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Re: [TenTec] Airpax Breaker Part and Source

To: tentec@contesting.com
Subject: Re: [TenTec] Airpax Breaker Part and Source
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Reply-to: geraldj@weather.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 02 Jan 2011 12:29:16 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
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 

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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