Mike,
Of some concern is the heating of Q6 - but I don't think it is
unreasonable if you can still hold your finger on it.
Hint for troubleshooting. *IF* the problem is in the RF amplification
chain (Q5 thru Q8) then it should appear in TUNE as well as in SSB.
I would suggest that you measure the DC voltages for Q5 thru Q8 after
the K2 has been idle for some time, and then after some period of
operation after which the distortion could be expected to begin.
One thing you might want to try is to measure the resistance from the Q6
emitter to ground before distortion begins and after it starts. It
should be 1.5 ohms (so use a low resistance scale). If it changes,
consider replacing R50, but also be aware that there may be something
causing the voltage on the base of Q6 to change as well.
If your Q6 is a 2sc5739 instead of a 2SC2166 (the 2SC5739 has a plastic
tab instead of the metal tab on the 2SC2166), then change RF Board R46
to 330 ohms.
73,
Don W3FPR
On 2/3/2019 1:26 AM, mustang65 wrote:
Don,
I have done some measuring on the powerstage.
dc voltage during tuning is 14,1 v
Bias Q7 is 0,652v when tuning.
U1 pin6 43mV on ssb transmitting.
I get about 10w max output (do not have a bird)
all measuring was done with a fluke 179.
Q6 gets mutch varmer then Q7,Q8 is this normal?
The strange thing that is confusing me is when the k2 has been turned of
over the night
there is almost no distorsion when I start to transmitt .
then it slowly arrives in the first couple of minutes.
73 Mike sm3xgm
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