Posted by
Bob Towers on
Dec 13, 2007; 6:00pm
URL: http://elecraft.85.s1.nabble.com/KPA-100-QRP-except-on-80m-tp456874p456878.html
Many thanks, Don, for your comments.
Here's my replies...
Don Wilhelm wrote:
> "Bob,
>
> What have you finished of the Testing and Alignment. If you have not
> yet done the PA bias adjustment, your KPA100 will have little or no
> output as you describe. "
I've done SWR calibration, power calibration, power supply test, fan
test, external keying test, PA bias adjustment and power tests <= 11
watts. I've started the 20W power tests and that's where the problems
appeared.
>
> "Actually I had some trouble understanding your exact problem.
> Do you mean that you have no KPA100 output on 80 meters, but it is OK
> on other bands? Or do you have no hi power output on any band? Or,
> do you mean that you have about 11 watts of power anytime the power
> request is set above 11 watts? "
I have hi-power on 80m only. All the other bands (I don't have 160m)
only power up to 11W. Over 11W, K1 latches, but the power then drops to
around 1-2 watts. There is no increased bias to the PA finals.
>
> "It is not 'T sense' - that only controls when the fan comes on."
Thanks! I thought it was the control to switch the bias to the PA.
>
> "If QRP transmit is OK, then likely your Low Pass Filters are good -
> check on all bands. "
Yes, QRP transmit on all bands is OK.
> "If you receive properly when set to 11 watts or higher, then at least
> part of the T/R switch is working properly."
I'll check that one.
>
> "Calibrate your wattmeter initially at 9 or 10 watts (you can re-do it
> at higher power later), but the wattmeter must work to control the
> power of the K2 (and the KPA100). "
Yes, I've already done that via R26.
>
> "If your problem is that you have some power output when the power
> request is set above 11 watts, but not the proper amount, then check
> the Scaling function of the wattmeter - RP1, R24 and R25 and Q10 and
> Q11. During hi power transmit, the drain of Q10 and Q11 should be
> near 0 volts and you should have 4 to 6 volts on the gates. "
I'll check that one, too.
A feature so far is that I only get the correct bias voltage (base of Q4
= 1.51V @20W O/P) on 80m. On all other bands, it stays unchanged at
0.52V when I move from <11W to >=11W (the point where K1 latches).
>
> "73,
> Don W3FPR "
73
Bob MM0RKT
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