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The Consumer Electronics Hall of Fame: McIntosh MR 78 Tuner

sberger said:
I would have no interest in this mod. It would be overkill for a component that gets used to listen to small stations that are not terribly high quality to begin with.
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62caddy said:
Desirability and value definitely higher, usually translating to ~ $500 premium for units so modded from what I observed on the auction site.
I cannot comment on SQ benefits.
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Being an owner of a modded MR78, I must say that there was a noticeable difference in SQ between it and the prior 78 that I replaced it with. I did not compare DX'ing capability, merely local stations in the area. Both units had been totally recapped by Terry DeWick by the time of the comparison. Not that there were any issues with the original unit, on the contrary. I merely stumbled across a Modeferri unit locally at a couldn't pass up price. The modded unit was to my ears, slightly more dynamic, and extremely quiet. Soundstage & imaging were very impressive. While not a night & day difference, it was certainly more than subtle. It's a shame that I don't use it often, there's just not much to listen to locally anymore. The local NPR station does have a couple of programs worth listening to, and the station being local is strong and clear as a bell. The tuner really does a beautiful job. My initial question regarding the modded units was only intended to see what others feel about it.
FWIW, I've owned an MR67, MR77, MR78, and modded MR78. Each one, in my experience performed better that the previous.
 
seacliffe301 said:
The modded unit was to my ears, slightly more dynamic, and extremely quiet. Soundstage & imaging were very impressive. While not a night & day difference, it was certainly more than subtle.
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Sounds similar to the difference I heard between the MR78 and MR80. Not exactly night and day but slightly refined and quieter.
 
seacliffe301 said:
I’d love to be present for a shootout between a Modaferri modded 78 and an MR80.
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I'd like to see that too.


MR78 Signal Strength scale

Searching around for old Mc stuff on the PC.. came up with THREE Signal Strength meter reference points in μV.

Here they are plotted on a LOG scale with a NL (natural log) function fit.

MR78_SS_fit.png


The second chart is with the function regenerated across the WHOLE range using the NL coefficients.

MR78_SS_regen.png


Here's the data table.

You can `massage´ the numbers any way you want in the Plot & List columns (engineers only). :rflmao:
Code: 
Strength   Cal    Regen     Plot     List   (μV)
--------   ---    -----     ----     ----
  10     30,000   30,348   30,000   30,000
   9              10,815   10,500   10,000
   8               3,856    3,800    4,000
   7               1,375    1,375    1,375
   6       500      490      500      500
   5                175      175      175
   4                 62       60       60
   3                 22       22       22
   2                  8        8      7.5
   1                  3        3      2.75
   0        1         1        1        1


One way to make a digital gauge—use the function and coeffs in XML code with the voltage driving the SS meter.

Coefficients
a 1.007723489782
b 1.031279956881


The MR80 has a logarithmic SS scale with LED indicators, which is a BIG improvement over earlier models.


-Greg
 
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One of the things I don't like about my MR 71 is the signal strength meter which almost seems binary - if you have a decent signal it's pegged if you have anything less, it's sits pretty low. Makes it useless for fine tuning. No idea why it works this way or if it can be better calibrated. The meter on my MAC1900 seems better for fine tuning.
 
TSmith8605 said:
One of the things I don't like about my MR 71 is the signal strength meter which almost seems binary - if you have a decent signal it's pegged if you have anything less, it's sits pretty low. Makes it useless for fine tuning. No idea why it works this way or if it can be better calibrated. The meter on my MAC1900 seems better for fine tuning.
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I wonder if that's a calibration issue. I had an MR67 decades ago and I don't seem to remember it operating like that.

EDIT: Never mind. I just looked at a picture of a 67 and realize that I did not have the signal strength meter.
 
TSmith8605 said:
One of the things I don't like about my MR 71 is the signal strength meter which almost seems binary - if you have a decent signal it's pegged if you have anything less, it's sits pretty low. Makes it useless for fine tuning. No idea why it works this way or if it can be better calibrated. The meter on my MAC1900 seems better for fine tuning.
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Contact Mc Support and ask for MR71 data points (low, mid, & high) for meter indication vs. signal in microvolts. Or do a test with an RF generator and power meter, like an HP spectrum analyzer with markers would be GREAT, and plot a table of meter readings vs. RF test signal. Do both and compare the results.

What about the TPs (test points) on the back panel of these tuners? How would the Vert level track RF signal voltage?


-Greg
 
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My wife surprised me with an RF signal generator and HP spectrum analyzer under the Christmas tree because she knew I always wanted one. NOT.

Merry Christmas!
 
Gregory said:
Contact Mc Support and ask for MR71 data points (low, mid, & high) for meter indication vs. signal in microvolts. Or do a test with an RF generator and power meter, like an HP spectrum analyzer with markers would be GREAT, and plot a table of meter readings vs. RF test signal. Do both and compare the results.

What about the TPs (test points) on the back panel of these tuners? How would the Vert level track RF signal voltage?


-Greg
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Back in the 1980s, I worked at a place that designed and built custom stuff, including custom RF equipment. Means we had labs full of certified-as-calibrated RF test equipment. At one point I bought a 1950s National (brand) AM / MW / SW 5-tube radio at the local nerd flea market for $14. One day after work just for fun, our top RF designer put it on the bench hooked to a bunch of HP equipment that likely cost well over $200K and he aligned that little $14 radio. It worked pretty good and I still have it.

Anyway, those days are long gone as is the HP equipment. I am setting up a work bench but not planning to get any RF test gear for it, just audio.

I do have a scope and one of these days I need to plug it into the test point(s) on the MR 71 and see if I can fine tune both frequency and antenna pointing angle. But this radio really needs an alignment and / or I am thinking of replacing it with a newer SS MR XX. Meters on my other, better MR 71 work a little better but are also a bit on-off digital.

Since L&M closed, I'm not sure who can do an MR 71 alignment in the SF Bay Area. I was recently at a local shop full of interesting used / vintage gear which also had a service bench in the back. I even saw an MR 71 sitting on the pile. I asked the (sales, not service) guy if they could align my MR 71 and he did not even know what I meant. !!
 
Late to the topic, may able to get a nice MR 78 early version, meaning no output filters.
Thinking about installing a MPX board and buffer board, am I crazy for doing it ?
 
Yes here
"there are at least two different versions of the MR 78 with different audio stages. The early MR 78s have no low-pass filtering before the outputs, while the later models add a pair of 'brick wall' three-inductor 15 kHz LPFs and a pair of buffer amplifiers."

The early version not that good
 
PabloTincho said:
Yes here
"there are at least two different versions of the MR 78 with different audio stages. The early MR 78s have no low-pass filtering before the outputs, while the later models add a pair of 'brick wall' three-inductor 15 kHz LPFs and a pair of buffer amplifiers."

The early version not that good
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Did not know that, glad mine is one of the later builds, plus it's a Modeferri modded unit. I wonder he he corrected that on the early builds that he modded.
 
The MPX in the MR-78 is garbage, and that is coming from David Rich, in addition James Bongiorno stated "
McIntosh MR78 could also be squeaked in although the audio sections leave much to be desired."
 
Garbage may be a tad harsh. I've owned several of Bongiorno's designs - only the Thalia remains. To each their own.
 
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