What is the function of AKB on XG? How does it work?

Think of it as dynamic white ballance setting. AKB=Auto Kenny Bias.

How does it work though on a tech level?

I'd like to understand exactly how it works from a user perspective. How does it interact with the white-balance settings in the pots and the software white-balance (bright gain, bright bias, etc)? What exactly is it doing when you turn it on -- looking for a target G2 voltage and adjusting to that? Why do you have to save with AKB on and then save with AKB off?


BTW "K" is old (like 80-100 yrs ago) shorthand for the cathode / cathode voltage in a vacuum tube. So AKB is the Auto K (cathode voltage) Bias setting. I think. Or maybe it really IS biased about Kenny....

I thought I'd BUMP this thread, because I'd like to know more about how NEC's AKB works too. What settings does it change? I click it on, it fixes my color balance, I turn it off and it stays fixed (at least for awhile). What exactly is going on with AKB?


shoot

I'm interested as well. I've always known what AKB is *FOR*, but never really understood how displaying 3 lines above the screen does what it does...


Kal

Each neck card measures the beam current of each tube while it's line is present. The line is a known value of drive. I'll guess it's 5 or 10%. The projector then sets the cut-off so the line is indeed it's 5 or 10% of max beam current. If the measurement is 3% of the expected current then the projector will increase the cut-off until the expected reading is attained. Opposite if the measurement is 15%. The cut-off can be changed with the G-2 or the G-1 or cathode voltage can be changed.


I hope I'm saying that clearly.


Scott

Yes, Scott, thanks for that very clear explanation. Makes sense now. I'm still not quite sure what the XG is doing when you turn on AKB, store it, turn off AKB, store it .... You would think that storing it when AKB is on would be enough, but apparently not!

Well, when you turn it on it activates(duh) and then you store the value it generates. But it also stores the fact that it's on.


So you have to turn if off again, and store, to store the fact that it's turned off. Nothing actually to do with the AKB function.


I love the way you can turn it off completely on a NEC, and activate it just by hitting Brightness. Brilliant.

Scott - THANKS - I couldn't figure out how it worked, since I knew dang well that my pj didn't have an ACON type camera - I reckoned that the AKB line couldn't do any good unless there was some kind of sensor reading it off the screen. Way cool - that the pj grabs it inside the projector.


btw, I have a PG, but I guess it works the same; Mark - can't I just turn on AKB for a while, and then turn it off, or do I have to actually do something to store whatever value it sets for itself? ta.

In my experience (say you have a raster lighting up really bad from twiddled pots), when you turn AKB on in the INFO screen, or hit BRIGHT/KELVIN - it will fix the raster issue (G2 too high) straight away.


But if you don't save, the issue will be there again if you shutdown/startup. I have no idea how it works (AD convertor?), but it seems you actually have to hit STORE for it to stick.


I don't know what happens if you enable/disable then store. I've always stored with it turned on.


It seems to work instantly though - all the instructions to wait 10 mins just seem to be taking the cautious approach.

I'll vouch for the "works instantly" approach. I was shocked as h*ll when, after fixing my G2 pot issue and went to adjust a different source the rasters were whacked again until...I hit kelvin and all was well (instantly).


-Mike

Thanks Scott. I think there should be a current source for reference. If it drifts or is misadjusted, how do I check it and adjust back in my XG. Or just to let this function off is a good choice.


SYC

I hardly turn it on while using the PJ unless I am doing something in the menu.

I hit brightness every say 20 hours or so and then save it to compensate for any electronics/tube shift over time.

I wonder if something is wrong with my XG's AKB, or if I have hosed something in my attempt to recalibrate per the SM? My gamma is way high (dark crush, no shadow detail if I set it for "fade to full black"), but if I boost the brightness to see the darks, I see raster artifacts. I also notice changes in brightness when I hit the BRIGHTNESS control, so apparently the AKB is kicking in and changing something. But then I can save it and it does the same thing next time I power up. ??

We have been over this before. If there is too much discrepancies between full shadow detail and brightness level sounds like classic G2/white ballance mess to me. In my case there is only one click like going from 60 to 59 in brightness setting. Sometimes too much gain amplitude causes shadow detail crush as well but that needs scope to set.

If AKB is on and you turn the PJ on when cold, you will see a slight boost (one or two clicks of brightness) in brightness level but will go away slowly as it warms up to calibrated level in about 10~30 minutes). So temp has an effect. when you guys trying to set the G2/white balance with hood down it is probably the difference. Last time i did my g2 I set my brightness at 58 intentionally then when I put the cover back on I had to set the brightness to 60 later. It is an analog system. Any way for this reason I turn my AKB off so when it is cold I don't get that brightness boost. I hope it helps.


Edited for missing word "two" in first paragraph.