Nice to find someone willing put put effort into **** like this. I commend it. And to use pretty high tech skills to do it, like about engineers level, modifications and KNOWING what works right and doesn't. Have any idea how hard it is to find people who CAN do that, let alone willing ? Keep it alive bro... (het, sounds like a good name for a company)

I'll put my suggestions first and commentary later to be sufferable...

The components around R 516, C 519 etc. have nothing to do with the HV level. They are for the ABL, they measure the actual HV current and cut the video gain down if it exceeds a certain level. There is not supposed to be voltage dropped there like in a CRO.

Notice the difference in the print around C 512 - 514. The 19" version has 2 extra caps there. They downed C 514 down to 2,ooo pF from 2,500. Then they added C 531 & 532. which slows down the retrace, makes all retrace rectified sources lower and trace rectified sources a little bit higher. You can tell which it is by scoping the input the the rectifier, if you see a large negative trace on a positive source it is trace rectified, if the pulse is positive on a positive source it is retrace rectified.

Question : this potted fly, CAN YOU GET TO THE CORE ? You do not have to get to the windings, if you can get to the core you can add bucking or boosting windings to any winding there. All that area that is encapsulated, can you see the ferrite thing around it ? If so, can you see a gap ? All we need is about 0.03 inches for good enough. That is big enough for # 24 AWG to get through and you can get it with like couple hundred volt insulation.

Increasing the capacitance alone might not do it, but a combination of changing the B+ and that might.

Comment :

This thing was built before internal pincusion correction in the CRTs. There is a saturable reactor and another one that is permanent magnet biased. there are also VDRs. This means that This indicated that voltage and current levels muct be at least close for good geometry. We are not talking moon shot accuracy here but we must remain within the "linear non-linearitiy" operating range of those devices.

It also seems that the B+ is lower in one than the other.; One says (somewhere) 120 regulated and the other says nothing, but both shutdown use the same resistors and Zeners, and that indicates that the B+ level is close if not the same.

If, after adding the capacitance I suggested you find that it is not enough then the next thing is to reduce the B+. but don't do it with a passive device. The best method would be to add a Zener diode of the voltage desired with the anode to ground and the cathode to to the junction of C 905 & R 914. You'll probably want to choose a standard value anyway so choose a lower one and put a pot in series. It might decrease the tightness of the regulation but bucking that we had the gain of the IC itself. Look at most of them, they try to operate in their linear range. That works to our advantage.

Keep this baby on the road !