Re: Transmit Output Power (CW) #v5

barry halterman

Rob, I have not modified the LPFs on my V4, but I did change the relays. The filter caps on the finals are rated 470uf at 25v, so no need to screw with them. On the harmonics, I did see an increase on 30 meters, but I usually don't operate that band. Other bands were with in spec.
One thing I do, (extra insurance) is run my rig through another low pass filter, external to the ubitx. 
The transmit issue at 7000khz bit me in the butt too, put me in panic mode, it did!!
I do not use a step up converter I just use another power supply that feeds the finals.
I just purchased a bunch of 2N5109 to modify my V6, my V4 has the 2N2222a in so I'm looking forward to see what improvement those will do.
Have fun!! Stay safe.. 

On Mon, Mar 30, 2020, 2:47 PM Rob French (KC4UPR) <kc4upr@...> wrote:
Thanks Barry!

I was hoping initially here to just get the output more consistent across bands.  That said, I have thought about trying to increase the output power overall as well, though I do have a couple of questions:

(1) Did you change the output LPFs at all?  Are they good with the higher power?
(2) Any issues with harmonics at the higher power levels?
(3) Did you change the electrolytics on the final stage?  (I haven't actually checked mine, but I'd heard that they were only like 16V capacitors or something.)
(4) Do you use a step-up converter, or do you actually use a separate power supply?  I was hoping to trying to keep my uBITX running off of 13.8V.

With all of the 2N2222A's, I suspect I will be able to further increase the overall output power... With the same RV1 drive level set that I had in my uBITX stock, I get about 12W now instead of 7W... but I'm not sure at what point it will start distorting.


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