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20m QCX - output power issue

 

Hi,

second solution - adding 10k resistor providing positive voltage to Q5 drain works as well, I got back to 1nF C33.

My power output was still low (below 20Vpp) so I removed all of the final BS170, checked the drive - nice, square 5Vpp, it was a bit distorted with the finals in place.

Decided to mount a few fresh 2N7000s (bought 50pcs some time ago) instead of BS170s. With just one in place, I got about same power output (~18Vpp). Mounted another one, keyed down, a flat line on the oscilloscope - and 0.8A of current consumption! Even after unkeying. 7805 got very hot, turns out 74ACT00 is now about 2,5 Ohms Vcc-Gnd and gets warm after connecting power. The second 2N7000 I mounted was apparently dead (shorted gate-source).

So, few days off until new 74ACT00 arrives and I get the necessary utilities to unsolder the old one, I hope the uC and Si5351 survived without damage. Also, 2SC(...) PNPs I bought do not work well in pulse shaping circuit - pulses begin very sharply and end too slowly (>10ms).

I think I spent more time than I should building it ;)

73 Olgierd SQ3SWF
 

Hi Olgierd,

Great to hear that the resistor solution worked for you as well.? Not so good on the FETs and driver chip though!? My board is a little battle scarred now with changing caps and Q6 several times, a couple of plate through holes came out as well.??
It is working well now though and I should not have to touch it as long as the 2N2907 holds up.? The 2N2907 may be ok now as the occasional stress of passing 1 amp is not happening any more now that it is stable.
Experimentation is all good fun!

Cheers,
Glenn VK3YY.


On 22 October 2017 at 00:48, <opilarczyk@...> wrote:
Hi,

second solution - adding 10k resistor providing positive voltage to Q5 drain works as well, I got back to 1nF C33.

My power output was still low (below 20Vpp) so I removed all of the final BS170, checked the drive - nice, square 5Vpp, it was a bit distorted with the finals in place.

Decided to mount a few fresh 2N7000s (bought 50pcs some time ago) instead of BS170s. With just one in place, I got about same power output (~18Vpp). Mounted another one, keyed down, a flat line on the oscilloscope - and 0.8A of current consumption! Even after unkeying. 7805 got very hot, turns out 74ACT00 is now about 2,5 Ohms Vcc-Gnd and gets warm after connecting power. The second 2N7000 I mounted was apparently dead (shorted gate-source).

So, few days off until new 74ACT00 arrives and I get the necessary utilities to unsolder the old one, I hope the uC and Si5351 survived without damage. Also, 2SC(...) PNPs I bought do not work well in pulse shaping circuit - pulses begin very sharply and end too slowly (>10ms).

I think I spent more time than I should building it ;)

73 Olgierd SQ3SWF


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