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KX1 + KXB3080, Q7 voltages

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Kevin Simmons-2

KX1 + KXB3080, Q7 voltages

While tracking down a low power output after installing the KXB3080 into the
KX1, I was checking the voltages at Q1, Q4, Q5, Q6, and Q7 during transmit into
a dummy load. Page E-6 of the KX1 manual states there should be 0.7VDC at the
base of Q7 during transmit with a KXB30 (not KXB3080) installed. I would get
between -1.5 to -2.7 VDC at the base of Q7 with the KXB3080. I found no mention
of this change in the voltage in the supplied manuals. In fact, looking at the
KXB3080 manual, page 18, figure 15, the circuit around Q7 is not what I have
installed. The diagram shows the base of Q7 connecting to R2, a 1Kohm resistor.
I don't find this change in the procedures. The KX1 manual shows Q7 base
connecting to R28, a 1.8Kohm resistor.
I resolved the low power output issue (yay!) and the voltage at the base of Q7
during transmit is still ~-2.5VDC. The question is "What /should/ the voltage
be?" If it should now be something other than 0.7VDC, then there should be a
reference to that in the KXB3080 manual. Do others think the circuit diagram on
page 18 is inaccurate?

--
Kevin
KF0JX

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Don Wilhelm-3

RE: KX1 + KXB3080, Q7 voltages

Kevin,

There is no change in the base circuit of Q7 - that is true whether the
KXB30 or the KXB3080 is installed. You should be tracking down the source
of the negative voltage at Q7 during transmit.

Yes, the voltage at the base of Q7 should be about 0.7 volts during transmit
(long explaination of why follows:) - The source of the 6 volts during
transmit is at pin 7 of U3, then it goes through R26 and then through R28 on
its way to the base of Q7.

When the 6T signal becomes active (it should during transmit), among other
things it is applied to the base of Q7 to saturate Q7 - effectively
producing a short between the collector and emitter of Q7 - the reason is to
protect the receiver input from the transmit RF. When a transistor is
saturated the base to emitter voltage will be close to 0.7 volts - if it is
anything else, either the transistor is bad or something else strange is
wrong.

There is not a negative voltage produced intentionally in the KX1 - I would
guess you have a bad Q7 which is acting more like a diode and rectifying the
RF on its collector to produce a negative voltage at the base. If you want
to do a test to confirm my suspicion, lift one end of R28 and try a short
transmit while measuring the base voltage of Q7 - I would guess that it is
producing a negative voltage all by itself, if so, replace it (and put R28
back in place).

73,
Don W3FPR

> -----Original Message-----
>
> While tracking down a low power output after installing the
> KXB3080 into the
> KX1, I was checking the voltages at Q1, Q4, Q5, Q6, and Q7 during
> transmit into
> a dummy load. Page E-6 of the KX1 manual states there should be
> 0.7VDC at the
> base of Q7 during transmit with a KXB30 (not KXB3080) installed.
> I would get
> between -1.5 to -2.7 VDC at the base of Q7 with the KXB3080. I
> found no mention
> of this change in the voltage in the supplied manuals. In fact,
> looking at the
> KXB3080 manual, page 18, figure 15, the circuit around Q7 is not
> what I have
> installed. The diagram shows the base of Q7 connecting to R2, a
> 1Kohm resistor.
> I don't find this change in the procedures. The KX1 manual shows Q7 base
> connecting to R28, a 1.8Kohm resistor.
> I resolved the low power output issue (yay!) and the
> voltage at the base of Q7
> during transmit is still ~-2.5VDC. The question is "What /should/
> the voltage
> be?" If it should now be something other than 0.7VDC, then there
> should be a
> reference to that in the KXB3080 manual. Do others think the
> circuit diagram on
> page 18 is inaccurate?
>
> --
> Kevin
> KF0JX
>

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Kevin Simmons-2

Re: KX1 + KXB3080, Q7 voltages

Don,

Yes, you are correct. Lifting one end of R28, Q7 still had a negative
voltage at its base during transmit. I'll change out Q7.

I'd like confirmation weather the KX1 circuit diagram on page 18 of the
KBX3080 manual is correct or not. It shows Q7's base connecting to R2, a
1Kohm resistor.

Thanks Don,
73,
Kevin, KF0JX

Don Wilhelm said the following on 11/01/2006 09:55 AM:

> Kevin,
>
> There is no change in the base circuit of Q7 - that is true whether the
> KXB30 or the KXB3080 is installed. You should be tracking down the source
> of the negative voltage at Q7 during transmit.
>
> Yes, the voltage at the base of Q7 should be about 0.7 volts during transmit
> (long explaination of why follows:) - The source of the 6 volts during
> transmit is at pin 7 of U3, then it goes through R26 and then through R28 on
> its way to the base of Q7.
>
> When the 6T signal becomes active (it should during transmit), among other
> things it is applied to the base of Q7 to saturate Q7 - effectively
> producing a short between the collector and emitter of Q7 - the reason is to
> protect the receiver input from the transmit RF. When a transistor is
> saturated the base to emitter voltage will be close to 0.7 volts - if it is
> anything else, either the transistor is bad or something else strange is
> wrong.
>
> There is not a negative voltage produced intentionally in the KX1 - I would
> guess you have a bad Q7 which is acting more like a diode and rectifying the
> RF on its collector to produce a negative voltage at the base. If you want
> to do a test to confirm my suspicion, lift one end of R28 and try a short
> transmit while measuring the base voltage of Q7 - I would guess that it is
> producing a negative voltage all by itself, if so, replace it (and put R28
> back in place).
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>>
>> While tracking down a low power output after installing the
>> KXB3080 into the
>> KX1, I was checking the voltages at Q1, Q4, Q5, Q6, and Q7 during
>> transmit into
>> a dummy load. Page E-6 of the KX1 manual states there should be
>> 0.7VDC at the
>> base of Q7 during transmit with a KXB30 (not KXB3080) installed.
>> I would get
>> between -1.5 to -2.7 VDC at the base of Q7 with the KXB3080. I
>> found no mention
>> of this change in the voltage in the supplied manuals. In fact,
>> looking at the
>> KXB3080 manual, page 18, figure 15, the circuit around Q7 is not
>> what I have
>> installed. The diagram shows the base of Q7 connecting to R2, a
>> 1Kohm resistor.
>> I don't find this change in the procedures. The KX1 manual shows Q7 base
>> connecting to R28, a 1.8Kohm resistor.
>> I resolved the low power output issue (yay!) and the
>> voltage at the base of Q7
>> during transmit is still ~-2.5VDC. The question is "What /should/
>> the voltage
>> be?" If it should now be something other than 0.7VDC, then there
>> should be a
>> reference to that in the KXB3080 manual. Do others think the
>> circuit diagram on
>> page 18 is inaccurate?
>>
>> --
>> Kevin
>> KF0JX
>>
>>
>
>

Don Wilhelm-3

RE: KX1 + KXB3080, Q7 voltages

Kevin,

That is an Ooops that has not yet been caught thanks for spotting it. The
1k resistor designation in the KXB3080 manual should be R28 instead of R2,
and by the way, there is another error on that schematic excerpt too - the
value of C56 should be 68 pf instead of the 6 pf shown. It looks like the
digits were truncated in the schematic (or it was typed on an old typewriter
with a missing '8' key <G>).

73,
Don W3FPR

> -----Original Message-----
>
> Don,
>
> Yes, you are correct. Lifting one end of R28, Q7 still had a negative
> voltage at its base during transmit. I'll change out Q7.
>
> I'd like confirmation weather the KX1 circuit diagram on page 18 of the
> KBX3080 manual is correct or not. It shows Q7's base connecting to R2, a
> 1Kohm resistor.
>
> Thanks Don,
> 73,
> Kevin, KF0JX
>
>
> Don Wilhelm said the following on 11/01/2006 09:55 AM:
> > Kevin,
> >
> > There is no change in the base circuit of Q7 - that is true whether the
> > KXB30 or the KXB3080 is installed. You should be tracking down
> the source
> > of the negative voltage at Q7 during transmit.
> >
> > Yes, the voltage at the base of Q7 should be about 0.7 volts
> during transmit
> > (long explaination of why follows:) - The source of the 6 volts during
> > transmit is at pin 7 of U3, then it goes through R26 and then
> through R28 on
> > its way to the base of Q7.
> >
> > When the 6T signal becomes active (it should during transmit),
> among other
> > things it is applied to the base of Q7 to saturate Q7 - effectively
> > producing a short between the collector and emitter of Q7 - the
> reason is to
> > protect the receiver input from the transmit RF. When a transistor is
> > saturated the base to emitter voltage will be close to 0.7
> volts - if it is
> > anything else, either the transistor is bad or something else strange is
> > wrong.
> >
> > There is not a negative voltage produced intentionally in the
> KX1 - I would
> > guess you have a bad Q7 which is acting more like a diode and
> rectifying the
> > RF on its collector to produce a negative voltage at the base.
> If you want
> > to do a test to confirm my suspicion, lift one end of R28 and
> try a short
> > transmit while measuring the base voltage of Q7 - I would guess
> that it is
> > producing a negative voltage all by itself, if so, replace it
> (and put R28
> > back in place).
> >
> > 73,
> > Don W3FPR
> >

Kevin Simmons-2

Re: KX1 + KXB3080, Q7 voltages

In reply to this post by Kevin Simmons-2

Unfortunately I am still having issues with this KX1...

I changed out Q7 and there was no change in voltage reading at Q7's
base. I asked Elecraft about this and they informed me that it can be
hard to measure accurately at this spot with a DMM do to RF. It makes me
wonder if that I am seeing inaccurate readings due to RF as PO seems
fine! If I turn R4 counter-clockwise I get the correct 0.7VDC. Meanwhile
I resolved the low power issue and everything seemed fine, both transmit
and receive, but I still had the negative voltage on Q7's base with R4
fully clockwise.

Well things have gone from (seemingly) bad to worse.

I looked at other components in the path. I replaced Q6, just because I
had a hard time getting it out to test it. No change. T1's windings
didn't look quite right so I redid the green windings, re-soldered,
looks good. Checked my soldering in general, looks OK. *Now* I have low
audio and low power out on 20 meters. Everything else seems OK. I
replaced K1 because it got hit with the soldering iron during repairs. I
completely redid T2 on the KX1 board. Putting a finger on T2 raises the
noise level greatly on 20M only and there is *no* peaking of the 20M
signal with trimmer 20A. 20B peaks as normal as do all the other
trimmers for their bands. LPF1 installation looks good. So, I am now
trying to resolve a low signal/audio/power out on 20 meters.

Tnx,
Kevin, KF0JX

Kevin Simmons said the following on 11/01/2006 10:30 PM:

> Don,
>
> Yes, you are correct. Lifting one end of R28, Q7 still had a negative
> voltage at its base during transmit. I'll change out Q7.
>
> I'd like confirmation weather the KX1 circuit diagram on page 18 of the
> KBX3080 manual is correct or not. It shows Q7's base connecting to R2, a
> 1Kohm resistor.
>
> Thanks Don,
> 73,
> Kevin, KF0JX
>
>
> Don Wilhelm said the following on 11/01/2006 09:55 AM:
>> Kevin,
>>
>> There is no change in the base circuit of Q7 - that is true whether the
>> KXB30 or the KXB3080 is installed. You should be tracking down the source
>> of the negative voltage at Q7 during transmit.
>>
>> Yes, the voltage at the base of Q7 should be about 0.7 volts during
>> transmit
>> (long explaination of why follows:) - The source of the 6 volts during
>> transmit is at pin 7 of U3, then it goes through R26 and then through
>> R28 on
>> its way to the base of Q7.
>>
>> When the 6T signal becomes active (it should during transmit), among
>> other
>> things it is applied to the base of Q7 to saturate Q7 - effectively
>> producing a short between the collector and emitter of Q7 - the
>> reason is to
>> protect the receiver input from the transmit RF. When a transistor is
>> saturated the base to emitter voltage will be close to 0.7 volts - if
>> it is
>> anything else, either the transistor is bad or something else strange is
>> wrong.
>>
>> There is not a negative voltage produced intentionally in the KX1 - I
>> would
>> guess you have a bad Q7 which is acting more like a diode and
>> rectifying the
>> RF on its collector to produce a negative voltage at the base. If you
>> want
>> to do a test to confirm my suspicion, lift one end of R28 and try a short
>> transmit while measuring the base voltage of Q7 - I would guess that
>> it is
>> producing a negative voltage all by itself, if so, replace it (and
>> put R28
>> back in place).
>>
>> 73,
>> Don W3FPR
>>
>>
>>> -----Original Message-----
>>>
>>> While tracking down a low power output after installing the
>>> KXB3080 into the
>>> KX1, I was checking the voltages at Q1, Q4, Q5, Q6, and Q7 during
>>> transmit into
>>> a dummy load. Page E-6 of the KX1 manual states there should be
>>> 0.7VDC at the
>>> base of Q7 during transmit with a KXB30 (not KXB3080) installed.
>>> I would get
>>> between -1.5 to -2.7 VDC at the base of Q7 with the KXB3080. I
>>> found no mention
>>> of this change in the voltage in the supplied manuals. In fact,
>>> looking at the
>>> KXB3080 manual, page 18, figure 15, the circuit around Q7 is not
>>> what I have
>>> installed. The diagram shows the base of Q7 connecting to R2, a
>>> 1Kohm resistor.
>>> I don't find this change in the procedures. The KX1 manual shows Q7 base
>>> connecting to R28, a 1.8Kohm resistor.
>>> I resolved the low power output issue (yay!) and the
>>> voltage at the base of Q7
>>> during transmit is still ~-2.5VDC. The question is "What /should/
>>> the voltage
>>> be?" If it should now be something other than 0.7VDC, then there
>>> should be a
>>> reference to that in the KXB3080 manual. Do others think the
>>> circuit diagram on
>>> page 18 is inaccurate?
>>>
>>> --
>>> Kevin
>>> KF0JX
>>>
>>>
>>
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