[TenTec] Ten-Tec T-KIT 1260 6 Meter FM Transceiver final dying

[John Brier]

On Mar 8, 2013 2:52 PM, "Duane Calvin" <ac5aa1 at gmail.com> wrote:
>
> One more thought - in audio equipment, often it's the driver transistor
that
> fails catastrophically, taking the output transistor(s) with it.  You
might
> consider checking or replacing it along with the resistor you noted looked
> toasty.
>
>         73, Duane
>
> Duane Calvin, AC5AA
> Austin, Texas
> www.ac5aa.com
>
>

But I can hear myself from it within a half block on another radio. If
the driver were fried, would I still be able to do that?

>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Stuart
> Rohre
> Sent: Friday, March 08, 2013 1:46 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Ten-Tec T-KIT 1260 6 Meter FM Transceiver final
dying
>
> John,
> First of all something besides the final was bad which caused the new
> final to fail.  The resistor is a good suspect.  Do you have a scope?
>
> That would be a help in finding out if you need the "fix" for excessive
> low frequency gain, ie any off 6m signals.
>
> What was the purspose of the suggested series capacitor on the antenna
> connector, (I am thinking you said series).  AC (and RF) coupling by the
> cap should not hurt.  It does put a reactance in series with the
> antenna, but maybe they were worried about the final collector shorting
> to an external ground if an antenna cable failed?
>
> I would talk to Ten Tec again and determine the "why" of each mod.
> Obviously, some of these rigs worked without them.  That need for a mod
> can come about because the gain of transistors may vary from unit to
> unit due to production variations.  They may not find that out in
> prototype testing, but only after customer experiences are totaled.
>
> If you wanted a "beefier"
>   transistor than the NTE replacement, you need to find the same
> polarity of transistor, NPN for example, equal or greater collector
> power rating, about the same Beta and F tau, to insure duplicating the
> operation parameters of the original.  The voltage ratings need to be
> about the same, although higher Vce voltage rating can be useful if it
> does not increase the capacitance greatly.  Not being able to look at a
> schematic right now, these are general comments aimed at any replacement
> of an out of production transistor.  You could also check with RF Parts
> Co. who handle some power transistors that are less common now.
>
> One of the issues with power transistor troubleshooting, is that you
> must have sufficient accuracy in measurements to recognize an abnormally
> low resistance.  A good visual inspection of all components for signs of
> heating should be the first thing to do; with high intensity light and a
> magnifier, upon starting troubleshooting before even powering on a
> circuit. After replacing components, do resistance checks to see it you
> have reasonable values, just to catch the rare solder bridge, or bad
> joint that can happen in replacement soldering.
>
> Good Luck to you; there should be many hours more fun with the 1260,
> once you get the final sorted out.
>
> Stuart Rohre
> K5KVH
>
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