Here, where I'm working we sold about 10000 computer+monitors
pairs plus other thousands of other monitors sold separately.
We had to provide warranty for about 2000 of them, the rest
being warranted by our suppliers.
Over 90% of them have filtering capacitors 220uF/400V 85C
Taiwan/China made. Inside PS temp is over 60C in the summer.
>From the first day I ordered 30 spare filtering caps.
>From 5 years I serviced over 500 monitors and found
not even one of these filtering capacitor to go defective.
Now some of these capacitors are inside my 2x4-400 linear...
I saw many home made amplifiers pictured on the web, also
commercial ones at the hamfest and I'm used to see very big
ceramics switches, doorknobs, vacuum variables and 8 mm
diameter copper tubes coils, many kilo's of PS filtering and
very, very big blowers.
I have to say that when I first saw the Harris RF-110A inside (1 kW
out 4:1 SWR as the manual says), I was disappointed.
2250 volt B+ (variations admitted up to +10%), with only 2500V anode
coupling cap rating, and also a cooling fan (high speed axial one!) and
no B+ filtering cap (use 3 phase PS).
I saw also part from some commercial (non amateur use) linears
used for RTTY only, for many hours almost on every day, and this
for many years.
The two QB5/1750 sockets and some related components were
mounted on a PCB directly (but with a good PCB layout!), no heavy
thick wires there, but a lot of spare tubes were still on stock, because
was no need to use them.
It is easier for us to build them for 1kW using 10kW rated
(and more expensive) components than to use good and efficient
engineering (like the use of a fan cooling for the output tank
components for example).
I also used the "heavy way" for many time (including big caps)...
I almost broke my back when tI ried to move my first 13.8 volt
20 amps PS! Now I change my operating QTH and have to
found another good solid table for my shack...
73s,
Traian
Steve Thompson wrote:
>
>
> This got me thinking, and I wonder if we are overly pessimistic about
> electrolytics, maybe based on the poor quality components of the past.
>
> Based on a 3kV supply with a stack of 10 x 330u 450V ordinary (not special
> computer grade) 85C caps, rms ripple current rating is 1.5-2A (depending on
> brand) with dissipation about 2W at maximum ripple. 2W doesn't seem a huge
> amount for the size of can to dissipate.
>
> Roughly, rms ripple is around 2xdc for a bridge, and 2.5xdc for a doubler,
> so these caps would be inside rating for, say, 7-800mA dc in a typical psu.
>
> The Siemens version I looked at quotes 10,000 hours life at full ripple at
> 85C ambient. If we work on 65C ambient, 50% tx duty and 50% loading for
> ssb/cw use, then the lifetime prediction is 160,000 hours (18 years)
> continuous operation.
>
> Steve
>
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