[Elecraft] K2: Q6 very hot in TX without mod, Normal?

[Don Wilhelm]

Michael,

If you have the new 2SC5739 transistor at Q6 (plastic tab), it will run 
hotter than the previous Q6 2SC2166 (metal tab)
To tame it down, change R46 from 270 ohms to 330 ohms which will reduce 
the bias voltage during transmit.  Q6 should cool down during receive.

OTOH, if you have the 2SC2166 installed or Q6 does not cool down during 
receive, that is an indication of a problem.  Check the 8R and 8T 
voltages during both transmit and receive.  You can measure those 
voltage rails easily at the anodes of D6 and D7.  During receive D6 
anode should be about 8 volts and D7 anode should be near zero.  During 
transmit, the reverse should be true.  If there is a problem, check 
Control Board Q1 and Q2 (the controlling source for these voltages) and 
RF Board Q23 which should pull 8R to almost zero during transmit.
If Q6 stays hot during receive periods, that could indicate a shorted RF 
Board Q10.

73,
Don W3FPR

Michael van Hauten wrote:
> Hi,
> today i did  a recalibration of my K2. I recognized, that Q6 became very hot after a short time pressing TX at the mic in SSB mode, even without modulation. All voltages at the related transistors are equal to the manual. The current goes from 300mA in RX to 680mA in TX without mod. Any ideas?
> vy 73, Michael, DC0ZO
>   
>