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

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Ten-Tec T-KIT 1260 6 Meter FM Transceiver final dying
From: Stuart Rohre <rohre@arlut.utexas.edu>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Fri, 08 Mar 2013 13:46:09 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
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

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