[TenTec] Ten-Tec PA design

[James C. Owen, III]

Hi Bill,
   A few thoughts on this. A fuse has never been included in any
device to protect the device itself but to protect the system
(wiring) before the device. Suppose you didn't have a fuse at the
device and had a short. If the main fuse was a say 20A and the
wiring was good for 10A then likely the wiring would burn and
maybe burn the house down. However a breaker is a fast acting
magnetic device that will protect the device as well as the
system. The question of why TT didn't included a breaker instead
of a fuse--well in a way they did--it's in their matching power
supply. This is an electronic breaker not a magnetic and it works
as good if not better than the magnetic. The fuse in the rig is
then just a backup to protect the wiring system in case the
breaker should fail and to protect same if someone uses other
than a TT power supply. TT has always recommended to use an
Air-Pax breaker if their power supply was not used and if sized
correctly it works fine. I have a  20A fast Airpax in the line
with my Jupiter since I use a 35A Astron PS. I occasionally trip
the breaker, usually because I select the wrong antenna and have
never blown a fuse. In fact I once used a 22A breaker and it
wouldn't trip on these types of overloads. I once saw 27A on the
Astron meter. I would not go over 20A for the breaker.These
breakers will not trip until you exceed about 135% or rating. TT
use to suggest using a 18A instant trip but these are very hard
to get.
   Hope my thoughts have generated more thoughts on Airpax
breakers.

73 Jim K4CGY

--- Bill Tippett <btippett at alum.mit.edu> wrote:

> K5KVH wrote:
>  >Add a circuit breaker per the Ten Tec
> supply practice, and you should be fine.
> 
>          I hesitate to bring up the Air-Pax
> debate again, but can anyone explain why
> TT does not use the Air-Pax instead of
> a normal 25A fuse.  Surely not cost in a
> $4k rig like Orion.  I don't mind adding
> an Air-Pax but it causes me to wonder why
> TT did not design it in to begin with?
> 
>                                  73,  Bill  W4ZV
> 
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