Newbie's First Questions RCA TS 721 Restoration

[Chris K]

Originally Posted by Kevin Kuehn

Do you have the yoke in circuit? I don't see if you've mentioned if you have 330v on pin 10 of the CRT socket? 330v is the B Boost generated by the damper, and if it's not present or low could explain low HV. B Boost would also be measurable at pin 8(cathode) of the damper. Otherwise a weak 1B3 HV rectifier or drifted high R187 HV filament resistor could explain it.

The voltage spec sheet shows 290 for Pin 10 and I've got that. Previously I replaced the HV resistor with a new one so that's probably ok. The horizontal and vertical yoke windings ohmed out perfectly and it is in circuit. The 1B3 is old stock tested good I got from Tube Depot so I'm stumped. Maybe I'll replace it with the original and see if that makes a difference. I did order another one to try because they are so common in these sets it won't go to waste. The HV measured the same on and off the CRT. It's gotta be the tube right? The damper is new as well. I'll keep troubleshooting and see what I can come up with. I do see in the Riders schematic the B boost generated by the damper is 330V but I have a tube socket voltage chart from the Sams that references 290V.