hv is all over with scene changes, clearly hv cant keep up with demand for whatever reason so far.

I am not sure what you mean by "can't keep up" but if you mean the HV is not regulated then then the reason is:

1) HV shunt is not operating correctly (a missing jumper would for sure do this as an example)

2) there is not enough HV in reserve (so the shunt has nothing left to shunt, and the HV drops) this can be a weak tube or other problem in the HV system.

3) CRT load too high from incorrect setup or defect in circuit or bad CRT.


Answer the following please (in order)

What is the HV (in kV) with the shunt tube cap off and the brightness all the way down? Make sure the tube cap is not near anything as it will arc.

replace the shunt tube What is the HV now(in kV)?
brightness up
brightness down

with brightness down does the HV adjustment pot have any effect on the kV?


Its important to answer the all the above questions prefer in that order asked to try and figure out whats going on. It would help if you would quote this and answer each question.

i have done this in the beginning and the fly was said to be ok so the reg tube cap off was around 30kv alot of hiss. cap back on 24kv with the hv adjust at max if i turn it down it will lower the hv. bright up or down the hv adjust does work but to get just the 24kv it has to be maxed.

well the jumper was closed so i broke it put a meter in and im getting 5ma and hissing in the cage and sometimes an arc at the crt neck with the brightness not all the way down, the ma goes up if the bright is all the way down. ok im lost . i forgot to mention with bright up i get 1.2ma- 5.3ma it jumps from both readings.

That does not sound right. the shunt should be around .5ma on full raster, too about 1.5ma full dark. I suspect your are not reading something right or your meter is not working correctly if you are seeing 5ma

you need to put the HV meter on the CRT, put the current meter in the jumper and watch the HV vs Shunt tube current as you adj the brightness on a raster.

Set the HV pot for 24kv then adj the bright up and down note the shunt current, if it goes up as the crt goes dark and goes down as the crt brightness increases, then the shunt is working as it should.

If the above is correct (shunt working as it should) then you need to go back and recheck the HV setup, starting with the cathode current dip on the eff coil.

when you get all that sorted out and have the correct meter readings (.5-1.5ma shunt). Then you can restart the trouble shooting. One other thing, assuming the HV is ok is the focus voltage can cause what looks like blooming including complete darkness on the CRT. The pin and or the socket at the CRT sometimes fails from corrosion.

oh I would recommend an analog meter if you are not using one. Something like a simpson 260. I don't like to read current readings that move quickly with DMM.

also try a new HV rectifier tube.

well i did use a fluke digital meter and i do trust it but lowering the brightness is causing arcing and the ma does raise up the lower i put the brightness. so ok ill follow the above again. and i did have the meter in the ma setting. all i can do is leave the hv adjustment where it is now which is at max 24kv is all i can get. as far as the blooming with the hv probe in place if i just move the crt bias a touch it blooms and the hv drops dramatically.

where exactly is the arcing? you really want to avoid that.

I cant see enough of the schematic, but need to know where R135 goes.

some sets tie in the video signal from the video out tube into grid of the shunt. This is done for more rapid adjustment of HV.

Make sure C99 is not bad if you have HV reguation problems.

ok here goes i have an analog meter and hv probe in bright down 24kv and not even half ma on the meter bright up around 23kv and even less then half ma. the arc was happening at the crt neck just a couple of times.

looks like r135 1.5 meg goes from grid of reg tube to hv adjust pot and horiz lin. c99 cap was changed its a .00
33 ceramic. the meter i used i know now that it has 5ma increments so the amount it moved i think its safe to say that i got .5 and 1.5 ma because it never got near the 5ma line.

ok now we are getting somewhere. try a new HV rectifier tube 1st. then check the sams see if it mentions adj the horz eff coil 1/4 turn to bring that shunt tube up to spec (.5-1.5 bright to dark). You may not be right at the lowest point but I think a minor tweek is allowed (no more than 1/4 turn).

When I setup a set the normal deal is to have a meter on the horz out tube cathode, a meter on the shunt tube, and the HV meter on the CRT anode.

adj the eff coil for lowest setting, set HV to 23-24kv, check shunt current, as long as there is some current flowing in the shunt with a full bright raster, then you should be ok (and the HV should hold steady at 23-24lv) If you have no current flowing in the shunt then you can reduce the HV to 22kv see if that does it. then try 20kv if still nothing then you can tweek the eff coil. It drives the fly a bit harder so you dont want to go overboard.

all of the above assumes there are no other issues. I would think a weak tube in the HV section would be the 1st place to check.



again your are trying for some flow of current in the shunt with a full bright raster, that shows you have some reserve HV and the regulation via the shunt should hold the HV steady.


I would also try another horz output tube/damper/hv rectifier. If the emissions are low on any of these HV performance will suffer.

i have tried several rec tubes, reg tubes , horiz tubes, and damper tubes nothing ever changed and i had checked the cathode current and with scene changes the cathode current would jump over 220ma so i had lowered it to a steady 200ma but i had raised it and lowered it with nothing ever changing for the better.

ok so you are seeing .5ma to 1.5ma depending on raster brightness? of so then shunt is working.

HV holds steady thru those changes (raster brightness)? if the shunt is working then this should be steady.


if the above is correct then maybe there is something wrong with the video output that is causing a bias issue at the CRT, the video output during normal siganals (not raster). Is this what is happening?