I built 25 350W VHF paging stations. They all used solid state amps and
we finally settled on Duracomm DPS75 power supplies. The switching power
supplies were much more reliable than analog supplies and much easier to
schlep into walk-in remote sites. I never, ever used a fuse holder,
depending instead on the current limiting of the supply. In almost 20
years I never, ever had any problem due to over-current. However when
using batteries, you absolutely have to have a fuse.
With high-current systems you have to eliminate every voltage drop you
can. All the transmitters I built had 350 amp quick-disconnects on the
PAs for fast, east changeouts of failed units. Paging has a lot of
thermal stress and the PAs created maintenance issues. I learned a lot
about fixing MICOR 100W PAs maintaining IMTS systems. In these
situations I tend to think that the old conduction cooled tube PAs were
better. Of course, high voltage power supplies are another animal but
are (were) much more reliable.
Ah, the old days. Thanks for reading.
-de John NI0K
Jim wrote on 6/2/2020 8:17 PM:
Oh... And I don't use fuse holders between my Icom or Kenwood HF rigs
and the power supply either. I use Astron switching power supplies
(SS30 or SS50) and or an RS50A
Thanks
73
Jim W7RY
On 6/2/2020 8:05 PM, Artek Manuals wrote:
I dont recall at the moment ...what is your point?
On 6/2/2020 9:04 PM, Jim wrote:
How about during normal operation? What power supply?
Thanks
73
Jim W7RY
On 6/2/2020 7:48 PM, Artek Manuals wrote:
During the Bench testing I have an Astron R-35 more than up to the
brick's challenge of 10-15 amps and fairly short power cable less
than 18"
Dave
NR1DX
On 6/2/2020 8:38 PM, Jim wrote:
What are you using for a power supply to run this amplifier?
Thanks
73
Jim W7RY
On 6/2/2020 7:33 PM, Artek Manuals wrote:
This is going to seen trivial to many of you but some times the
most puzzling problem has the most simple solution, worth sharing.
The " 60W-brick" ( an old Mirage C106) on the 220 "lets chase
DX"-repeater had given up the ghost. No power on light ...hmmm
checked and the fuse on the back panel fuse holder� looks
absolutely perfect. So out of the rack and back to the home shop
for a more detailed autopsy. After 5 minutes of poking around
with the VOM it seems the fuse is actually a zombie fuse, meaning
it looks OK but in reality it is open with no sign life or the
cause of death, usually 15 Amp fuses die pretty spectactularly.
Oh well pop in a new fuse and it is off to the races. But the amp
is only putting out 40-45 W and it is supposed to be 60W? Playing
for 10 more minutes and nothing seems out of the ordinary..oh
well it is 30 years old anyway button it up and move on to the
next project right? As I put the cover back on I happen to absent
mindedly tighten the fuse holder cap and it is VERY WARM ...now
wait a minute fuse holders aren't supposed to be that warm?
Further measurement shows� a little better than .5 volt drop
across the fuse holder under load. A little loosen-tighten cycles
and it is down to .25 volts . Upon closer inspection the spring
inside the fuse holder looks dark and crusty ( like the one in
your flash light after the batteries leak). So I have some really
nice fuse holders in the junk box with bright shiny copper
insides , replace the fuse holder , no more voltage drop and the
brick is at 70W out.
The moral is the old fuse holder was corroded internally to the
point that it's contact resistance had gone up enough under load
to heat the fuse contact end and melt the solder inside the fuse.
The bigger take away is that if something seems a bit odd keep
looking. This one was easy but in 50 years of tinkering I had
never seen a bad fuse holder and now I wonder how many I over
looked over the years 8^)
Dave
NR1DX
manuals@artekmanuals.com
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