[Elecraft] KPA100 R12 Voltage query

[Les Preston]

Don

Just re-checked the voltage in-between R11, R12 and the cathode of D1 - all 
OK (same readings).

RFC5 side of R12 with Power set at 5 watts gives:-

RX           TX
144.1V    143.9V

At >11 watts:-

RX            TX
123.7V      92.1V

One thing that I did come across during the build was, the value of R4 had 
been changed to 39K, to reduce the stress on certain components, and I now 
remember that when carrying out the voltage checks on page 43 of the manual, 
my D13 cathode to ground was a little excessive at 170.8 volts.  I searched 
through the archives and found several posts which were of the same problem 
and the answer was to put the 100K resistor back in at R4 to reduce the 
voltage at D13.  Is this correct?  it certainly reduced the D13 cathode 
voltage down to 138.1V, with the rest of the checks being within spec.

73,

Les  M0BSI

----- Original Message ----- 
From: "Don Wilhelm" <w3fpr at earthlink.net>
To: "Les Preston" <les.stationmaster at dsl.pipex.com>
Sent: Monday, February 26, 2007 6:09 PM
Subject: RE: [Elecraft] KPA100 R12 Voltage query


> Les,
>
> OK, the diodes are not the problem - you have 144.6 volts on the cathode 
> of
> D1.  That voltage goes direct to the junction of R11 and R12 where you
> should measure the same thing - if not, there is a bad connection.
>
> Is there a chance that you were measuring at the wrong end of R12 and
> thought you had a problem when in fact none existed?
>
> 73,
> Don W3FPR
>
>> -----Original Message-----
>> From: Les Preston [mailto:les.stationmaster at dsl.pipex.com]
>> Sent: Monday, February 26, 2007 12:56 PM
>> To: w3fpr at arrl.net
>> Subject: Re: [Elecraft] KPA100 R12 Voltage query
>>
>>
>> Hi Don,
>>
>> The voltage checks on D1-D8 were (not good) as follows:-
>>             Anode            Cathode
>> D1        12.05               144.6
>> D2        92.80               12.03
>> D3        12.61                92.70
>> D4        39.50                12.60
>> D5        14.43                39.50
>> D6        13.49                14.48
>> D7        -25.33               -0.477
>> D8        -0.555               0.1mV
>>
>> I've replaced the diodes, but it made no difference!
>>
>> 73,
>>
>> Les M0BSI
>>
>> ----- Original Message -----
>> From: "Don Wilhelm" <w3fpr at earthlink.net>
>> To: "Les Preston" <les.stationmaster at dsl.pipex.com>;
>> <elecraft at mailman.qth.net>
>> Sent: Monday, February 26, 2007 1:08 AM
>> Subject: RE: [Elecraft] KPA100 R12 Voltage query
>>
>>
>> > Les,
>> >
>> > It may or may not be a problem.  You should turn to the DC
>> voltage chart
>> > and
>> > measure the DC voltage on each of diodes D1 thru D8.  If all of the
>> > voltages
>> > are roughly 10% low, it is not a problem, but if you have a bad
>> diode, or
>> > one of them oriented the wrong way, the variation will be much more 
>> > than
>> > 10%.
>> >
>> > 73,
>> > Don W3FPR
>>
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