I use ATC 15 amp fuses to protect my Corsair II. I built up a power
cable with a relay so I can use my shack supply. I looked at the
time-current curves for the Airpax breaker and for these fuses. The 15
amp fuses are used where a 22 amp Airpax would be to speed up the fuse
operation. A fuse is usually rated to carry 125% of nameplate current
indefinitely. I have blown fuses a couple times while tuning a manual
antenna tuner with a brick on the key.
Its best to compare the time-current curves, not just one point on the
curves.
The high speed breakers appear to be still available, though not
necessarily in the same package and mounting as the one originally
specified by Tentec.
73, Jerry, K0CQ
On 1/2/2011 12:05 PM, Bwana Bob wrote:
Well, what prompted this discussion was the fact that I zapped the
finals in my Century 22. It was a series of errors. I had left the drive
set to full power; band was set to 10 MHz, but autotuner was set to 3.5
MHz. I accidentally hit the keyer paddle and let loose 3 or 4 dits,
which was enough to kill the finals. The Ten-Tec 979 power supply did
not trip, probably because a previous owner had used it with a different
radio and had readjusted the over-current trip point. I hadn't bothered
to check it.
While waiting for new finals ( a matched pair from RF Parts Co.) I
readjusted the power supply. I would like to operate the rig on
battery, so I'm looking for a circuit breaker to but in the 13V line,
hence the inquiry to Poco Sales. I have the Airpax spec sheets. The
"instant trip" will trip at 150% of rated load in 100 ms. The fast trip
will trip at 135% of rated load anywhere between 200 ms and about 8
seconds. The slow trip can take as long as a minute to trip.
Older Ten-Tec equipment did not have ALC protection, so they depended on
the power supply or circuit breaker to protect the finals. Ten-Tec
therefore chose the instant trip breakers, which are pretty scarce these
days.
The question is, how fast does a fuse or circuit breaker have to be to
protect the final transistors? It may be better to build an outboard
circuit that duplicates the over-current circuit inside the Ten-Tec
power supplies. I've tripped the power supply for my Corsair many times
without damage.
I will be more careful with the Century 22, as follows: Keep the drive
at zero, unless planning to transmit. Switch from an auto tuner to a
manual one where I can record and physically see the presets for a given
band. Use a fast acting circuit breaker when not using the Ten-Tec
power supply.
73,
Bob WB2VUF
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