Electronics > Projects, Designs, and Technical Stuff
My Dad's Vintage Hi-Fi Fisher Amplifier KX-100 / KX60 Tuner
joeqsmith:
I had saved my dad's old Hi-Fi. Sure it has sat around ever since. Noticed my wife had decided to move the box to the garage, which is just one step closer to the dumpster. So I brought it back into my lab where it is safe for now. The amplifier is a Fisher KX-100.
I remember going with my dad to buy it. I've spent countless hours listening to it. Like my wife's grandmothers old radio that her mom remembers listening to as a child, I just didn't have the heart to let it go to the dump.
The amplifier has not been powered for several decades, so first things first, check to see if it has any damage. First thing I noticed was one of the finals appears to have started to leak. I remember being around 11 or so YR and one of the tubes failed. I had my mom take me to the local store (tubes were common then and they even had testers for customers to use). It turns out, this is the tube that appears to be failing. Note the others are still marked with Fisher.
Opening the chassis up (zero concern about any sort of shock, as 30 years of sitting, everything should have discharged. lol). Started going through all the caps and sure enough, one was shorted. Outside of that, none of the smaller caps appear bad.
I then started to reform all the electrolytics. Nothing appears to have a high leakage. I'll let her sit and cook.
The case is made from cheap plywood. Similar to how I have made cases for some of my home projects. The wood had split where the grill slides in and it had a couple of deep scratches I wanted to smooth out. After repairs, mixed up some stain to match the original colors. I have no plans to use poly on it like I have with some of my projects. Thinking just some oil and I'll call it good.
Maybe tomorrow I can turn on the chassis, less tubes, assuming all the caps check out after reforming.
rsjsouza:
Joe, great job keeping this relic out of the dumpster, especially with such sentimental value attached to it. I don't see any wax bombs, fortunately.
I have my grandpa's Philips radio restored and it is a family heirloom.
Have fun!
TimFox:
The cap in your first photo:
Capacitors of that type and vintage often absorb moisture.
I replaced each of the range caps in my Tektronix L,C meter, and they all tested bad out of circuit.
I would replace each such cap with a modern polypropylene unit.
floobydust:
It looks like a fine amplifier.
I would advise caution, I've never seen those electrolytics (cans and orange Cornell-Dubilier) at that age that has not failed. They don't have safety vents either.
As long as the output tubes have proper bias, or else they will roast. I can't tell if the design is self-bias or not here, then the cathode cap is critical.
joeqsmith:
Typically I won't shotgun and most likely I will leave everything alone, only addressing the problems I identify. The small 150V 100uF orange, below 0.03*100*150 or about 450uA it's fine.
https://www.mouser.com/datasheet/2/231/161587867495-2585920.pdf
At 159V (over the rating) it's around 220uA. At 130V, its below 60uA. BK RLC meter, ESR measures 0.65. Capacitance also checks good.
The 200uF 250V cap measured about 40uA at 260V. ESR was under 1.5 ohms. Capacitance was a bit low but nothing of concern. The other 200uF was also alright but it's shared 40uF section isn't looking so good. During the cycle, the leakage was about double what it should have been below the spec'ed voltage, I cranked up the current to about 1.5mA. It made it to about 470V and broke down. No idea yet about that last can.
I couldn't let the finish go and put a light coat of poly on. Well maybe one more tomorrow. lol. Scratches came out fine. Guessing those came from us kids.
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