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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.
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