Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!hao!ames!sdcsvax!brian
From: brian@sdcsvax.UCSD.EDU (Brian Kantor)
Newsgroups: rec.audio,sci.electronics
Subject: I really ***HATE*** electrolytic capacitors
Message-ID: <3646@sdcsvax.UCSD.EDU>
Date: Tue, 11-Aug-87 06:58:09 EDT
Article-I.D.: sdcsvax.3646
Posted: Tue Aug 11 06:58:09 1987
Date-Received: Thu, 13-Aug-87 00:38:46 EDT
Distribution: na
Organization: UCSD wombat breeding society
Lines: 66
Xref: mnetor rec.audio:2768 sci.electronics:1144

I'm sitting here at my workbench surrounded by a pile of bad
electrolytic capacitors that I just got through ripping out of my
stereo.  Here's the story.

I've been noticing a gradual deterioration in the sound quality of my
stereo for some time, but I'd thought it was my ears, age, lack of hair,
too many earrings, excessive exposure to punk, cat fur, etc.

The other day, however, I played a CD for a friend, and we looked at
each other and agreed that it really sounded bad.  That whirring sound
was Bach spinning in his grave at the distortion.  Ok, add "fixing the 
stereo" to the list of things that need to be done.

Got to it last Sunday.  First, let's take the power amplifier, a Dynaco
ST80.  Not a bad amp back in 1973 when I bought it.  Hmm. DC voltages
are fine.  Let's measure the response and distortion.  Fine too.
Nothing wrong here - they're just the same as when I measured them after
I put it together.  Channels match, too.  Bridge the power supply caps
with some .1uFs anyway, to bypass the internal inductance of the large
filter caps.

Preamp - a Dyna PAT-4.  Also pretty good for 1973.  Check some DC.
Voltages ok, but there's some ripple on the power supply.  Ok, well the
filter capacitor is a three-section electrolytic, so bridge some test
capacitance across it, and see what happens.  Hum gets worse.  Damn,
there is inter-section leakage.  Rip the thing out and replace it with
three separate electrolytics.  Might as well bridge them with .1 caps
while I'm at it, cut down the high-frequency power supply impedance.

Hmm. Better check the other capacitors.  Dig out the old capacitance
bridge (yes, it has a magic-eye tube in it!).  Well, all the 50uF
coupling capacitors are too leaky to measure what value they still are,
and the 5uF ones are about 1uF, and the 100uF bypasses are about 25uF,
and the 330uFs are shorted.  Sigh.  I didn't even test the rest of the
capacitors.  I replaced EVERY electrolytic capacitor in the preamp -
about 4 hours work, and $10 worth of parts.  I used tantalum
electrolytics where I could get them - at the local surplus store, the
tantalums are about 10cents more than the aluminum ones, and they're
reputed to have less internal inductance, so why not?

Next, check the tuner - a Dyna FM-5.  Pilot lights are burned out, change 
them.  Now the hum comes up, ok, the filter caps in the supply have dried 
out, and the increased load of running the pilot lamps killed the supply, 
so change them too - another multisection.  Replaced it with separate caps
too, just to be safe, and bridged them with .1uFs also.  Now, how about
the bypasses in the audio stage.  Yup, they're dying too, so change all
of them and the coupling capacitors too.  $3 worth of capacitors, sigh.

Put the system back together, and it sure sounds a lot better, but the
bass still isn't as solid as I remember it being on the 1812 cannons....

Oops, I forgot the Bose speaker equalizer.  Yup, all the electrolytics
in here are bad too.  Back to the surplus store for another $3 worth of
capacitors, and another 2 hours to change them all.

For a 15-year-old stereo, it sure sounds good again, and the cannons 
still scare the cat, and my hair is growing back, and the sun just
started to come up, and I'm going to bed now.  Next year I buy a new 
stereo.

I >>> HATE <<< electrolytic capacitors.

	Brian Kantor	UC San Diego

   "There is more harmony in films than in life."
	- Francois Truffaut