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looks like a snowy pic
do you have a matching transformer on the ant? 300 ohm to 75 ohm.
dark pic is often a case of weak video out tube OR just not setup right (screen drives).
You should see if there is a service switch and go thru the setup procedure.
I assume you have checked the CRT and it test ok?
Brightness is best checked by confirming as follows:
Test CRT for emissions and cut off
check HV (25kv)
check voltage at CRT pins
if the above check out the CRT pretty much has to produce a decently bright pic. the CRT pin voltages will isolate where to look.
example, if the cathode pins on the CRT are too high a voltage (results in a dark pic), then you can go right to the video out tube. A weak video out tube (or a defect in the circuit making it not draw plate current) will result in too high a plate voltage at that tube. Since the set uses directly coupled cathodes (tied directly to the plate lead of the video out) the resulting high plate voltage at the video out is coupled to the CRT. The high CRT cathodes will essentially cut off the CRT (bias it off) making it too dark.
One more thing, this is the case, but if all looks good and you have a completely dark CRT then you need to check the focus voltage. if you lose focus voltage the CRT will be completely cut off. Focus voltage should be around 4.5-5.5 kv, best tested with a HV prob.
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