[TenTec] Airpax Breaker Part and Source

[Bwana Bob]

Jerry:

Thanks.  I have the original breaker that Ten-Tec used on the Corsair 
and it translates to an Airpax "instant trip", which are scarce. The 
fast trip appears to be an acceptable substitute, though.  I'll look 
into the specs on the ATC fuses. A 5 amp fuse might be a good choice for 
my Century 22, instead of a breaker.  ATC fuses are certainly cheap and 
plentiful.  Good idea on the relay, too.  My Corsair on/off switch 
controlled the AC input to the power supply, but it still eventually 
burned up.  I haven't gotten around to replacing it. I just use the 
switch on the T-T power supply.

                 73,

                 Bob WB2VUF

On 1/2/2011 1:29 PM, Dr. Gerald N. Johnson wrote:
> 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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