DIYbanter - View Single Post

rickman

N_Cook wrote on 6/8/2017 4:46 PM:
On 08/06/2017 21:39, wrote:
On Thursday, June 8, 2017 at 1:31:39 PM UTC-4, Cursitor Doom wrote:

If I can source a generic electrolytic of the same spec or better for
30 quid, why should I not use that instead of the bespoke replacement??

Many years ago, my Tek 7603 failed to start. I pulled the power supply
out and was driven nuts by a simple DC voltage regulator problem in the
power supply. A bypass electrolytic capacitor would have been the obvious
solution, except this scope used at least a half dozen extra large Mallory
built capacitors in parallel, and there's no way they all died together.
Adding a bit of external capacitance though brought the voltage right back
and the scope to life. Turns out those big caps were dropping out one by
one over the years and gave no indication of anything going wrong as they
did, until the very last one opened when the supply went out.

Why did I mention all of this? Because I just removed those big Mallorys
and stuck in some standard electrolytics of maybe half the total value and
taking up about a tenth of the physical area of the originals, and the
scope still runs daily with a perfectly clean and stable trace.

In other words, I doubt you'll see any difference by doing what you
instinct tells you. That cap may be very low ESR, have special impedance
specs or ripple current specs, but I'd be stunned if it makes any real
world difference with off the shelf caps. If it were mine, I'd use
Panasonic FR series caps.

When Tektronix had a base in Guernsey, Channel Islands, thay adopted the
following spares procedure.
Each year, divide the stock by half, sell off that half at auction, then
double the price of what they kept in stock.

And this process led to their going out of business sale?

--

Rick C