[Penthode]

Been cleaning the considerable gunge off the chassis this week. Removed the high voltage compartment and the selenium rectifier frame to give it a thorough clean. Started replacing paper capacitors in the HV cage and now that it is clean have given it a thorough inspection.

Whilst making checks around the selenium rectifier, found a fuse blown and a jumper wire which had been placed across it. Not good. Then the resistive ballast if that is what it is called I examined and found part of it open. Closer examination revealed it appears to be simply a voltage dropped with an 800 ohm and a 300 ohm resistances to each drop the 400v DC supply to 285v. 115v across the 300 ohms dissipates 41 watts and 800 ohms 16 watts. The 300 ohm section is the one open.

It looks to me a bit of a bad design wasting 56 watts like this. That is a good chunk of the total 475 watts the setg consumes. I guess power was cheap in those days!

Anyhow think what can I do to salvage this? I found a 50 watt 330 ohm and 25 watt 820 wire wound chassis mount resistors back to back will just fit the 30cm diameter ballast container. But that is a lot of power to dissipate.

Has anyone else dealt with this or have any ideas?