Topics

Ubitx - Increased voltage to finals thru middle wire on power plug...no effect

Kevin Rea
 

hi guys,
I thought i would try a little experiment.
I was running 12 volts on the dot to the middle wire on the power plug on my v4 ubitx
and the output is about 16 watts on 20 meters cw.
I then increased it to 23 volts, and the output was the same, about 16 watts on 20 meters cw.

I thought there was going to be some increase ?

Here are a couple shots..
kevin rea
lancaster, calif.
k6rea




John (vk2eta)
 

Hi Kevin,

The finals (IRF510s in particular) are sensitive to supply voltage. Even when going from 12 to 13.8V the increase is visible.

The first thing that comes to mind is current limitation although it would be quite a coincidence that it results in the same power output.

Easy first test is key the rig in ssb, no modulation, and check the voltage on the cooling tab/heat sinks of the finals to verify that you get the higher voltage on the drains of the finals.

73, John

ajparent1/KB1GMX
 

Kevin,

Increasing the voltage to the finals only helps if there is RF drive enough to 
take advantage of it.

Its true for the IRF510, RD16HHF, MRF150.  They all have so much gain
and more voltage does not significantly increase that.

Likely if you were not limited by the TD2822 and you increase the 12V to
say 14V you would see a corresponding increase output power.

Most all of the uBitx I've encountered had a mod to keep teh voltage to the tda2822
and tuning up the voltage from 12 to to 13.8 made a noticeable difference on any band.

Like John said also make sure you actually are delivering increased voltage.
Your power supply could be fading under the current draw.

Allison

John (vk2eta)
 

Correction Kevin, no need to key the rig. I forgot that the finals are always connected to the power supply.

73, John

Adrian Waiblinger
 

Wow something not right there.  You got current limit on ? It’s very voltage sensitive.

  I’m getting on 20m 13.8v 14watts cw (2.2amps).  At 17volts 20watts at 2.7amps.  



image1.jpeg
Lovely 3rd can be seen.  Doesn’t change with pa voltage.

Regards 
Adrian 


On 17 Aug 2018, at 12:06 pm, John <vk2eta@...> wrote:

Correction Kevin, no need to key the rig. I forgot that the finals are always connected to the power supply.

73, John

Kevin Rea
 

hi Adrian, no I do not have any current limiting that I know of I'm powering the 12 volts with 5 amp and then I'm powering the sitter lead of the power connector with a 5 amp at 23 volts and I am getting 23 volts at the finals. Still ,no difference in output.

Kevin Rea
 

Hi Adrian,
is there a current limit somewhere in the rig?

Kevin Rea