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In Reply to: RE: External Deemphasis Adjustment posted by David Lawrence on October 31, 2023 at 14:59:06

Neither the MR-71 or the FM-3 have external de-emphasis switchability (as you already know), and the correction can not be accomplished via interconnect. The change to the circuit must be done internally, and with the FM-3 at least, a series of capacitors and resistors must be changed, as shown on the circuit boards above, indicated by the red arrows.

The circuit schematic to change the FM-3 from 75 uS to 50 uS may be available somewhere, but you'd have to know your way around a soldering iron, even if you do find it. I can't speak for the MR-71, which may involve changing a single resistor, but I have my doubts about that.
I think the easiest route would be to do as Itman suggested and find yourself an FM tuner with an external switch, such as his Pioneer F-90 has.
The good news may be that FM tuners are now often available at nearly-give away prices. Visit the Tuner Information Center (link below) and they may have tuners with externally switched de-emphasis listed, to make your search easier.

Tuner Information Center (Open in New Window)

Edits: 11/01/23 11/01/23

Follow Ups:

RE: vintage tuners - ltman 15:52:47 11/01/23 (2)
The challenge is getting one from the Bay that is in excellent condition. Pretty much every seller is going to claim that their unit sounds great and works perfectly.
I purchased an FM3 that was advertised as working perfectly. Nope. (I am doing a restoral)
Then I bought the F90, again, the claim was working perfectly. Yes, for about 20 minutes. After about 20 minutes it starts to generate loud popping noises. (I am doing a restoral)
And I bought a Marantz that was also advertised as working great. LOL this one was obvious, the digital display was frozen. The tuner could be tuned but you never could see from the display which station you had tuned to, or what other settings were in play. (I got a full refund for that).
So be prepared unless you are willing to pay through the nose from a highly skilled restoral expert to have difficulty finding a vintage tuner that works as you would like...
Oh yes, I also bought two Sont -STJ75s. One works great, the other has the common - for that tuner - defect where loud bass passages get muted. I have a plan for that one but no component replacement kit...

Edits: 11/01/23
- True - 1973shovel 04:48:26 11/03/23 (1)
  And today, many otherwise proficient electronic techs won't tackle tuner repair and alignment, since they have neither the equipment or expertise. I fear it's a dying art, but then so is quality FM itself, some might say.
  - RE: True - ltman 23:47:43 11/04/23 (0)
    Yes to both. I am lucky to have an excellent NPR classical station in range:KCNV 89.7
    
    And I am line of sight to their antenna, so doubly lucky.
    
    Many shows are really great and I am learning a lot about classical music. So much so that I started recording the shows to my Sony digital recorder. Probably a "redigitizing" but nothing I can do about that unless I want to record the shows on my Reel To Reels.
    
    I have done the R2R recording in the past, it sounds lovely. But that's a lot of tape, the shows last for 4 hours at least.

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