13-04-2020, 02:30 PM
Mine's a 'scope story too. I was mending a rather nice Rohde & Schwarz video waveform monitor. It was a powerful beast with lots of EHT to give a bright trace of just a small section of a video waveform.
The EHT bit was working just fine, but alas as I reached across to take a low voltage measurement, the DVM probe strayed to near the EHT cap and a hefty spark leapt out to the tip of the probe. The probe did not mind much but the expensive DVM (in 1986) did!
The LCD went a deep black and could not be revived. With much sadness I put it away. I looked at it again in a couple of months and it had come back to life as the charge had leaked away. It soldiered on to give another 30 years service.
I have mended a few of those EHT generators it is part of the Marconi MkIII camera http://www.tvcameramuseum.org/marconi/mk3/bd687p1.html It's a driven oscillator and step-up transformer type, not a flyback one. Makes about 9Kv.
The Visconol's are easy to replace, more concern about the sectional wave wound transformer! The picture shows the EHT generator in the side of the picture & waveform monitor, dated to 1953. Note the anti corona ring round the octal rectifier base.
The EHT bit was working just fine, but alas as I reached across to take a low voltage measurement, the DVM probe strayed to near the EHT cap and a hefty spark leapt out to the tip of the probe. The probe did not mind much but the expensive DVM (in 1986) did!
The LCD went a deep black and could not be revived. With much sadness I put it away. I looked at it again in a couple of months and it had come back to life as the charge had leaked away. It soldiered on to give another 30 years service.
I have mended a few of those EHT generators it is part of the Marconi MkIII camera http://www.tvcameramuseum.org/marconi/mk3/bd687p1.html It's a driven oscillator and step-up transformer type, not a flyback one. Makes about 9Kv.
The Visconol's are easy to replace, more concern about the sectional wave wound transformer! The picture shows the EHT generator in the side of the picture & waveform monitor, dated to 1953. Note the anti corona ring round the octal rectifier base.
