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Hi everyone,
not sure where this should be posted since I think CD players have fallen far out of favor, but I figure this is where I'll find the most expertise ;-).
I have an old AH! Tjoeb 99 CD player based on a Marantz CD-38 with a tube output stage. A few months ago it started making a nasty ground hum, and I've used my oscilloscope to trace it back to the power supply of the add-on output amp, specifically a fairly symmetrical triangle wave on pins 2 and 8 of each 6922 (respectively, the grid of each tube's first triode and the cathode of its second triode).
I can see no visibly failing filter caps (they are Elnas, which I understand are quality units), and probing under the board is pretty difficult because all the signal and transformer leads are really short, so I'm wondering if anyone has an idea of how to figure out which parts are failing.
There are 4 transistors in the power supply section. My understanding of circuits is pretty basic and doesn't include the function of transistors in linear power supplies. Are these likely culprits, or is it more likely a diode? Or should I just replace all the filter caps and call it a day?
Thanks
Dan
Follow Ups:
Yo Dan,the rating is 1000 hours at 85C in application and doubles for every 10C cooler so let's see how long they will last at 35C, 95F since some like it hot. 75C=2000hrs,65C=4000 hours,55C=8000 hours,45C=16,000 hours,35C=32,000 hours. 25C=77F=64,000 hours. I'll take 32.000 to 64,000 hours with the Silmic before hundreds of thousands of hours with inferior sounding caps any lifetime. Just change them every 64,000 hours, or a bit before just to be safe.
It's a New Dawn It's a New Day It's a New Life-- And I'm Feelin' Good -- Leslie Bricusse
Edits: 02/02/21
I would start with the larger electrolytics and see what happens. The waveform you describe could indicate that the filter caps could be either high ESR and/or low capacitance due to dielectric changes. Might not do it but not an expensive experiment.
Mike
Thanks Mike,
I did some more digging with my oscilloscope and figured out which caps are on the bad rail. Desoldering one of them revealed a small leak which was hidden under the cap. So I'm going to do as you say, and just replace all of them.
Dan
I suggest you give some thought to what caps to use, like good sounding ones made for audio.
It's a New Dawn It's a New Day It's a New Life-- And I'm Feelin' Good -- Leslie Bricusse
Do you have recommendations? I found the same ones I took out (Elna 1000uf at 35v)...
I'm not disagreeing with the suggestion but I usually try to find high temperature alternatives because they last longer. Still also focus on important specs like ESR.
Just FYI
Mike
I'll stick with known great sounding caps made with audio in mind. There will last a very long time at room temperature.
It's a New Dawn It's a New Day It's a New Life-- And I'm Feelin' Good -- Leslie Bricusse
I have no idea if the Elna caps would sound better in a psup circuit vs. another electrolytic cap with good specs but, in this case, it does seem very likely that the Elna caps have failed in a "room temperature" application.
Mike
I myself love the Elna Silmic II. IMO they are pretty accurate but many may thing they are too warm. Nice full sounding , Then there is the Nichicon Muse, KZ is the highest grade, I think. Digi-key has Silmic II 1000@35v in stock. You can get free shipping with them if you call and arrange a prepayment. The KZ comes in a 50v. If you want good to very good go with the KZ. If you want dogs gift to the discerning audiophile with great taste go with the fabulous Elna Silmic II. This is what juaneda has to say about the Elna's in his cap review."Elna Silmic II is the best device of this test. Comparing with very good Black Gate, Elna sounds better. There is as difference between Sprage and Black Gate than Black Gate and Elna. It is certainly the best choice on electrolytic capacitors for top end devices. Good sound for classical, baroc, jazz and modern music." EDIT: I forgot to mention that the Elna Silmic IIs are reported to be Nelson Pass's favorites.
It's a New Dawn It's a New Day It's a New Life-- And I'm Feelin' Good -- Leslie Bricusse
Edits: 02/02/21 02/02/21
The caps did the trick!
I bought the Elnas (same caps it had), may in the future try the fancy caps.
Thanks for your help :-)
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