Another KCS47 Restore...No High Voltage/B+ Down 25V

[Chris K]

Starting fresh with an unrestored chassis. I figured I'd start in the power section like everyone else does but you need to make some rigging to be able to test and adjust it.

I took a tip from Kevin and built this rig for the 5" electrostatic test CRT.



I do not have the speaker out of the cabinet and therefore, I needed to make a jumper. The 375V rail goes into the sound section and anywhere else the 375V needs to go. The jumper is on the speaker so without it, I jumped it on the speaker connector.




Where the DMM is connected reads 350V and not the 375V in the schematic. The B+ on pin 8 of the 5U4 reads around 25V lower than the approximately 387V in the service data. I did some recapping in the power section and all three electrolytic caps have been replaced with adapt-a-cap substitutes. I covered them with some cardboard tubes I had laying around but they are grounded to the chassis.

I rigged a HV cable from the metal cone energizing socket on the HV cage. I replaced the 4 film caps in this section. The flyback is a Merit direct replacement for the original one that had an open section.




I've switched out the HV rectifier, horizontal output and damper tubes numerous times with known good tubes. I get about 3KV on the anode output when I test it at the socket.

My guess is the low HV is a function of the low B+ but I'm not sure of that. I've tried several 5U4s. If this is a problem with a resistor in the voltage divider, why would the voltage be low on pin 8 of the 5U4?

Anyway, below is the section giving me difficulty. I've made no other changes in the chassis other than the capacitor replacements I listed above.