(30-04-2013, 06:05 PM)Miguel López Wrote: I did it with a high frequency oscillator at 20kHz, but I had a noise in the trace. See post#34
Have a close look at the earthing arrangements. You might have a return EHT current passing through a conductor (which could be the chassis itself) and modulating the scanning voltages or getting into the 'front end' of the vertical amplifier.
It looks like you have a mu-metal screen for the tube. Is it earthed? If it is, make sure it is earthed at one point only and choose that point carefully.
I've also looked at the under-chassis wiring. The EHT circuit, X and Y circuits could probably benefit from some screening: I see a lot of unwanted capacitive and inductive couplings there, on account of the layout. It would probably be beneficial to put the EHT transformer into a metal box too.
Al.
