HV pix tube Current

[rcafan]

How much current does a 12" picture tube need @10KV
to give proper brightness

[Eric H]

Don't know about the current spec, if there even is one but it's very little, the voltage is what's important.

If you have 10k and normal brightness then everything is fine. The HV will vary a little depending on brightness but as long as it doesn't sag below spec then it's good.

Low high voltage will reduce the brightness but it will also cause the picture to bloom or expand as the brightness is advanced.

[hi_volt]

Typical beam currents would be in the approximate range of a couple of hundred microamperes, depending on brightness.

[rcafan]

I agree, finally found a blip of data indicating that approxamate number.
I have been considering using one of the Emco HV modules to supply
HV to a restoration.

[hi_volt]

Originally Posted by rcafan

I agree, finally found a blip of data indicating that approxamate number.
I have been considering using one of the Emco HV modules to supply
HV to a restoration.

There are several manufacturers that made high voltage power supplies that would provide that voltage and current. Also check out Spellman and Rantec Power Systems (formerly PTK.....look for an old ULC-10-XX series)

[Tubejunke]

Originally Posted by Eric H

Don't know about the current spec, if there even is one but it's very little, the voltage is what's important.

If you have 10k and normal brightness then everything is fine. The HV will vary a little depending on brightness but as long as it doesn't sag below spec then it's good.

Low high voltage will reduce the brightness but it will also cause the picture to bloom or expand as the brightness is advanced.

I'm guessing he probably meant voltage, but it is common to hear voltage referred to as current for some reason. Either way, where there is voltage in a completed circuit there is current (amperes), but I have never seen a spec. of any kind in relation to HV on a cathode ray tube. We know that current (I) is found by dividing voltage (E) by resistance (R), OR by dividing watts (P) by voltage (E), just to name a couple of formulas. I'm just not sure what variables you would plug in to find "current" of CRT HV.

[hi_volt]

I used to design high voltage power supplies for high resolution CRT displays, and worked for Rantec back in the 80s. If you look up the specifications on most CRTs, they will provide a recommended maximum anode voltage and a rated beam current. For most of the monochrome tubes, the beam current will run from around 200uA to maybe 600uA at full brightness. For a color CRT, the beam current can run up into the range of 1mA to around 1.5mA. At 25kV and 1mA, there 25 watts being dissipated in the CRT, which can be quite significant. On some of the small heads-up displays we designed power supplies for, the screen was only 6" wide, and if the brightness was turned up high enough, the shadow mask would heat up and actually distort, the effect of which which you could see on the screen. Also, if you run a small CRT like that this hard and happen to lose horizontal and vertical sweep and just have a dot on the screen the energy density was enough to burn a hole right through the CRT glass in about 2-3 seconds.

[Tubejunke]

OK, sorry. Didn't know you were talking about beam current. The original post is titled HV pix tube current, which didn't lead me to think about the electron gun.