Transponder Help

The used ones are $500 - $700 & a new one $1125. I lost my job &
would like to keep the costs as low as possible. If I bought a used
one would I be spending more money repairing it in the future? If I
spent more money for the new one is it any more reliable that a
refurbished one?

There's no way to predict, you can only play the odds that a new one will
last longer and require less maintenance than a used one. My advice - buy a
used one that passes a bench check. In the future when you have a job and
can afford it, replace with a new one if it craps out.

Or you can just go transponderless for a while, nothing wrong with that if
you can accept its limitations.

"Steve" wrote in message ...

There's no way to predict, you can only play the odds that a new one will
last longer and require less maintenance than a used one. My advice - buy a
used one that passes a bench check. In the future when you have a job and
can afford it, replace with a new one if it craps out.

Or you can just go transponderless for a while, nothing wrong with that if
you can accept its limitations.

Thanks for your reply. I would like to fly without the transponder,
but my airport is in a class B airspace, so I am grounded till I get
something running. Steve

Earlier, Scott wrote:

I haven't looked inside the new "digital" transponders, but I assume
they still have a tube in them...

I believe that that's not correct. According to the sales literature,
current-generation transponders like the last Terras, the Microair,
and the Garmin GTX series are completely solid state. No cavity tube.

Bob K.

....and thank goodness for that!

"Bob Kuykendall" wrote in message
om...
Earlier, Scott wrote:

I haven't looked inside the new "digital" transponders, but I assume
they still have a tube in them...

I believe that that's not correct. According to the sales literature,
current-generation transponders like the last Terras, the Microair,
and the Garmin GTX series are completely solid state. No cavity tube.

Bob K.

On 6 Sep 2003 17:54:31 -0700, (Bob Kuykendall)
wrote:

:Earlier, Scott wrote:
:
: I haven't looked inside the new "digital" transponders, but I assume
: they still have a tube in them...
:
:I believe that that's not correct. According to the sales literature,
:current-generation transponders like the last Terras, the Microair,
:and the Garmin GTX series are completely solid state. No cavity tube.

The Terras were solid state from first, even with the damned
pushbutton face. Also, the UPS (now GarminAT) transponder has no
cavity tube. The microair is all solid state. I don't know about the
new Narco, they are claiming all digital, but so do the newer Kings
and they do have a tube.

If you can get a used TXP with a known service history, where you know
that it has, say, 500 hours on it, it can be a real bargain. But if
you don't know how many hours it has, it's unknown. You know that at
the moment it got it's yellow tag it was working. And you know that
at some point in the future, the cavity's going to burn out and it
will cost more than the txp is worth to replace it. So, get a new
one.

I'm an instrument tech that has no avionics experience, but a heap in
laboratory equipment that has high power valves and can say that the valves
will deteriorate with time and/or use, bit like a mobile phone battery where
you have standby and operating time, but you never know how well charged the
valve is to start with.

Some valves have the filament burn out, some get leaks into the vacuum
chamber, some have bits fall of internally like a suport wire in a light
bulb can and they short things out, but most just get older and weaker.

If you can talk to the tech that did the job on each of the second hand
units, you could get a general description of how clean the unit was inside
and what sort of output power level was there to start with, but most of
these things are just general pointers and the life expectancy of a valve is
the same as the length of a bit of string!

Considering that you can get two second hand ones for the price of a new one
and still have enought left over for several cartons of beer, I'd get a
second hand one and at least the first carton to celebrate?

Peter

Whatever option you pick, don't buy a piece of avionics with a "valve"
in it. Its got a limited life for sure. Do they even make those
anymore?

You don't want to be like those old guys that you always see at Rat
Shack with a paper bag full of "valves" putting them one by one in
that crazy tube tester contraption.

Regards

) wrote in message . com...
I have a Narco AT-50 in my airplane that failed the 2-year check. I
also had it checked by a Avonics' shop. Because it was 30 years old a
repair was not recommended. The mechanic that inspects my plane said
it would be simpler to install a newer Narco that go through all the
expense of installing another brand.

That left me with the following choices: a used AT-50A, AT-150 or a
new AT-155R.
The used ones are $500 - $700 & a new one $1125. I lost my job &
would like to keep the costs as low as possible. If I bought a used
one would I be spending more money repairing it in the future? If I
spent more money for the new one is it any more reliable that a
refurbished one?

Thanks for any help! Steve

Earlier, (Jay) wrote:

Whatever option you pick, don't buy a
piece of avionics with a "valve" in it.
Its got a limited life for sure. Do
they even make those anymore?

I disagree with that advice. It excludes the vast majority of
transponders on the used avionics market, many of which can provide
excellent value.

All the old Narco AT-50, King KT-76, and Cessna transponders have
cavity tubes. Yes, the tube has a limited life. And, yes, cavity tubes
are expensive. However, for most units that lifetime is several
thousand hours.

But when your choices are between a $1100 used solid state transponder
and a $500 used KT-76, you have to think carefully about what that
extra $600 is going to buy you. Spending it only because solid state
stuff is "cool" is sort of silly. Spending it because you actually
have a requirement for the benefits of solid state design can be
smart.

I've bought two used transponders in the last five years, and both
have worked out very well. The first unit was a used but nice looking
KT-76 which I bought on the Internet for a beater airplane. We closed
the sale at an avionics shop in San Jose after a bench check looked
good. The other unit was a used Garmin GTX-320, which I also bought on
the Internet. I chose it for my glider because I specifically wanted
its low power consumption, and was willing to pay extra money for it.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24