[TenTec] Re: 1340 side tone

[Steve Ellington]

Bill:
Turn to page 23, Phase 4.0 Schematic Details. Find Q20 in the lower left
part of the page. Note that it's collector connects to the lower end of the
sidetone level pot. Its not obvious but it's true! When you key down, D13 is
forward biased making it conduct which in turn forward biases Q20 which in
effect, grounds the collector thus grounding the lower end of R61 (sidetone
pot). This action causes the voltage to decrease on the center arm of R61,
lowers the bias on Q8 thus greatly decreasing the signal comming off the
collector of Q8. The signal going into the 11MHZ bfo/mixer is thus reduced
to provide a comfortable sidetone level.

In addition to all of this, Note that the collector of Q8 goes to the AGC
circuit, namely C43. This means that the signal from Q8, I.F. amp, will
develope across D5. If a strong signal is present, D5 will conduct and shunt
the IF signal to ground in porportion to the signal strength. So we have two
things working to prevent that huge noise you keep hearing.

First, I would check D13 to see if it's not in backwards. If not, measure
the voltage on the center arm of the sidetone pot. It should be about 12
volts. Then key the rig and see if this voltage drops. With the sidetone
adjusted to minimum, arm toward Q20's collector, you should be able to make
the voltage almost zero. If not, then trace back through Q20, R62 and D13 to
find the problem. If all is ok, check Q8.

If you don't think the agc is working, check the direction of diodes D3, D4
and D5. The voltage on the base of Q7 will flucuate with signal strength.
This would be a good place to tie in an S-meter circuit!  Measuring the
voltage on D5 doesn't work too well because your meter will shunt RF to
ground and fool the circuit.

Let us know how it works out. 73

Steve N4LQ



>Steve,
>Thanks for your suggestion, which is probably true, but leaves me in the
>dark for where to search for a wiring error.  Mike, N4NT, billed you as the
>1340 expert.  So if you don't mind I'll quiz you more.
>
>Here are the symptoms, and what I've done.
>
>THE SYMPTOMS
>1. The side tone is ear splitting loud
>
>2. The tone appears with a very loud click on key down.  I might add that
>this click has not been in evidence in reports on the air (I have had 4
>QSO's with the rig, 2 domestic and 2 dx.  All gave it excellent
>characteristics)
>
>WHAT I HAVE DONE
>1. Examined the thing visually for solder bridges, etc.  My untrained eye
>found nothing.
>
>2. Posted a question to the reflector.
>
>3. Called TenTec.  Gary Green there had just two suggestions.  He thought
>that I might have put the incorrect number of turns on the toroids L8, L9
>and L10.  I checked these and they are correct.  He also suggested that I
>reposition the toroids, push them around a bit with respect to each other.
>I did that as well, with no effect.
>
>4. Read the suggestion from Mike that pot R61 might have a leg that should
>be grounded, why didn't I check the schematic to see if that's so?  Well,
>the only poor part I have found about the T-kit is the schematic.  The
>section containg R61 is unreadable.
>
>I'll call TenTec again tomorrow, but in the meanwhile, do you have any
>suggestions on how I could trouble shoot the thing?
>
>73 Bill NY3M
>
>


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