Help with KPA 100 Alignment and Installation

[Les and Lynn]

Folks,

I solved the problem with the SWR Bridge null adjustment (CI) by reflowing a bunch of solder joints (i.e., Don's usual suggestion) around T1, R21 and R22.

However, now I have a new problem -  I am drawing to much power in the transmit tests of on pg 50 of the KPA 100 manual. My metered Astron switching power supply shows 25 Amps on key down (2-3 sec.) at 100 watts. Calculating the amperage across R7 shows 21 Amps - still to much. Q1 seems to get preferencially hot compared to Q2 during the 2-3 sec.key down. The signal sounds great in a remote receiver. Changing the values of R26 and R27 doesn't seem to effect the power reading.

I probed voltages and the deviating voltages are shown below:

Q1 RX - All OK
Q! TX - B=0.532V and C= 13.26 V  Note - Voltage input at  K2 Display is 14.2 VDC

Q2 RX - All OK
Q2 TX - B=0.523 V and C= 13.28 V

Q3 RX - All OK
Q3 TX - B= 0.543 V

Q4 RX - All OK
Q4 TX - C=14.23 V

Q5 RX - All OK
Q5 TX - B = 2.8 V and C=0 V

Any ideas on what to do next would be appreciated.

73,

Les WA3SGZ

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[Don Wilhelm-3]

Les,

The most usual reason for excessive current is the Low pass filters -
check the toroids for an extra turn - count the number of times the wire
passes through the center of the core.

Also carefully check the calibration of the wattmeter forward power pot.

Also check the bias setting again, and re-check the number of turns on
the T1 and T2 transformers.

73,
Don W3FPR

Les and Lynn wrote:

> Folks,
>
> I solved the problem with the SWR Bridge null adjustment (CI) by reflowing a bunch of solder joints (i.e., Don's usual suggestion) around T1, R21 and R22.
>
> However, now I have a new problem -  I am drawing to much power in the transmit tests of on pg 50 of the KPA 100 manual. My metered Astron switching power supply shows 25 Amps on key down (2-3 sec.) at 100 watts. Calculating the amperage across R7 shows 21 Amps - still to much. Q1 seems to get preferencially hot compared to Q2 during the 2-3 sec.key down. The signal sounds great in a remote receiver. Changing the values of R26 and R27 doesn't seem to effect the power reading.
>
> I probed voltages and the deviating voltages are shown below:
>
> Q1 RX - All OK
> Q! TX - B=0.532V and C= 13.26 V  Note - Voltage input at  K2 Display is 14.2 VDC
>
> Q2 RX - All OK
> Q2 TX - B=0.523 V and C= 13.28 V
>
> Q3 RX - All OK
> Q3 TX - B= 0.543 V
>
> Q4 RX - All OK
> Q4 TX - C=14.23 V
>
> Q5 RX - All OK
> Q5 TX - B = 2.8 V and C=0 V
>
> Any ideas on what to do next would be appreciated.
>
> 73,
>
> Les WA3SGZ
>

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[Don Wilhelm-3]

Les,

Check to be certain you have installed Q6 and Q7 the correct way 'round.

Second, what is the value of C31 in your kit?  It was recently changed
to 0.22 uf to cure an oscillation that occurred in a few amplifiers with
the new T-R switch design (Rev D manual).

The kits available in February may or may not have had the .22 uf C31
packed.  If you have a .033 uf cap at C31, request a .22 uf cap for C31
from [hidden email]

73,
Don W3FPR

Les and Lynn wrote:
> Folks,
>
> I solved the problem with the SWR Bridge null adjustment (CI) by reflowing a bunch of solder joints (i.e., Don's usual suggestion) around T1, R21 and R22.
>
> However, now I have a new problem -  I am drawing to much power in the transmit tests of on pg 50 of the KPA 100 manual. My metered Astron switching power supply shows 25 Amps on key down (2-3 sec.) at 100 watts. Calculating the amperage across R7 shows 21 Amps - still to much. Q1 seems to get preferencially hot compared to Q2 during the 2-3 sec.key down. The signal sounds great in a remote receiver. Changing the values of R26 and R27 doesn't seem to effect the power reading.
>
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