On Fri, 22 Apr 2016, analogdial wrote:

G Cornelius wrote:

On 04/16/2016 04:00 AM, analogdial wrote:
Tubes last alot longer than paper and electrolytic capacitors.

Now there's a blanket statement if I ever heard one.

My experience with the tube era was that a power supply
would commonly have problems with either the rectifier
tube or the electrolytics.


Series string sets are harder on tubes than transformer sets. Open
heaters and HK shorts are the usual failures. A thermistor used as an
inrush current limiter helps.

The failure rate for paper caps must be close to 100% by now. That
doesn't mean that the circuit no longer works but that the leakage is
now out of spec and they will only get worse in the future. I doubt
there's been a decent paper wrapped elecrolytic seen for at least 20
years.

And the stuff wasn't intended for perpetual use. It was "average stuff"
intended to be used, and then eventually fade away. Indeed, it was
tossed. SSB came along, making a lot of stuff "obsolete", transistors
came along and people wanted that. So in the late sixtes and early
seventies, the old AM and tube equipment was relatively cheap. There was
a period when I was getting stuff, playing with it a bit, then trading it
for something else. Not many were thinking of "collecting", and nostalgia
hadn't set in. So that generally caused the stuff to be relegated to the
garbage, or the top shelf.

It's only in more recent times that the stuff was seen as valuable. So
those capacitors that weren't so great to begin with are now decades
older. The tubes sitting around didn't age (though I finally stripped
some old RCA Carfones, mobile equipment for the trunk of the car, and when
I pulled the tubes, a fair number had been broken, even though I don't
remember them being in a situation for that, they just sat there for
decades), while the capacitors probably kept on aging even when not in
use.

As I said, it's the way they made capacitors up to a certain point,
equipment made after that point didn't use paper capacitors but did use
ceramic, so their life is likely in good shape now.

Michael

Michael Black wrote:


And the stuff wasn't intended for perpetual use. It was "average stuff"
intended to be used, and then eventually fade away. Indeed, it was
tossed. SSB came along, making a lot of stuff "obsolete", transistors
came along and people wanted that. So in the late sixtes and early
seventies, the old AM and tube equipment was relatively cheap. There was
a period when I was getting stuff, playing with it a bit, then trading it
for something else. Not many were thinking of "collecting", and nostalgia
hadn't set in. So that generally caused the stuff to be relegated to the
garbage, or the top shelf.

It's only in more recent times that the stuff was seen as valuable. So
those capacitors that weren't so great to begin with are now decades
older. The tubes sitting around didn't age (though I finally stripped
some old RCA Carfones, mobile equipment for the trunk of the car, and when
I pulled the tubes, a fair number had been broken, even though I don't
remember them being in a situation for that, they just sat there for
decades), while the capacitors probably kept on aging even when not in
use.

As I said, it's the way they made capacitors up to a certain point,
equipment made after that point didn't use paper capacitors but did use
ceramic, so their life is likely in good shape now.

Michael

The caps probably did age even when not in use. I had some old NOS wax
dipped paper caps and they all were leaky. Somewhere in Terman's Radio
Engineer's handbook, he says paper caps can be expected to work as new
for only a few years or so. He had an example for leakage sensitive
circuits in which the usual coupling cap is replaced by two much
larger caps in series with a grounded bleeder in between which,
presumably, would forestall the capacitor aging problem.

Back in the 50s, the higher quality, less disposable electronics, used
those newfangled Sprague Black Beauty capacitors in place of the run
of the mill wax dipped paper caps. I suppose that toxic, short circuit
mess hadn't fully devloped by the mid 60s, when Sprague retained the
name "Black Beauty" for their axial lead mylar film caps. The "Orange
Drop" name for radial lead caps is still around, of course.

Mylar caps replaced paper caps at about time electronics started going
solid state so it's understandable why people associate the unrelibility
problems with tubes.