overload' or 'intermod' but when they are near a strong FM signal, their sensitivity is reduced by a substantial amount.
 
The Sony is fairly imune to frontend overload as long as it's not right on the same tower, etc. I haven't had the chance to try the BW tuner yet in the RF hell of our tower farm. They claim that it's pretty imune. At some point soon we shall see...
 
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