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I am upgrading a Sansui TU-9900 tuner. The rectifier curcuit is currently four out of date diodes (1S1850). The specs are:VRRM 200
I(RM) max 10U @ 200
I(FSM) 50 @ 10m
V(FM) max 900m
I(FM) 750m @25C
I(O) max 1.5 @60CI want to upgrade to the best quality possible for sound. I'm also upgrading with quality Caps BTW.
What would I use? What parameters do I need to match or exceed? What are the key parameters you look at in replacing a diode? Do I use Shottky or Hexfred or ??
I know some of this is basic but I'd appreciate a little education.
Thanks, Denny
Follow Ups:
are fast soft recovery diodes that would work well. The 11DQ10 schottky is only rated to 100V, 1A whereas the UF5403 is rated at 300V 3A and exceed all the specs of the 1S1850. They have about the same forward voltage drop (1v) so they should give about the same output voltage as the 1S1850's. These are low cost at Mouser.
The best source for information regarding FM tuners is here: http://www.fmtunerinfo.com/ You'll find specific information about your tuner and general information regarding tuner mods.My experience shows that replacing your stock rectifier diodes with Schottky's will reward you with a much cleaner sound. And that's just the beginning of what can be done.
Good luck with your Sansui, which is an excellent tuner.
Bob
Thanks. I have gone to fmtunereinfo and they don't have specifics for thr TU-9900.I still have the question of how do I decide which shottkys to get. Which parameters or specs of the old one to I have to duplicate or exceed or not exceed?
I'm no electronic engineer, so I can't give you the exact way to determine what you need, but I've read that the voltage rating for Schottky's needs to be higher than for the original silicon diodes. In the tuners I've modified, I've used 85 volt/3 amp Schottky's that I picked up at my local electronics supply store, and I've used some 100 volt/5 amp ones that I got through DigiKey. I've also used the 5 amp Schottky's in vintage receivers with no problems, so you'd be totally safe with them in your tuner which doesn't draw nearly as much power.Again, I'm no expert, but I don't think the actual value you install makes a lot of difference (at least to the sound) as long as you get to, or beyond, that minimum value.
Maybe I've just been lucky, but I've installed Schottky's in almost all the solid state stuff I have using the above guide lines, and the results have always been good.
Schottky are the best if you can find them in the voltage/amp rating you need, they are harder to find in high voltage/amperage ratings. Hexfreds are next best and are more widely available in higher voltage/amp ratings. Ive used the IR 11DQ10 100v/1.1a in my Marantz cd63se uppgrades and they worked well.
If you have the real estate and the bucks, diodes can be paralleled for greater current and seriesed (ok, you make up a word for that) for greater voltage.
You're right about that. I've wanted to install Schottky's in my tube equipment but have found them very hard to find. Parts Connexion has some, but they're beyond my budget.
Only need to install ONE diode to get all the alleged benefits from the new and improved design. But then the Vendors don't tell you that, either from ignorance or greed... you decide which :-)
regardless of diode selection. I'd concentrate on the caps and
elsewhere if I were you.Good luck.
Several years ago I spent a year or so tweaking an old nearly dead NAD 7020 reciever. I replaced most of the electrolytics in the amp and preamp sections, mostly with Nichicon Muse and a few Black Gates. That was a nice improvement. But when I replaced the power supply bridge diodes (there were two rectifiers, one for the main unregulated supply and a second for the regulated supply) with FRED soft recovery diodes there was a major decrease in grit and grunge... things smoothed out to an incredible degree. IME, in this case the diodes had a larger sonic impact than the new caps.
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