7603 CRT tick


Neil Barlow
 

Hi folks,

I have a 7603 that works quite well, but occasionally I hear a small "tick" up near the face of the CRT tube - like a quiet HV discharge.

LV and HV power supply levels are stable and spot on. And, other that the "tick", I don't see or hear any other unusual perturbations. I have noted that the body of the CRT tube was wrapped in several spots (by the factory) with a kind of metal foil - something I haven't seen so often in other 'scopes.

Any thoughts? Is this tick a "problem" or a "feature"?

Thanks in advance,
Neil


Zentronics42@...
 

Neil,
Does it also "Tick" after shutdown? If so mine does the same thing. In a quiet lab it is very noticeable. I have narrowed it down to thermal movement "expansion and contraction" of the tube and associated internal parts. I have also noticed that it does not affect operation of the unit at all. Sounds very similar to a car exhaust cooling down after shutdown.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Neil Barlow
Sent: Saturday, May 14, 2022 2:42 PM
To: TekScopes@groups.io
Subject: [TekScopes] 7603 CRT tick

Hi folks,

I have a 7603 that works quite well, but occasionally I hear a small "tick" up near the face of the CRT tube - like a quiet HV discharge.

LV and HV power supply levels are stable and spot on. And, other that the "tick", I don't see or hear any other unusual perturbations. I have noted that the body of the CRT tube was wrapped in several spots (by the factory) with a kind of metal foil - something I haven't seen so often in other 'scopes.

Any thoughts? Is this tick a "problem" or a "feature"?

Thanks in advance,
Neil


Neil Barlow
 

Zen,

I haven't yet heard this phenomenon after shutdown. Only while powered up. Otherwise, our symptoms sound rather similar.

Thanks,
Neil


Mark Vincent
 

Nick,

The high voltage lead entering the crt is likely where it is originating. That is normal. The high voltage makes static charge even on the outside of the insulation and on the face of the crt. TVs did this. Dust on the crt body will make the noise louder and can cause a leakage path to ground causing corona discharge that can be heard and will have an odour. If yours is clean, which it sounds like by the low amount of crackle, no need to clean it. I hear this on the other series that use 21kv on the pda. You do not have a problem with your scope.

Mark


Neil Barlow
 

Mark,

Thanks. Your input is appreciated.

Neil