[dominicbeesley]

Hi Col,

Glad it sounds like you're getting close to giving it some beans!

The black coating on the CRT should be earthed somehow. (This is shown as the thick line on the outside of the CRT returned to chassis on the circuit diagrm attached on P.1 of this thread).

This is the carbon like painted on stuff. Most CRTs have a little harness of wires touching this that are then earthed to chassis. This coating forms one plate of a capacitor (the other being on the inside of the CRT). The capacitor is charged up 10,000 times a second by the LOPT and stores enough energy so that one side of the screen doesn't look darker than the other.

I'm not sure of the exact connections on your set as there is that funny metrosil stick thing as well, one end of which should also be grounded. A close-up photo of where that connects to CRT top cap and the other end of the stick's connection would be informative.

This capacitor can hold a fair charge so this is why you should discharge the CRT before working on it. That was part of the job that used to scare the bejusus out of me. Now I just use a large insulated screwdriver with the shaft croc-clipped to the chassis and spark the CRT, wait a few minutes and repeat. If you want to be gentler I used to have a big meaty 100k resistor soldered to the end of a screwdriver and used to spark to that to avoid drawing too much current but I managed to drop that down the back of the bench...

I'd always use an isolating transformer with sets like these. Even if you think the chassis is on mains neutral if the switch blows again then it might blow out the neutral side and leave everything floating on live!

So I'd go isolating tranny => variac => lamp limiter first with this set as it looks like it has "previous". The lamp limiter will at least afford protection to your variac and transformer!

Can't wait to see what for the next installment!

Dom